Name: ケム 203有機分光学講義02.C,H,Oを含む官能基 (Chem 203. Organic Spectroscopy. Lecture 02. C,H,O-Containing Functional Groups)
Uploaded: 2021-01-14T05:21:10.000Z
Duration: 51 min 47 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

A couple of people are filing in, I’ll get started.

程度の副詞

So last time I tried to give an overview of the course and also an overview to IR spectroscopy.

And I guess one of the take home messages I was trying to give was that IR spectroscopy

really should be something that you [inaudible]

And you want to make it easy to do the experiments and I suggested techniques like placing a

drop on a thin film or [inaudible] form a solution in forming a calcium fluoride cell;

There are things—and I hope the example that I started class with really brings it

home—there are things that IR just excels at that, I’ll add, NMR doesn’t excel at.

NMR is going to talk  to you about some things; if you’ve got an aromatic ring or an alkene in your molecule

with a hydrogen on it and it’ll probably talk to you pretty well.

But if you have an unusual ring size like we saw in the beta lactone or a 5 membered

ring with a carbonyl—IR can talk to you in a way that NMR just can’t talk to you,

that mass spec isn’t going to talk to you, that UV, which we’re not going to cover

in this course, isn’t going to talk to you.

Other things like a terminal alkyne—we’ll have a problem later on, I guarantee, everyone

is going to look at this and say oh wow, afterward, you know, only with NMR data and not realize,

and then something really talks—there are probably about 2 dozen pieces of information

that easily IR can talk to you and this is what I’m going to put in.

So today I want to talk about CH containing functional groups; in other words I want us

to be able to know how to identify alkane groups and alkene groups, or fragments within

molecules, arene, in other words aromatic, alkyne.

And one of the pieces of philosophy that I’m going to try to take particularly as we get

to certain functional groups is to start to look for patterns here.

Because it’s not so much about tabulating peaks—it’s really about being able to

I want to talk today about oxygen containing functional groups, and we’ll go through:

alcohols, aldehydes, ketones, esters, acids—carboxylic acids of course—acid chlorides, and let’s

obviously there are other functional groups and I’m just picking ones that I think are

Some of the features I hope we get a chance to talk about today, if not today tomorrow,

more about ring size which I think is really cool in the case of cyclic ketones and esters,

conjugation and understanding the principles involved, inductive effects, and—probably

not this time, as a matter of fact, certainly not this time—we’ll talk about nitrogen

we’ll talk about amides, amines, ammonium salts, maybe nitriles—nitriles are another

one that IR I think really shines for identifying—and maybe nitro compounds.

So one of the things I’m going to urge you to do when you look at an IR spectra is really

So let me give you my take because part of reading is not just sitting and tabulating

every peak, it’s knowing what’s important.

So when I look at an IR spectrum, generally in my mind’s eye I think from about 4000

to about 600 and probably—and of course these are centimeters^(-1) , wavenumbers,

[inaudible] waves per centimeter—and probably also in my mind’s eye I end up drawing a

And I think this really ends up dividing the spectrum into some important regions. So if

you have an IR spectrum maybe you see something like this. You’re reading in—I’m going

to label my axis, of course you’re going to have %T, and of course your spectrum is

So you see some peaks, and some stuff over here. Now, the region over here from 1600

to about 3600 is the functional group region. And that’s generally what I look at.

There’s information to be had in this region from 1400 to about 600 wavenumbers; that’s

If we have a chance maybe on Wednesday we’ll take a look at how you can find aromatic substitution

patterns from here; I think in one of the homework problems there’s a—the textbook,

by the way, take the time to flip through it. It’s got very nice appendices that are

One of the appendices, for example, will give you some correlating peaks to be able to figure

out whether an alkene is—what the substitution pattern is on an alkene; whether it’s terminal,

whether it’s cis, or whether it’s trans.

Anyway—so generally my eye will sort of be drawn to this region; above 1600 I’ll

look for carbonyls, I’ll generally look about this region, just above 2000, because

normally you don’t expect anything there.

If I see anything there it’s going to send up a red flag that there may be something

interesting; we already talked about alkynes.

Generally I won’t pay too much attention to this region right below 3000. But there

are a few things that can show up here at about 2820 and 2720 can be indicative of an

aldehyde if you have the right sort of carbonyl peak.

Things down from 3000 of course might clue you in to alkenes and aromatics. And then

over here, and particularly over here, you get clued in to carboxylic acids.

So it’s really this issue of being able to read the spectrum that I think is really

so key in being able to get some useful information out of IR.

One of the things—it’s not just the position of peaks that counts it’s their relative

intensities, and that can clue you in a lot.

So, for example carbonyl and alkenes, C double bond C, both show up in the same region but

they have different appearances to them. So for example, a carbonyl C=O is generally strong,

and that’s going to mean usually strong relative to other peaks, but again part of

that is what fraction of the molecule is the carbonyl occupying.

If you have a ketone with 6 carbons in it, you’ve got a lot more carbonyl groups in

that path length than if you had a ketone with 60 carbons. So your ketone peak, your

carbonyl peak, is going to be stronger in smaller molecules than in bigger molecules.

Carbon-oxygen single bonds, anything with a big dipole moment in general—not always,

but in general—has strong peaks. So anything where you have substantial differences in

Bonds that are often weak or moderate are compounds like alkynes, carbon-carbon triple

bond stretches, alkenes, carbon-carbon double bond stretches of various sorts, say, terminal

alkenes and internal alkenes—and we already talked about if there’s no change in dipole

moments, so if you have, say, an alkyne with two alkyl groups on the end, you’re probably

not going to see-or most certainly won’t see—the carbon-carbon triple bond stretch.

If you have an alkene that’s tetra-substituted you’re probably not going to see the carbon-carbon

double bond. So let’s say usually not seen—internal alkenes, internal alkynes.

We talked a little bit when I was talking about methylene groups and I talked about

the asymmetric stretch and symmetric stretch, we talked a little bit about CH groups.

CH stretches are generally very sharp; so things that might clue you in—as I said,

alkyl generally not that informative, but usually they fall between about 3000 and about

2840 wavenumbers. And if you’re good, you really should be able to draw a line at about

2840 in the spectrum because, as I was saying, aldehydes can have little CH stretches and

Alkenes, arenes—aromatics if you prefer—generally we’re talking about 3100 to about 3000.