WEBVTT 00:01.167 --> 00:02.497 G. BARNEY ELLISON: I'd like to see if I can 00:02.500 --> 00:05.400 describe to you how you could 00:05.400 --> 00:08.870 measure the bond energies of complex molecules. 00:08.867 --> 00:12.827 And to start out, let me just remind you what 00:12.833 --> 00:13.773 we're talking about. 00:13.767 --> 00:15.397 Let me talk about something like methane. 00:15.400 --> 00:17.370 I'm going to need a larger stick. 00:17.367 --> 00:22.067 So if you have methane, and you want to measure the bond 00:22.067 --> 00:26.497 energy, I literally want to reach in and measure the 00:26.500 --> 00:29.870 energy it would take to grab that hydrogen and literally 00:29.867 --> 00:31.227 just rip it out of there. 00:31.233 --> 00:33.603 And when you can see it does that, the molecule is going to 00:33.600 --> 00:35.330 have a change from a tetrahedral 00:35.333 --> 00:38.073 geometry to a flat geometry. 00:38.067 --> 00:40.867 And there's a potential curve that I've written as a Morse 00:40.867 --> 00:41.827 oscillator. 00:41.833 --> 00:44.303 And there's a zero point energy, and you're going to 00:44.300 --> 00:47.730 have to measure the energy to go from the ground states up 00:47.733 --> 00:52.173 to the dissociation limit. 00:52.167 --> 00:57.927 So I thought I'd try to tell you, just in a simple way. 00:57.933 --> 01:01.103 If you took a molecule, and you'd like to try to see if 01:01.100 --> 01:04.270 you could measure the different bonds in the molecule, 01:04.267 --> 01:08.827 how could the specific bond energies be measured? 01:08.833 --> 01:12.073 And let me consider something like methanol. 01:12.067 --> 01:14.567 I'd like to take methanol, and I'd like to show you how you 01:14.567 --> 01:19.167 measure the bond energy to break the OH bond, then how 01:19.167 --> 01:24.267 you'd break the CH bond or how you'd break the CO bond. 01:24.267 --> 01:25.697 And I don't want to calculate this. 01:25.700 --> 01:28.230 I actually want to measure it. 01:28.233 --> 01:36.873 So one way you can do this is to use a gas-phase-acidity- 01:36.867 --> 01:39.627 electronegativity cycle. 01:39.633 --> 01:46.233 This is a negative-ion cycle that you'll take this 01:46.233 --> 01:50.073 molecule, say, methanol, and if you treat this with a base 01:50.067 --> 01:53.627 such as its fluoride ion, the fluoride ion is actually going 01:53.633 --> 01:54.473 to attack the methanol. 01:54.467 --> 01:58.527 And when it does this, it's going to pull a proton off. 01:58.533 --> 02:00.703 And if it does that, you'll form a methoxide ion. 02:05.500 --> 02:10.070 The fluoride ion will never pull the proton off the 02:10.067 --> 02:12.967 carbon, because the negative ion that you get has the 02:12.967 --> 02:15.867 electron sitting on the carbon, and the oxygen is more 02:15.867 --> 02:20.127 electronegative, so you'll always get the top ion. 02:20.133 --> 02:26.333 So if you could do that, what you'd like to think about is, 02:26.333 --> 02:29.003 how can I measure an equilibrium 02:29.000 --> 02:31.230 between these two species? 02:31.233 --> 02:34.833 And if I have the equilibrium, I can get the enthalpy, and if 02:34.833 --> 02:39.133 I can get the enthalpy, I can get the acidity of this. 02:39.133 --> 02:45.903 So this is an experiment that a bunch of us do in Boulder. 02:45.900 --> 02:49.630 The world's expert in these gas phase acidity measurements 02:49.633 --> 02:55.403 is my colleague Ronnie Bierbaum, PROFESSOR MCBRIDE Doctor 02:55.400 --> 02:57.830 Veronica Marie Bierbaum. 02:57.833 --> 03:01.473 And she's very good at this. 03:01.467 --> 03:06.427 They have a flow tube, and this is the experiment you 03:06.433 --> 03:07.333 want to do. 03:07.333 --> 03:12.303 So you would like to measure the reaction of fluoride ion 03:12.300 --> 03:16.030 pulling a proton off methanol to get the methoxide ion. 03:16.033 --> 03:20.473 So what you do is...here you can't get a lecture bottle of 03:20.467 --> 03:23.897 fluoride ion, because they're charged. 03:23.900 --> 03:26.800 So what you've got to do is take a gas, 03:26.800 --> 03:29.230 and you make a plasma. 03:29.233 --> 03:31.203 You boil electrons off a filament. 03:31.200 --> 03:34.700 And as the electrons interact with the HF, the electrons 03:34.700 --> 03:37.600 get captured into a sigma* orbital, and the molecule 03:37.600 --> 03:41.730 detonates and gives you an F minus and hydrogen atoms. 03:41.733 --> 03:48.473 So the fluoride ions are injected into this flow tube. 03:48.467 --> 03:49.667 And there's methanol in here. 03:49.667 --> 03:53.967 And what happens is, as the reaction proceeds, the 03:53.967 --> 03:56.727 methanol has a proton removed from it. 03:56.733 --> 04:00.273 And you're literally watching the end of the flow tube with 04:00.267 --> 04:01.867 a quadrupole mass spec. 04:01.867 --> 04:04.667 The quadrupole mass spec monitors the negative ions 04:04.667 --> 04:08.397 that have m/Z 31, and you'll watch them growing in. 04:08.400 --> 04:12.400 So as you watch the methoxide ion going in, you can measure 04:12.400 --> 04:15.730 the rate constant K1, that goes this way. 04:15.733 --> 04:19.473 So if you do that, what you're after is 04:19.467 --> 04:20.927 the equilibrium constant. 04:20.933 --> 04:24.933 So to get the equilibrium constant, one way to do this 04:24.933 --> 04:28.673 is that you would measure the reverse rate. 04:28.667 --> 04:34.967 So if you did that, to measure such a reaction, now you'd 04:34.967 --> 04:38.227 just turn the reaction...you do the reverse of this. 04:38.233 --> 04:43.573 You now have to make a vapor of methoxide anions. 04:43.567 --> 04:46.467 An easy way to do this is to have electrons interact with 04:46.467 --> 04:47.797 methyl nitrite. 04:47.800 --> 04:50.830 The methyl nitrite then disintegrates, and it forms 04:50.833 --> 04:53.833 methoxide anion and nitric oxide, NO 04:53.833 --> 04:56.633 And the methoxide ion then goes down the flow tube. 04:56.633 --> 05:00.303 And if the methoxide ion interacts with the HF, now 05:00.300 --> 05:02.870 what you'll see is F minus growing in. 05:02.867 --> 05:05.327 And you know it's F minus, because Jesus only made a 05:05.333 --> 05:07.903 finite number of ions that have m/Z 19, 05:07.900 --> 05:08.830 and fluoride is it. 05:08.833 --> 05:10.133 There's no other. 05:10.133 --> 05:12.233 So it turns out when you do that, you're 05:12.233 --> 05:14.533 able to monitor this. 05:14.533 --> 05:20.603 So if you've measured K1 and you've measured K minus 1, 05:20.600 --> 05:23.770 that is going to give you the equilibrium constant. 05:23.767 --> 05:26.867 And this is the difference in acidity between 05:26.867 --> 05:28.627 methanol and HF. 05:28.633 --> 05:31.733 But the acidity of HF is well-known. 05:31.733 --> 05:38.533 It's 370.424 kcal per mole with this uncertainty. 05:38.533 --> 05:44.173 And so it turns out that these two numbers give you the 05:44.167 --> 05:49.197 equilibrium constant, and this is going to give you the gas 05:49.200 --> 05:49.870 phase acidity. 05:49.867 --> 05:54.467 So by making the equilibrium constant, Professor Bierbaum 05:54.467 --> 05:56.867 has measured the acidity of this species. 06:01.833 --> 06:04.633 The way to think about this now, to use acidity, here's 06:04.633 --> 06:06.603 what the gas-phase acidity is. 06:06.600 --> 06:10.370 Remember, she really has this number in the gas phase. 06:10.367 --> 06:12.667 You know, in the gas phase, these molecules are never 06:12.667 --> 06:17.197 going to dissociate into ions, because you've got to 06:17.200 --> 06:18.630 deal with Coulomb's law. 06:18.633 --> 06:22.303 So you're talking about maybe 300, 400 kcal per mole. 06:22.300 --> 06:24.500 So it's a whopping amount of energy. 06:24.500 --> 06:29.170 So the way to think about this is, to get that ion, you have 06:29.167 --> 06:32.297 to break the OH bond. 06:32.300 --> 06:37.270 Then you have to somehow measure the electron affinity. 06:37.267 --> 06:41.327 That gives you the energy of the negative ion here. 06:41.333 --> 06:46.473 And the ionization energy of a hydrogen atom is how you 06:46.467 --> 06:47.727 get the proton. 06:47.733 --> 06:51.933 And here, this is the easiest way I think about this. 06:51.933 --> 06:53.533 This acidity-- 06:53.533 --> 06:55.173 you want to get those ions. 06:55.167 --> 06:57.027 The first thing you've got to do is reach in with a pair of 06:57.033 --> 07:00.673 scissors and cut this bond. 07:00.667 --> 07:02.367 So you've got to pay that energy. 07:02.367 --> 07:04.097 You've also got to give me the ionization 07:04.100 --> 07:05.500 energy of hydrogen atom. 07:05.500 --> 07:07.870 You've got to pay me that, because that 07:07.867 --> 07:09.927 gives you the proton. 07:09.933 --> 07:15.833 And then you take the electron and put it back on the alkoxy 07:15.833 --> 07:17.933 radical, and that's the electron affinity. 07:17.933 --> 07:19.203 So it turns out-- 07:22.200 --> 07:23.170 Here, 07:23.167 --> 07:24.097 this is what we're after. 07:24.100 --> 07:25.300 We want this bond energy. 07:25.300 --> 07:28.770 And this will be the energy for that bond only. 07:28.767 --> 07:33.667 And so the electron affinity for hydrogen atom is known to 07:33.667 --> 07:35.227 some pornographic detail. 07:35.233 --> 07:37.803 You couldn't imagine what's been done to this poor atom. 07:37.800 --> 07:40.400 This is done to like 80 digits. 07:40.400 --> 07:43.600 So turns out the only thing you've got to do is now, you 07:43.600 --> 07:45.530 now have to measure the electron 07:45.533 --> 07:47.803 affinity of the radical. 07:47.800 --> 07:51.400 So how are you going to do that? 07:51.400 --> 07:58.430 So this is an experiment that's done actually here by 07:58.433 --> 08:03.033 Professor Mark Johnson at Yale University, and it's done a 08:03.033 --> 08:05.803 bit by people in Boulder, Colorado. 08:05.800 --> 08:06.730 Here's what you do. 08:06.733 --> 08:10.033 You literally take a vapor of these negative ions. 08:10.033 --> 08:12.573 And if you take a vapor of the negative ions, 08:12.567 --> 08:14.467 you make a fast beam. 08:14.467 --> 08:16.767 You cross this with a laser. 08:16.767 --> 08:19.867 I know the energy of the laser precisely. 08:19.867 --> 08:23.097 So what you do is, when the laser interacts with the 08:23.100 --> 08:27.000 negative ions, you'll eject electrons, and you catch them 08:27.000 --> 08:28.770 in a hemispherical analyzer. 08:28.767 --> 08:30.897 You literally measure the kinetic energy. 08:30.900 --> 08:32.800 So this is the kinetic energy. 08:32.800 --> 08:33.430 So here. 08:33.433 --> 08:35.303 This is easy. 08:35.300 --> 08:37.900 If you know what the energy going in is, and you know what 08:37.900 --> 08:40.270 the energy coming out is, you've measured those two 08:40.267 --> 08:42.897 things, and the difference is the binding energy. 08:42.900 --> 08:46.930 So here's the negative ion. 08:46.933 --> 08:51.473 When the electromagnetic wave comes blazing in and strikes 08:51.467 --> 08:54.727 it, what happens is, here's the laser energy. 08:54.733 --> 08:58.933 So the molecule literally interacts with the laser, and 08:58.933 --> 09:02.773 an electron's knocked off, and what you're going to do, is 09:02.767 --> 09:04.067 you're going to measure the red arrow. 09:04.067 --> 09:07.127 This is the kinetic energy of the photoelectron. 09:07.133 --> 09:10.403 So if you measure what comes out, then the difference is 09:10.400 --> 09:11.730 the binding energy. 09:11.733 --> 09:17.703 So it turns out that this is the essential experiment you 09:17.700 --> 09:19.770 have to do. 09:19.767 --> 09:21.067 There's a bunch of details you've got to 09:21.067 --> 09:22.197 pay attention to. 09:22.200 --> 09:26.430 If the product radical is vibrating, then the 09:26.433 --> 09:29.133 photoelectron kinetic energy will be smaller than the 09:29.133 --> 09:31.703 measured binding energy. 09:31.700 --> 09:33.600 And these are just a bunch of words. 09:33.600 --> 09:35.630 Let me just show you what you do. 09:35.733 --> 09:36.873 This is it. 09:39.633 --> 09:42.373 Jesus, we did this like thirty years ago. 09:42.367 --> 09:45.427 Christ, I'm an old guy. 09:45.433 --> 09:47.573 When you do this, what you do is you take a-- 09:51.633 --> 09:52.773 right here. 09:52.767 --> 09:54.667 So what you're going to do is, you're going to measure the 09:54.667 --> 09:56.427 kinetic energy of the electrons coming out. 09:56.433 --> 09:57.733 So we're making a plot of the 09:57.733 --> 09:59.733 photoelectron kinetic energy. 09:59.733 --> 10:04.473 Here, let me just show, the laser is 488. 10:04.467 --> 10:06.397 It's a beautiful robin's egg blue. 10:06.400 --> 10:08.830 Extremely bright laser. 10:08.833 --> 10:13.033 And 488 nanometers is 2.540 electron volts. 10:13.033 --> 10:13.503 So here. 10:13.500 --> 10:14.430 Think about this. 10:14.433 --> 10:16.473 This is the photoelectron kinetic energy with electrons 10:16.467 --> 10:17.167 coming out. 10:17.167 --> 10:22.167 No electrons can come out with more than 2.54 eV, because 10:22.167 --> 10:24.427 that's all I've got to put in. 10:24.433 --> 10:27.503 So the first time you see electronic, counts-- 10:27.500 --> 10:28.770 this is electron counts-- 10:28.767 --> 10:33.497 is at about 1 eV. When you actually measure it, it's 10:33.500 --> 10:39.370 measured to be 0.968 eV. And so the way you get the 10:39.367 --> 10:43.497 electron affinity, is if you put 2.54 eV in, and you 10:43.500 --> 10:50.330 measure 0.968 coming out, then the difference is 1.572, plus 10:50.333 --> 10:51.873 or minus 4 milli electron volts. 10:51.867 --> 10:54.727 And that's how you do it. 10:54.733 --> 10:57.803 This is detachment to the ground state 10:57.800 --> 10:59.830 of the methoxy dot. 10:59.833 --> 11:02.573 This is one vibration in the methoxy dot. 11:02.567 --> 11:05.297 This is two vibrations, this is three vibrations. 11:05.300 --> 11:06.930 Can you see how cool this is? 11:06.933 --> 11:09.103 You can actually take a vibrational spectrum. 11:09.100 --> 11:11.870 You're looking at the vibrations in a radical. 11:11.867 --> 11:13.127 Well, that's not hard-- 11:13.133 --> 11:14.033 that's not easy to do. 11:14.033 --> 11:15.803 Because you don't have a lecture bottle of radicals. 11:15.800 --> 11:19.100 So this is a very powerful experiment on the one day of 11:19.100 --> 11:20.970 the month when it works. 11:20.967 --> 11:22.497 I'll not kid you. 11:22.500 --> 11:25.330 These experiments of Professor Bierbaum's, 11:25.333 --> 11:25.903 you spend most of 11:25.900 --> 11:29.170 your time with the hardware, trying to make sure the 11:29.167 --> 11:30.867 electronics are stable and what not. 11:30.867 --> 11:33.797 And then when you're running, these people basically are 11:33.800 --> 11:36.970 dancing around the machine nude with tambourines, just 11:36.967 --> 11:38.997 trying to keep the machine stable long 11:39.000 --> 11:40.300 enough to get a spectrum. 11:40.300 --> 11:43.230 But when it works, you're going to get 11:43.233 --> 11:44.433 a number very clean. 11:44.433 --> 11:46.303 And you see how precise this is? 11:46.300 --> 11:49.970 I mean, this is a very nice measurement. 11:49.967 --> 11:54.527 So we can now do what we're going to do. 11:54.533 --> 11:59.373 If Bierbaum has the acidity, and you know the electron 11:59.367 --> 12:02.827 affinity, and you know the ionization energy of hydrogen 12:02.833 --> 12:06.703 atom, so here are these numbers. 12:06.700 --> 12:09.600 When you put these things in, you get out that the bond 12:09.600 --> 12:12.370 energy is about a 105 kcal per mole. 12:12.367 --> 12:15.167 And this is the bond energy of methanol in the innergalactic 12:15.167 --> 12:18.367 space with nobody else around. 12:18.367 --> 12:21.267 And all of these people who like to think they can 12:21.267 --> 12:23.697 calculate everything by using all these quantum mechanical 12:23.700 --> 12:26.870 programs, now this is the number they have to get. 12:26.867 --> 12:28.397 There is no place to hide. 12:28.400 --> 12:31.170 This is the cleanly measured value. 12:35.000 --> 12:38.130 No experimental system is perfect. 12:38.133 --> 12:43.303 So for example, problems you can have. I just showed you 12:43.300 --> 12:45.170 how to measure the OH bond. 12:45.167 --> 12:47.567 Suppose you want to measure the CH bond. 12:47.567 --> 12:50.827 Well, this will never work! 12:50.833 --> 12:53.633 Because the negative cycle will never work. 12:53.633 --> 12:54.173 Why? 12:54.167 --> 12:58.527 Because when you take any base that you apply to this, the 12:58.533 --> 13:01.003 base is always going to take off the most acidic proton. 13:01.000 --> 13:03.770 Well, the most acidic proton is one off the OH, because you 13:03.767 --> 13:07.667 get the negative on with the electron on the oxygen. 13:07.667 --> 13:09.427 That's good. 13:09.433 --> 13:12.873 If you have a base that you try to pull a proton off the 13:12.867 --> 13:17.027 carbon, the electron is going to be on the carbon atom, and 13:17.033 --> 13:18.533 that's bad. 13:18.533 --> 13:20.203 Oxygen's more electronegative. 13:20.200 --> 13:22.500 It'll hold it much tighter. 13:22.500 --> 13:27.970 So turns out the negative ions are not going to be a useful 13:27.967 --> 13:29.867 way to do this. 13:29.867 --> 13:31.567 And of course, if you were going to apply the negative-ion 13:31.567 --> 13:35.527 cycle, then you'd have to measure the acidity of this 13:35.533 --> 13:38.173 proton, then we'd have to measure the electron affinity 13:38.167 --> 13:39.327 of this radical. 13:39.333 --> 13:40.833 Does everybody see that this radical-- 13:40.833 --> 13:42.733 this is hydroxy methyl radical-- 13:42.733 --> 13:44.303 is different than methoxy? 13:44.300 --> 13:47.570 Because the dot sits on the carbon, not on the oxygen, so 13:47.567 --> 13:48.897 it's a different radical. 13:48.900 --> 13:51.070 So if you can't make the ion, then we can't do our 13:51.067 --> 13:53.297 measurements, and we're dead. 13:53.300 --> 13:55.330 Not to worry. 13:55.333 --> 13:58.903 There's other techniques you can do. 13:58.900 --> 14:06.070 My friend David Gutman does radical kinetics. 14:06.067 --> 14:09.697 And so a thing you can do is you can make chlorine atoms. 14:09.700 --> 14:15.030 And when you make chlorine atoms in a flow tube, he uses 14:15.033 --> 14:18.133 photoionization mass spec to monitor the products. 14:18.133 --> 14:21.773 And so he can measure K1, and he can measure K minus 1. 14:21.767 --> 14:22.597 So he gets to equal-- 14:22.600 --> 14:25.600 PROFESSOR MCBRIDE: Can you explain what a flow tube is? 14:25.600 --> 14:30.330 PROFESSOR ELLISON: A flow tube is a beautiful device that's a 14:30.333 --> 14:32.033 meter long. 14:32.033 --> 14:36.173 It's my fist, ten centimeters in diameter. 14:36.167 --> 14:40.327 And Bierbaum has flowing through this a tremendous flow 14:40.333 --> 14:42.003 of helium gas. 14:42.000 --> 14:46.070 And so when you make ions, the ions are made up here in the 14:46.067 --> 14:46.997 discharge, and then-- 14:47.000 --> 14:48.700 PROFESSOR MCBRIDE: Wha's the pressure in there? 14:48.700 --> 14:51.030 PROFESSOR ELLISON: The pressure will be about a torr. 14:51.033 --> 14:55.833 And so it turns out that it's mostly helium, and you have a 14:55.833 --> 14:58.673 few millitorr of the reagents that you've got. 14:58.667 --> 15:00.527 You have a quadrupole mass spec. 15:00.533 --> 15:03.833 The quadrupole mass spec, of course, can't operate in a 15:03.833 --> 15:10.873 millitorr, so there's some clever pumping that you have 15:10.867 --> 15:13.767 to sample the output of the flow tube. 15:13.767 --> 15:16.367 So the quadrupole mass spec only looks at the ions. 15:16.367 --> 15:19.897 So if you have a reaction that occurs in here, one ion would 15:19.900 --> 15:22.270 go away, and another one would come up. 15:22.267 --> 15:25.597 And you can monitor this with a quadrupole mass spec. 15:25.600 --> 15:28.030 Remember, the way the ions get downstream is they're carried 15:28.033 --> 15:29.603 along by the helium. 15:29.600 --> 15:33.070 And what's true in a flow tube is, the distance equals the 15:33.067 --> 15:34.327 rate times the time. 15:34.333 --> 15:36.573 So if you have a shorter distance, you have a shorter 15:36.567 --> 15:37.327 reaction time. 15:37.333 --> 15:38.803 If you have a longer distance, you have a 15:38.800 --> 15:39.870 longer reaction time. 15:39.867 --> 15:41.797 And if you measure that variation, you 15:41.800 --> 15:42.530 can get a rate constant. 15:42.533 --> 15:45.633 PROFESSOR MCBRIDE: How do you change the distance? 15:45.633 --> 15:47.903 PROFESSOR ELLISON: It turns out that you can change the 15:47.900 --> 15:52.670 distance by admitting your reagent through 15:52.667 --> 15:53.827 a tiny little tube. 15:53.833 --> 15:56.403 And this tube is the cutest little thing you 15:56.400 --> 15:57.700 ever saw in your life. 15:57.700 --> 16:00.170 It slides on a little wire. 16:00.167 --> 16:07.327 And they literally, like a gorilla, they'll set the 16:07.333 --> 16:13.833 ejection tube at a certain space, and then what they'll 16:13.833 --> 16:16.903 do, is they'll systematically vary this by simply 16:16.900 --> 16:17.900 pulling this back. 16:17.900 --> 16:20.530 Then they'll measure the ratios of these rates. 16:20.533 --> 16:23.133 PROFESSOR MCBRIDE: We talked earlier about Robert Hooke 16:23.133 --> 16:26.433 making a vacuum pump to lower pressure. 16:26.433 --> 16:28.303 So is that the kind, do you have somebody down, 16:28.300 --> 16:30.800 in the basement pumping on this or how do you get the vacuum? 16:30.800 --> 16:31.370 PROFESSOR ELLISON: No, it turns out-- 16:31.367 --> 16:31.927 PROFESSOR MCBRIDE: That's a lot 16:31.933 --> 16:32.803 of helium you're putting through. 16:32.800 --> 16:33.330 PROFESSOR ELLISON: Sure. 16:33.333 --> 16:33.703 OK. 16:33.700 --> 16:39.570 So Professor Bierbaum uses a set of pumps which 16:39.567 --> 16:41.697 are as big as I am. 16:41.700 --> 16:43.970 They're roots blowers. 16:43.967 --> 16:48.627 These pumps will pump just a staggering quantity of gas, 16:48.633 --> 16:53.573 like 500 liters a second, at this pressure. 16:53.567 --> 16:55.567 These pumps-- 16:55.567 --> 16:57.867 I'm just telling you words-- 16:57.867 --> 17:00.727 one of the uses of these pumps are to pump grain in grain 17:00.733 --> 17:02.003 elevators in Kansas. 17:02.000 --> 17:04.330 Have you ever been to some dreadful place like Kansas? 17:04.333 --> 17:08.703 I mean, there's 10,000 of these silos. 17:08.700 --> 17:13.000 And so the grain is pumped around in these, with these 17:13.000 --> 17:13.830 huge pumps. 17:13.833 --> 17:17.033 So she has two of these in the basement. 17:17.033 --> 17:21.633 So it's a very hard experiment to do. 17:21.633 --> 17:24.073 So you can also do radicals in this. 17:24.067 --> 17:27.667 And let me just tell you Gutman's experiment. 17:27.667 --> 17:29.567 He's going to measure Kequi 17:29.567 --> 17:31.897 and so he's going to measure the reaction, from the 17:31.900 --> 17:34.400 equilibrium constant. From the temperature variation of the 17:34.400 --> 17:40.130 equilibrium constant, he's going to get the reaction 17:40.133 --> 17:40.833 energy of this. 17:40.833 --> 17:43.703 And the reaction energy of this radical reaction is, 17:43.700 --> 17:46.430 you're going to have to pay the bond energy, this CH bond 17:46.433 --> 17:48.073 energy, and you're going to get the bond 17:48.067 --> 17:50.367 energy of HCI back. 17:50.367 --> 17:51.627 I now have to tell you something. 17:51.633 --> 17:55.973 The bond energy of HCl is known to be 103 kcal per mole. 17:55.967 --> 17:59.297 Remember, I told you the bond energy for methanol is 104. 17:59.300 --> 18:04.570 So the chloride atoms, if they hit the hydrogen on the OH 18:04.567 --> 18:06.997 group, if they hit it, they'll just bounce off, because they 18:07.000 --> 18:08.800 don't have enough energy to do this. 18:08.800 --> 18:13.270 So they're only going to pull the hydrogens 18:13.267 --> 18:14.967 off the methyl group. 18:14.967 --> 18:18.797 So when you do that, if you do the analysis, you can get that 18:18.800 --> 18:24.970 the CH bond on methanol is 96 kcal per mole. 18:24.967 --> 18:27.267 And on the days when it works, you can 18:27.267 --> 18:28.997 get this very precisely. 18:29.000 --> 18:31.400 So those are two of the bond energies that you 18:31.400 --> 18:34.800 can get from methanol. 18:34.800 --> 18:39.130 So you might wonder, what's the CO bond in methanol? 18:39.133 --> 18:41.433 In other words, you're literally going to take the 18:41.433 --> 18:45.603 methanol molecule, and you'll karate-chop it in the center, 18:45.600 --> 18:47.300 and you just want to cut it in two. 18:47.300 --> 18:52.700 So that means I've got to measure the energy of the 18:52.700 --> 18:55.400 methyl radicals and the hydroxyl radicals. 18:55.400 --> 19:00.830 So it turns out, this is a straightforward thing to do. 19:00.833 --> 19:05.033 Turns out that if you want to look at this, this bond 19:05.033 --> 19:10.273 energy, to get that heat of formation...Here, I need to get 19:10.267 --> 19:10.997 methyl radicals. 19:11.000 --> 19:13.870 So to get methyl radicals, you actually have to measure the 19:13.867 --> 19:14.927 bond energy of methane. 19:14.933 --> 19:18.133 Because that's the bond energy of methane is the heat of 19:18.133 --> 19:20.503 formation of methyl radicals, heat of formation of hydrogen, 19:20.500 --> 19:22.230 minus that of methane. 19:22.233 --> 19:26.903 So photoionization mass spec or reaction kinetics both 19:26.900 --> 19:28.700 measure the bond energy of methane to be 19:28.700 --> 19:32.000 104.99 kcal per mole. 19:32.000 --> 19:34.670 The bond energy of hydrogen, H atom, comes from the 19:34.667 --> 19:37.197 dissociation energy of H2. 19:37.200 --> 19:39.470 So there's classical tables. 19:39.467 --> 19:43.327 These guys, Mr. Pedley and his friends, there's 3,000 of 19:43.333 --> 19:45.303 these bond energies that these guys anally 19:45.300 --> 19:48.970 have put in this book. 19:48.967 --> 19:53.827 So it turns out that if you have these guys, you now use 19:53.833 --> 19:56.603 the heat of formation of methyl radical. 19:56.600 --> 20:00.500 I also need to tell you that the bond energy of water gives 20:00.500 --> 20:02.030 you the heat of formation of methyl 20:02.033 --> 20:04.473 radical-- of hydroxyl radical. 20:04.467 --> 20:07.497 So turns out if I know hydroxyl radical, and I know 20:07.500 --> 20:10.300 methyl radical, then Pedley et al will give you the heat of 20:10.300 --> 20:12.170 formation of methanol. 20:12.167 --> 20:14.697 So this is the other thing I'm going to need. 20:14.700 --> 20:18.670 So turns out that this bond energy is equal to heat of 20:18.667 --> 20:22.067 formation of methyl radical, plus OH radical, 20:22.067 --> 20:23.927 minus that of methanol. 20:23.933 --> 20:26.873 And so this comes from water, that comes from bond energy of 20:26.867 --> 20:29.227 methane, dissociation of methane. 20:29.233 --> 20:31.333 And this is Mr. Pedley. 20:31.333 --> 20:34.333 So that's actually the weakest bond in the molecule. 20:34.333 --> 20:36.973 The weakest bond in the molecule is the CO bond. 20:36.967 --> 20:44.227 So you can actually work all of three of these bonds out by 20:44.233 --> 20:45.903 going through a procedure. 20:45.900 --> 20:49.000 Me and a whole bunch of other really smart people have 20:49.000 --> 20:54.000 measured a large number of these molecules, and these are 20:54.000 --> 20:55.430 the bond energies. 20:55.433 --> 21:01.733 There's all sorts of complicated heats of formation 21:01.733 --> 21:03.973 that you can use. 21:03.967 --> 21:08.327 Let me just talk here at the end, for the last part of 21:08.333 --> 21:11.573 this, about trying to compare these things. 21:14.133 --> 21:17.303 Professor McBride is typically going on like a broken record. 21:17.300 --> 21:19.630 We always try to say, how do you know what you've done? 21:22.367 --> 21:24.067 Which means to say-- 21:24.067 --> 21:24.467 Here. 21:24.467 --> 21:25.167 I'm not kidding you. 21:25.167 --> 21:26.597 It's very easy to make a mistake. 21:26.600 --> 21:28.700 If you get any of these calibrations wrong, or any of 21:28.700 --> 21:32.600 these little cycles are done in an incorrect manner, it's 21:32.600 --> 21:37.330 very easy for you to have an uncertainty. 21:37.333 --> 21:39.033 Indeed, let me go back. 21:39.033 --> 21:43.873 I need to make one point I wasn't smart enough to do 21:43.867 --> 21:45.567 where I had this acidity. 21:45.567 --> 21:46.827 Here. 21:50.833 --> 21:53.103 This bond energy that we're going to measure-- 21:53.100 --> 21:55.330 OK, we're going to get this through a cycle. 21:55.333 --> 21:59.173 And to do this cycle, we have to do two difficult 21:59.167 --> 22:00.497 experiments. 22:00.500 --> 22:02.500 Bierbaum has to measure the acidity. 22:02.500 --> 22:03.770 It's a very large number. 22:03.767 --> 22:06.127 That's 380 kcal per mole. 22:06.133 --> 22:09.073 And the electron affinity is known. 22:09.067 --> 22:10.997 The ionization energy of hydrogen atoms is known. 22:11.000 --> 22:12.200 But you have to measure the electron 22:12.200 --> 22:15.270 affinity for this radical. 22:15.267 --> 22:19.397 So this number comes from a cycle where you're adding and 22:19.400 --> 22:21.430 subtracting large numbers. 22:21.433 --> 22:23.073 And you're smart guys. 22:23.067 --> 22:23.727 You know this. 22:23.733 --> 22:27.633 If you have a number that you're after, and there's a 22:27.633 --> 22:30.233 cycle that you go through, and you're taking differences of 22:30.233 --> 22:31.573 large numbers 22:31.567 --> 22:37.297 any fault, any mistake that's made here, that error is going 22:37.300 --> 22:39.930 to be in this bond energy, or any error that comes in this 22:39.933 --> 22:41.303 measurement. 22:41.300 --> 22:45.100 There's a famous chemist who's English, whose name is Colson. 22:45.100 --> 22:50.030 And Colson used to say, procedure is like weighing a 22:50.033 --> 22:52.503 captain on the ship by weighing the ship with and 22:52.500 --> 22:54.400 without the captain. 22:54.400 --> 22:54.730 Here. 22:54.733 --> 22:55.973 So you have an aircraft carrier. 22:55.967 --> 22:56.267 OK. 22:56.267 --> 22:57.367 You're a smart guy. 22:57.367 --> 22:58.397 You get a pair of scales. 22:58.400 --> 23:01.470 And you know you have to measure this aircraft carrier, 23:01.467 --> 23:02.967 the weight of this very precisely. 23:02.967 --> 23:05.397 And then you put a little guy on top, and then the weight's 23:05.400 --> 23:07.400 going to change just a titch. 23:07.400 --> 23:09.670 And your measurements have to be so precise you 23:09.667 --> 23:10.967 can pick this up. 23:10.967 --> 23:15.267 So on the days when it works, you can really 23:15.267 --> 23:16.297 get these bond energies. 23:16.300 --> 23:20.530 But these are not easy experiments to do. 23:20.533 --> 23:28.433 Let me talk here about these bond energies. 23:28.433 --> 23:30.833 We've done several of these things. 23:30.833 --> 23:38.133 You might guess that if you have an alcohol-- 23:38.133 --> 23:41.333 I did methanol, this is the OH bond in methanol-- 23:41.333 --> 23:43.503 you might hope that the OH bond in ethanol 23:43.500 --> 23:44.800 would be the same. 23:44.800 --> 23:49.930 And it's exactly the same within our uncertainty. 23:49.933 --> 23:51.733 If you go to-- 23:51.733 --> 23:55.573 this is isopropyl alcohol, this is t-butyl alcohol. 23:55.567 --> 23:58.767 t-butyl alcohol is a little bit larger, but you can see, 23:58.767 --> 24:04.897 amongst friends, it's all about 104, 105 kcal per mole. 24:04.900 --> 24:09.970 When you go to measure something like phenol-- 24:09.967 --> 24:12.797 this is an OH bond in phenol, but this is only 24:12.800 --> 24:14.500 like 86 kcal per mole. 24:14.500 --> 24:17.130 And you go, Christ, what's wrong here? 24:17.133 --> 24:19.673 Well, this is no regular alcohol. 24:22.333 --> 24:24.103 Here, I drew this. 24:24.100 --> 24:29.730 If you break the bond in methanol, you get a hydrogen 24:29.733 --> 24:31.303 atom, and you get methoxy dots. 24:31.300 --> 24:35.400 And the dot is stuck on the oxygen atom. 24:35.400 --> 24:39.570 But if you pull a proton off phenol, now that 24:39.567 --> 24:42.527 dot is not on the oxygen. 24:42.533 --> 24:44.373 It's actually delocalized around. 24:44.367 --> 24:46.597 It interacts with the pi system. 24:46.600 --> 24:51.730 And McBride's probably drawn you some of these resonance 24:51.733 --> 24:55.473 forms. Or you can talk about the interaction of this extra 24:55.467 --> 24:58.597 electron with the pi cloud. 24:58.600 --> 25:02.670 This is a catastrophic change. 25:02.667 --> 25:04.797 What this is, like 20 kcal per mole. 25:04.800 --> 25:05.700 That's a volt. 25:05.700 --> 25:09.670 So it's a lot easier for you to remove a hydrogen atom from 25:09.667 --> 25:12.327 phenol than it is from any alcohol. 25:16.833 --> 25:18.673 We've also done a bunch of peroxides. 25:23.733 --> 25:25.873 Remember, here's hydrogen peroxide, here's methyl 25:25.867 --> 25:29.627 hydroperoxide, here's ethyl hydroperoxide. 25:29.633 --> 25:32.473 These, again, look like OH bonds. 25:32.467 --> 25:32.997 Here. 25:33.000 --> 25:34.470 You're also smart people. 25:34.467 --> 25:36.097 You know that these peroxides 25:36.100 --> 25:38.030 they're very reactive compounds. 25:38.033 --> 25:40.403 The reason my daughter's a blonde is because of this. 25:40.400 --> 25:43.300 I mean, you can buy a bottle of this, and only-- 25:43.700 --> 25:47.000 Here, let's see 25:47.000 --> 25:50.000 There's a difference between chemistry and, say, other 25:50.000 --> 25:54.730 subjects, in that these molecules are real. 25:54.733 --> 25:58.633 When we go to do this... Here. My daughter would get... 25:58.633 --> 26:01.903 You could buy a bottle of peroxide in the pharmacy. 26:01.900 --> 26:02.730 It's 5%. 26:02.733 --> 26:06.303 So it's 5% hydrogen peroxide, and 95% water. 26:06.300 --> 26:08.770 So we have to make a beam of these things. 26:08.767 --> 26:13.097 So there's clever ways that if you can have these compounds, 26:13.100 --> 26:16.600 and you can actually distill them, then you can make 99% 26:16.600 --> 26:19.000 hydrogen peroxide. 26:19.000 --> 26:21.300 The hydrogen peroxide, of course, is extremely reactive. 26:21.300 --> 26:22.200 Why is it reactive? 26:22.200 --> 26:25.300 It's because the two oxygens are held together by a single 26:25.300 --> 26:27.370 bond, and you have all these electrons that are crammed 26:27.367 --> 26:28.997 right on top of each other. 26:29.000 --> 26:34.230 So the bond energy of the O-O bond is actually quite weak. 26:34.233 --> 26:36.803 So it's a very good oxidizer. 26:36.800 --> 26:41.470 And so turns out, I've actually... 26:41.467 --> 26:43.267 we had a bottle of about 99% 26:43.267 --> 26:44.167 percent of this stuff. 26:44.167 --> 26:46.427 And I'm talking about this with my students. 26:46.433 --> 26:48.373 And I'm not very skillful. 26:48.367 --> 26:51.497 And so it turns they maybe had about half a 26:51.500 --> 26:53.030 milliliter of this. 26:53.033 --> 26:56.403 As long as hydrogen peroxide is in glass or 26:56.400 --> 26:58.170 plastic, it's fine. 26:58.167 --> 26:59.697 Nothing's going to happen. 26:59.700 --> 27:03.800 You can handle it safely. 27:03.800 --> 27:07.030 But it will oxidize any carbon that it gets to. 27:07.033 --> 27:08.773 So alas, I dropped it. 27:08.767 --> 27:12.127 And when I dropped it, it bounced once on the floor, and 27:12.133 --> 27:13.203 then it broke. 27:13.200 --> 27:17.270 And when it broke, when the glass came down and broke, 27:17.267 --> 27:19.367 it went, fuff! 27:19.367 --> 27:22.267 And there's a big orange spot around. 27:22.267 --> 27:25.667 And what happened was, all the dirt and stuff on the floor 27:25.667 --> 27:26.927 was oxidized immediately! 27:26.933 --> 27:28.633 Just gone. 27:28.633 --> 27:32.203 So if you have a solution of-- 27:32.200 --> 27:34.600 Here, you think I'm kidding. 27:34.600 --> 27:37.600 You have a 100% solution of something like this, you take 27:37.600 --> 27:39.500 a little bunny rabbit with the ears and sort of 27:39.500 --> 27:41.030 lower this thing in-- 27:41.033 --> 27:44.273 this thing is just simply torn to pieces. 27:44.267 --> 27:46.827 Then you pull this thing out, there's just bones. 27:46.833 --> 27:51.503 I mean, this is tremendously reactive! 27:51.500 --> 27:53.670 So all of these things, you have to handle ‘em, and you've 27:53.667 --> 27:55.527 got to get them into your spectrometer. 27:55.533 --> 27:56.573 But OK. 27:56.567 --> 27:59.367 So when you do this, you see the OH bonds-- 27:59.367 --> 28:02.927 see the dots here on this? 28:02.933 --> 28:04.733 This is 88 kcal per mole. 28:04.733 --> 28:07.473 This is a lot different than these guys. 28:07.467 --> 28:10.197 And of course, the one that you're really 28:10.200 --> 28:13.230 interested in is water. 28:13.233 --> 28:16.303 The bond energy for water is 118. 28:16.300 --> 28:20.470 And that goes to OH dot and H atom. 28:20.467 --> 28:24.227 This is an important number. 28:24.233 --> 28:28.503 And remember, water covers 70% of the earth's surface. 28:28.500 --> 28:30.170 Here, you're making a list of what are 28:30.167 --> 28:31.527 the most stable compounds 28:31.533 --> 28:34.073 that God made, it's N2 in the air. 28:34.067 --> 28:37.067 80% of the air we're breathing is N2. 28:37.067 --> 28:38.397 N2 has got a triple bond. 28:38.400 --> 28:39.470 It's indestructible. 28:39.467 --> 28:41.127 Very, very stable. 28:41.133 --> 28:43.503 The sand on beaches. 28:43.500 --> 28:48.000 I mean, the silicon dioxide, the sand, is just like a rock. 28:48.000 --> 28:50.400 I mean, it is a rock. 28:50.400 --> 28:53.200 And then the other thing is water. 28:53.200 --> 28:55.800 70% of the earth's surface. 28:55.800 --> 28:58.900 And the reason it's so stable is, if you want to break this 28:58.900 --> 29:02.230 apart to radicals, you've got to give me 118 kcal per mole. 29:02.233 --> 29:05.033 That's a whopping amount of energy. 29:05.033 --> 29:05.673 Here. 29:05.667 --> 29:09.467 And so you notice, if you just replace this with an 29:09.467 --> 29:11.567 ethyl group, OK? 29:11.567 --> 29:12.867 So you make ethanol. 29:12.867 --> 29:17.067 So the bond energy's going to drop by almost a volt to 104 29:17.067 --> 29:19.397 kcal per mole. 29:19.400 --> 29:20.900 Here. 29:20.900 --> 29:23.400 Imagine you have a swimming pool. 29:23.400 --> 29:24.570 So it's a swimming pool. 29:24.567 --> 29:26.397 Johnny Depp is talking to somebody next to 29:26.400 --> 29:27.300 the swimming pool. 29:27.300 --> 29:28.470 Only instead of the swimming pool, you have 29:28.467 --> 29:29.827 water, you have ethanol. 29:29.833 --> 29:31.173 It's vodka in there. 29:31.167 --> 29:33.567 So Johnny Depp takes a drag on a cigarette, and as he's 29:33.567 --> 29:36.327 talking to Angelina Jolie, he flicks the thing over. 29:36.333 --> 29:39.703 And the split second this hits the pool, there's a flame like 29:39.700 --> 29:41.500 180 meters high. 29:41.500 --> 29:44.030 Because the ethanol ignites! 29:44.033 --> 29:45.603 It burns. 29:45.600 --> 29:48.200 If it's in water, the cigarette goes out. 29:48.200 --> 29:54.930 So this bond energy-- if it's a real stable compound, this 29:54.933 --> 29:56.803 has consequences. 29:56.800 --> 29:57.130 OK. 29:57.133 --> 30:00.303 The last thing I'll tell you is...Here. 30:00.300 --> 30:04.370 These are the bond energies I just told you for methanol. 30:04.367 --> 30:05.927 This is the OH bond. 30:05.933 --> 30:07.433 This is the CH bond. 30:07.433 --> 30:09.573 The weakest bond is the CO bond. 30:09.567 --> 30:12.167 These are these numbers in kcal per mole. 30:12.167 --> 30:14.327 It's always interesting. 30:14.333 --> 30:18.273 If you knew what these bond energies are, what are the 30:18.267 --> 30:20.327 bond energies for the radicals? 30:20.333 --> 30:25.233 So if I reach in and cut a bond here and I make methoxy dot, 30:25.233 --> 30:31.973 if I make methoxy dot, now the bond energy for the CH bond-- 30:31.967 --> 30:34.527 Here, I can use the meter stick-- 30:34.533 --> 30:40.503 the CH bond, which used to be 96 kcal per mole, drops to 22. 30:40.500 --> 30:41.730 You can see why. 30:41.733 --> 30:45.133 The minute you cut the bond here, the hydrogen atom 30:45.133 --> 30:48.573 leaves, but this dot couples with that dot, and you've got 30:48.567 --> 30:49.667 formaldehyde. 30:49.667 --> 30:52.297 Nice, stable compound. 30:52.300 --> 30:55.930 And the CO bond here is about 90 kcal per mole. 30:55.933 --> 30:58.003 This is about the same thing it is for 30:58.000 --> 31:01.830 the CO bond in methanol. 31:01.833 --> 31:04.773 You go to the other bond, which is hydroxy methyl. 31:04.767 --> 31:07.027 You go to this species. 31:07.033 --> 31:10.803 Again, if you cut the bond off the OH bond, you get a dot 31:10.800 --> 31:13.300 here, and the other dot then combines back here with 31:13.300 --> 31:13.830 formaldehyde. 31:13.833 --> 31:16.603 So now this is 30 kcal per mole, to be 31:16.600 --> 31:19.200 contrasted with 106. 31:19.200 --> 31:22.500 What's interesting is the CO bond, which used 31:22.500 --> 31:26.100 to be 92, goes up. 31:26.100 --> 31:28.100 I don't know why, but it does. 31:28.100 --> 31:29.500 And not by a little bit. 31:29.500 --> 31:31.000 This is almost a volt. 31:31.000 --> 31:35.530 So there's all sorts of interesting patterns you can 31:35.533 --> 31:37.103 have in these bond energies. 31:37.100 --> 31:45.100 And you literally can have...you can look at that 31:45.100 --> 31:48.070 not only these alcohols, but all 31:48.067 --> 31:52.827 sorts of alkyl peroxides and a variety of these things. 31:53.533 --> 31:55.933 OK. Here. 31:55.933 --> 31:57.933 I'm going to finish early, you can see. 31:57.933 --> 31:59.773 PROFESSOR MCBRIDE: There'll be questions. 31:59.767 --> 32:01.727 PROFESSOR ELLISON: So here there's another thing 32:01.733 --> 32:02.933 I want to show you. 32:02.933 --> 32:08.133 And that is, when you talk about what a bond strength is, 32:08.133 --> 32:11.673 it turns out that an early way that people tried to measure 32:11.667 --> 32:13.827 bond strengths would be that you'd consider a 32:13.833 --> 32:14.773 molecule like methane-- 32:14.767 --> 32:16.697 I need my big stick here-- 32:16.700 --> 32:22.430 and you take methane, you can burn it, and you can actually 32:22.433 --> 32:25.703 measure the energy to take this apart to a carbon atom 32:25.700 --> 32:26.930 and four hydrogens. 32:26.933 --> 32:33.433 So Chupka described to you how you would measure the energies 32:33.433 --> 32:36.573 of individual carbon atoms. You can actually work out that 32:36.567 --> 32:42.427 the bond, to break all four bonds in methane is going to 32:42.433 --> 32:46.803 cost you 497.5 kcal per mole. 32:46.800 --> 32:50.070 Since there's four bonds in methane, you'd cross yourself, 32:50.067 --> 32:52.227 think of Jesus, and then just divide by four. 32:52.233 --> 32:55.903 And if you did that, that number divided by four is 99 32:55.900 --> 32:58.200 kcal per mole. 32:58.200 --> 33:00.400 And so you figure, that must be sort of the 33:00.400 --> 33:02.130 average bond energy. 33:02.133 --> 33:05.003 If you go through these cycles, like I just told you, 33:05.000 --> 33:06.900 you can actually measure individually. 33:06.900 --> 33:15.430 The first bond is 104.99 plus or minus 0.03 kcal per mole. 33:15.433 --> 33:17.633 And that's the first bond energy. 33:17.633 --> 33:19.573 That gives you the absolute heat of formation of a 33:19.567 --> 33:20.727 methyl radical. 33:20.733 --> 33:23.933 You can now take methyl radical and 33:23.933 --> 33:25.203 measure the second bond. 33:25.200 --> 33:30.070 Notice the bond energy goes up from 105 to 110. 33:30.067 --> 33:33.967 Then the third one is 101, and the last one 33:33.967 --> 33:35.497 is 90 kcal per mole. 33:35.500 --> 33:37.600 And these guys give you, individually, the heats of 33:37.600 --> 33:40.370 formation of all of these species. 33:40.367 --> 33:44.467 Notice that not a single one of these bond energies equals 33:44.467 --> 33:46.597 that average. 33:46.600 --> 33:50.570 Here it's close, but the uncertainties are such that 33:50.567 --> 33:52.197 it's not quite. 33:52.200 --> 33:55.530 And so using these average bond energies, you've got to 33:55.533 --> 33:57.133 be careful. 33:57.133 --> 33:59.833 The other thing I'll also tell you, if you actually take the 33:59.833 --> 34:03.803 sum of these numbers and add them up, it's 397.5. It's 34:03.800 --> 34:06.200 exactly this. 34:06.200 --> 34:09.830 And this is a testament to the guys who did these 34:09.833 --> 34:10.303 measurements. 34:10.300 --> 34:12.270 These are very hard experiments to do, and that 34:12.267 --> 34:14.067 means that each one of these four numbers is right. 34:14.067 --> 34:16.127 Because you know, this thing has to be right. 34:16.133 --> 34:18.973 The four of these guys have to add to these things. 34:18.967 --> 34:21.727 So here. If the sum of these things is this, that means the 34:21.733 --> 34:23.673 first law of thermodynamics really works. 34:23.667 --> 34:32.227 So this is a very interesting set of experiments to do. 34:32.233 --> 34:32.533 OK. 34:32.533 --> 34:35.033 So here. 34:35.033 --> 34:36.073 I'm going to give you people-- 34:36.067 --> 34:37.497 PROFESSOR MCBRIDE: Let's have some questions. 34:37.500 --> 34:37.700 PROFESSOR ELLISON: OK. 34:37.700 --> 34:41.030 So I'm allowed to show my last little picture, then. 34:41.033 --> 34:43.003 Here. 34:43.000 --> 34:45.500 I'm in Boulder, Colorado, and we're not as sophisticated as 34:45.500 --> 34:46.770 you people here are in New Haven. 34:53.333 --> 34:54.533 So this is me. 34:54.533 --> 34:57.403 Carl Lineberger is the captain of the negative ions. 34:57.400 --> 34:59.900 The smartest guy in the world about doing negative ion 34:59.900 --> 35:01.300 spectroscopy. 35:01.300 --> 35:05.670 Chuck DePuy here is a Yale PhD, is a member of the 35:05.667 --> 35:07.597 National Academy of Sciences. 35:07.600 --> 35:09.430 He's an organic chemist in Boulder. 35:09.433 --> 35:12.073 Eldon Ferguson is the inventor of the flowing afterglow. 35:12.067 --> 35:12.867 It was at NOAA. 35:12.867 --> 35:15.197 The National Oceanic and Atmospheric 35:15.200 --> 35:17.930 Administration in Boulder. 35:17.933 --> 35:22.073 This is Steve Leone, who's one of the most famous chemical 35:22.067 --> 35:23.327 physicists in the United States. 35:23.333 --> 35:24.933 He's now at Berkeley. 35:24.933 --> 35:27.803 He's the head of the Chemical Dynamics Beamline out there. 35:27.800 --> 35:33.600 Zdenek Herman was a postdoc here in the 1960s, and he's at 35:33.600 --> 35:37.330 the Academy of Sciences in Prague. 35:37.333 --> 35:42.503 And this is Roni Bierbaum, who's the master of negative 35:42.500 --> 35:43.670 ion chemistry. 35:43.667 --> 35:46.967 So I've given you about ten minutes early, so I'm happy to 35:46.967 --> 35:57.467 answer any questions that you people may have. 35:57.467 --> 35:57.967 PROFESSOR MCBRIDE: OK. 35:57.967 --> 35:59.467 Do you have any questions or comments? 36:03.533 --> 36:06.303 OK, I have one. 36:06.300 --> 36:07.600 So let's go back to your-- 36:10.867 --> 36:11.797 how do we get out of here? 36:11.800 --> 36:14.970 PROFESSOR ELLISON: Oh, you hit a B? 36:14.967 --> 36:16.797 PROFESSOR MCBRIDE: But I want to go back to the beginning. 36:19.300 --> 36:21.270 Let's, for what it's worth-- 36:27.167 --> 36:28.397 here we go. 36:31.400 --> 36:34.870 That, hold up that spectrum you showed that had vibrational 36:34.867 --> 36:36.097 in here. 36:36.100 --> 36:37.330 PROFESSOR ELLISON: That's right. 36:40.367 --> 36:41.997 Yes, there it is. 36:42.000 --> 36:44.000 PROFESSOR MCBRIDE: Now, do people understand 36:44.000 --> 36:46.700 how this was working? 36:46.700 --> 36:56.130 You put the laser energy in, and you measure this 36:56.133 --> 36:56.503 difference, right? 36:56.500 --> 36:57.730 PROFESSOR ELLISON: That's right. 36:57.733 --> 36:59.533 PROFESSOR MCBRIDE: But sometimes some of the energy 36:59.533 --> 37:01.803 went into vibration of the molecule. 37:01.800 --> 37:06.830 So the energy that came out was smaller, to the extent 37:06.833 --> 37:10.573 that vibration actually went into the molecule. 37:10.567 --> 37:14.167 So here, you say, is when no vibrational energy goes into 37:14.167 --> 37:15.427 the product. 37:17.267 --> 37:19.867 So that's how you know what the lowest energy is. 37:19.867 --> 37:22.027 But here's a peak here. 37:22.033 --> 37:22.833 PROFESSOR ELLISON: Right. 37:22.833 --> 37:25.773 So that comes from the fact that you have a vibrationally 37:25.767 --> 37:27.467 excited negative ion. 37:27.467 --> 37:29.967 The negative ion, instead of being in its ground 37:29.967 --> 37:32.967 vibrational state, has a little bit of energy. 37:32.967 --> 37:35.767 And it will actually be in the CO stretch, is 37:35.767 --> 37:36.967 where this will be. 37:36.967 --> 37:42.497 So if there's energy in the negative ion, then, to go back 37:42.500 --> 37:43.770 to my diagram-- 37:49.367 --> 37:53.297 if you have hot bands, in other words, if some of the 37:53.300 --> 37:58.030 molecules have vibrational energy in this, then the 37:58.033 --> 38:01.003 molecules aren't down here, y equal to zero, but they're 38:01.000 --> 38:04.570 actually populated in higher states here. 38:04.567 --> 38:06.967 So that means that those electrons will take less 38:06.967 --> 38:08.767 kinetic energy to get off. 38:08.767 --> 38:11.827 And you can always spot them, because they'll have a 38:11.833 --> 38:13.103 different frequency. 38:15.200 --> 38:16.430 Here. 38:22.333 --> 38:24.803 You're going to have a set of frequencies here, which will 38:24.800 --> 38:28.000 be a mode in the neutral molecule. 38:28.000 --> 38:31.370 This is the methoxy radical, and this is that of the 38:31.367 --> 38:32.267 negative ion. 38:32.267 --> 38:34.327 And so this is a vibration in the negative ion. 38:34.333 --> 38:36.073 And they'll be different, because the electrons are 38:36.067 --> 38:37.697 different in these things. 38:37.700 --> 38:44.130 So you can guess, when you get to a molecule which gets to be 38:44.133 --> 38:47.733 more complex, like phenoxy radical-- 38:47.733 --> 38:49.133 I talked to you about that-- 38:49.133 --> 38:53.433 phenoxy radical has a lot more atoms. So analyzing this 38:53.433 --> 38:56.303 steadily gets more and more difficult. 38:56.300 --> 38:57.230 But we like to do that. 38:57.233 --> 38:58.873 That's what God put us on this earth for. 39:02.167 --> 39:04.327 You can also guess-- 39:04.333 --> 39:06.203 I'm interested right now in sugars, because I'm interested 39:06.200 --> 39:08.400 in how biomass decomposes. 39:08.400 --> 39:09.970 You know what glucose looks like? 39:09.967 --> 39:14.927 Glucose is a molecule that has many different hydroxyls on 39:14.933 --> 39:17.903 it, and hydroxyls are all slightly different. 39:17.900 --> 39:21.300 So now, instead of making a negative ion like in methoxy-- 39:21.300 --> 39:22.570 I mean, how hard can this be? 39:22.567 --> 39:23.967 You've only got one OH. 39:23.967 --> 39:27.267 What happens if you add ethylene glycol, or if you 39:27.267 --> 39:28.227 take glycerol-- 39:28.233 --> 39:31.333 ethylene glycol has two hydroxyls, glycerol has three, 39:31.333 --> 39:34.903 threose is going to have four, ribose is going to have five. 39:34.900 --> 39:36.730 So now you're going to have to begin to tell which 39:36.733 --> 39:39.433 OH this came from. 39:39.433 --> 39:41.603 So this is going to be a bitch. 39:41.600 --> 39:44.130 But you if you can do this, you would be able to take 39:44.133 --> 39:47.433 these molecules, and you'll be able to break all the bonds in 39:47.433 --> 39:51.003 the order that you'd like to do it. 39:51.000 --> 39:54.730 And that's very interesting to do. 39:54.733 --> 39:58.973 PROFESSOR MCBRIDE: So you were very kind to speak about putting 39:58.967 --> 40:01.197 electrons in the sigma star orbitals. 40:01.200 --> 40:03.170 You don't believe in the sigma* orbitals. 40:05.967 --> 40:07.827 PROFESSOR MCBRIDE: Ellison is not a big 40:07.833 --> 40:09.303 fan of molecular orbitals. 40:09.300 --> 40:09.770 I think. 40:09.767 --> 40:10.727 Is that true? 40:10.733 --> 40:12.403 PROFESSOR ELLISON: Yes. 40:12.400 --> 40:14.470 Yes, that is true. 40:14.467 --> 40:18.467 Look, I do valence bond work. 40:18.467 --> 40:20.897 This is a matter of taste. 40:20.900 --> 40:23.400 There's different ways to view these things. 40:23.400 --> 40:26.530 And in the end, the only thing that 40:26.533 --> 40:27.773 counts is what you measure. 40:32.033 --> 40:34.133 Here, if you have a model that can 40:34.133 --> 40:37.133 account for the patterns that 40:37.133 --> 40:41.603 you've measured, and you can predict what the next values 40:41.600 --> 40:45.470 are going to be, you understand this. 40:45.467 --> 40:47.797 But it's the data is what survives. 40:47.800 --> 40:50.200 The rest of it is all a matter of opinion. 40:50.200 --> 40:52.070 He likes sigma* orbitals, I don't. 40:56.033 --> 40:59.703 PROFESSOR MCBRIDE: You were talking about the stability of 40:59.733 --> 41:04.233 the phenoxy radical, in terms of its resonant stabilization. 41:04.233 --> 41:07.673 So I think these people could help you out with that. 41:07.667 --> 41:09.327 Or at least point out something interesting 41:10.800 --> 41:18.970 Would you say that this radical is stable because you 41:18.967 --> 41:21.727 can draw resonance structures that have 41:21.733 --> 41:21.933 the electrons over here. 41:21.933 --> 41:23.433 PROFESSOR ELLISON: Yes, that's right. 41:23.433 --> 41:24.203 Correct. 41:24.200 --> 41:27.530 PROFESSOR MCBRIDE: But how about if you say that 41:27.533 --> 41:30.503 in the starting 41:30.500 --> 41:32.700 phenol, that's the bond that you're going to 41:32.700 --> 41:34.200 break in here, right? 41:34.200 --> 41:38.000 Here I've got a pair of electrons that I can draw 41:38.000 --> 41:40.770 resonance structures for. 41:40.767 --> 41:41.867 So it looks to me like it's worth more 41:41.867 --> 41:43.927 here than it is here. 41:43.933 --> 41:46.603 PROFESSOR ELLISON: Listen, dream on, big boy. 41:46.600 --> 41:48.700 Look-- 41:48.700 --> 41:52.130 Here, how do I push this thing up? 41:52.133 --> 41:53.403 PROFESSOR MCBRIDE: OK, we'll get that. 42:00.467 --> 42:01.697 PROFESSOR ELLISON: Here. 42:18.367 --> 42:21.767 So this electron is going to get delocalized 42:21.767 --> 42:22.867 over the whole molecule. 42:22.867 --> 42:26.527 If you try to do this with an electron pair, what you're 42:26.533 --> 42:27.803 going to have is-- 42:32.633 --> 42:33.533 OK. 42:33.533 --> 42:46.403 So if I do that, I'm pushing charges around. 42:46.400 --> 42:47.630 Well, I don't like that. 42:50.167 --> 42:53.997 I don't like the fact that the oxygen is going to have-- 42:54.000 --> 42:57.030 you're starting to suck electrons-- 42:57.033 --> 43:01.933 if the electrons migrate down, the oxygen is going to become 43:01.933 --> 43:03.203 positively charged. 43:03.200 --> 43:05.570 So jeez, I just would never do that. 43:05.567 --> 43:06.397 But here. 43:06.400 --> 43:09.930 But what's true is that bond energy, honest to God, really 43:09.933 --> 43:12.033 and truly, is 86 kcal per mole. 43:12.033 --> 43:13.073 That is a fact. 43:13.067 --> 43:22.227 And this is a flippant way to have anticipated this. 43:22.233 --> 43:33.073 Contrast that with, say, methoxy dot-- where's that 43:33.067 --> 43:34.497 electron going to go? 43:34.500 --> 43:36.770 It's really stapled to the oxygen atom. 43:36.767 --> 43:37.927 There's nothing it can do. 43:37.933 --> 43:40.303 It can't go anywhere. 43:40.300 --> 43:51.500 So when you break that bond, you get hydrogen atom. 43:51.500 --> 43:52.300 You get the dot that's just 43:52.300 --> 43:53.900 stuck right there. 43:53.900 --> 43:59.800 As you pull this bond off, the dot now is able to be 43:59.800 --> 44:04.370 delocalized and spread around the whole ring, and this bond 44:04.367 --> 44:11.397 energy, then, in phenol, this bond energy that's going to be 44:11.400 --> 44:13.670 86 kcal per mole-- 44:13.667 --> 44:16.197 this thing lets you measure the absolute heat of formation 44:16.200 --> 44:24.800 298 of this thing. 44:24.800 --> 44:29.630 This low bond energy is going to mean that this heat of 44:29.633 --> 44:32.733 formation is going to be low. 44:32.733 --> 44:36.673 So what that means is, if we're trying to study lignin, 44:36.667 --> 44:38.327 and lignin are trees-- 44:41.400 --> 44:44.430 you take a chainsaw and you're cutting trees down, that's 44:44.433 --> 44:46.833 very tough material. 44:46.833 --> 44:54.103 All these compounds are long, three-dimensional polymers of 44:54.100 --> 44:55.870 aryl alkyl ethers. 44:55.867 --> 44:58.627 So if you know the heat of formation of the phenoxy 44:58.633 --> 45:04.573 radical, this bond turns out to be 62 kcal per mole. 45:04.567 --> 45:12.727 And if you do this in this, it's like 90. 45:12.733 --> 45:15.073 And that's a volt and a half. 45:15.067 --> 45:19.627 So when you heat this, all these molecules break apart, and the 45:19.633 --> 45:22.503 first thing they do is they form phenoxy radicals. 45:22.500 --> 45:26.570 And this triggers the decomposition of these things. 45:26.567 --> 45:32.927 So it turns out, I don't like these things in the neutral 45:32.933 --> 45:34.273 molecule being delocalized. 45:34.267 --> 45:36.197 Because I think you have to separate charge, and 45:36.200 --> 45:39.270 I don't like that. 45:39.267 --> 45:40.697 PROFESSOR MCBRIDE: There are actually people back there who 45:40.733 --> 45:43.233 are smart at this kind of stuff. 45:43.233 --> 45:46.203 Do you guys buy that? 45:46.200 --> 45:47.430 PROFESSOR ELLISON: You? 45:52.567 --> 45:55.067 STUDENT: What I'm thinking is, if you have that kind of 45:55.067 --> 45:59.567 species, you'd think there'd be a spin observable. 45:59.567 --> 46:01.667 PROFESSOR ELLISON: Oh, indeed there is. 46:01.667 --> 46:07.997 If you look at the EPR spectrum of this radical, it 46:08.000 --> 46:09.600 is delocalized all over the place. 46:09.600 --> 46:11.630 And here, you're an expert in this. 46:11.633 --> 46:13.133 You know about all these hyperfine 46:13.133 --> 46:14.033 couplings and whatnot. 46:14.033 --> 46:14.803 PROFESSOR MCBRIDE: Yes, there's coupling 46:14.800 --> 46:15.900 from the protons around here. 46:15.900 --> 46:19.130 It's like NMR. So if the electron spin gets out on 46:19.133 --> 46:22.173 these protons, then it interacts with the nucleus, even 46:22.167 --> 46:24.967 if the molecule's tumbling, you don't have to worry about 46:24.967 --> 46:26.767 the anisotropy. 46:26.767 --> 46:29.397 So it's no doubt it gets delocalized, but why 46:29.400 --> 46:30.130 doesn't this one? 46:30.133 --> 46:35.373 So Barney says it's because he doesn't like to separate 46:35.367 --> 46:37.227 charge in resonance structures. 46:37.233 --> 46:40.633 But that's not-- is this Coulomb's law, or what? 46:40.633 --> 46:42.073 Anybody got an idea back there? 46:47.300 --> 46:48.800 PROFESSOR ELLISON: Well, here. 46:48.800 --> 46:50.830 What do you mean, is this Coulomb's law? 46:50.833 --> 46:52.403 Coulomb's law is what it is. 46:55.267 --> 46:56.497 So here. 46:59.400 --> 47:04.170 If resonance forms like this are important, then that means 47:04.167 --> 47:06.927 that I think, as a consequence of this, you have to have 47:06.933 --> 47:07.603 charge separation. 47:07.600 --> 47:09.970 And I think these are high-energy resonance forms. 47:09.967 --> 47:11.997 And if they're high-energy resonance forms, they don't 47:12.000 --> 47:13.930 contribute to the superposition in the wave 47:13.933 --> 47:16.803 function, is the way I say that. 47:16.800 --> 47:17.230 PROFESSOR MCBRIDE: That's because you 47:17.233 --> 47:18.933 believe in resonance. 47:18.933 --> 47:22.203 G.BARNEY ELLISON: Because I'm a valence-bond guy. But what's 47:22.200 --> 47:26.470 true is this 86 kcal per mole. Nothing can be done about that. 47:26.467 --> 47:27.527 OK. 47:27.533 --> 00:00.003 PROFESSOR MCBRIDE: OK. I think we can thank Professor Ellison.