Name: 化學203.有機光譜學。第17講。二維NMR光譜學介紹 (Chem 203. Organic Spectroscopy. Lecture 17. Introduction to 2D NMR Spectroscopy)
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about 2-D NMR spectroscopy and what we're going

未來進行式

to do we'll be using this as a tool very,

There's a whole sort of alphabet soup of different techniques

but rather than just unleashing a torrent,

I mean people do research in this area just

like they do research in organic chemistry

and so big thing is invent a new technique

to solve specialized problems, but rather than trying to sort

of talk broadly about everything we're going to focus

on getting a few tools in our toolbox and see how

to use these techniques to address different problems.

We'll start out with 2 tools in the toolbox that will be HMQC

and COSY techniques and then we'll add some more tools

and I'll try to put them into some sort of context.

There are 2 additional lectures that aren't specifically on 2-D

that will come in either possibly next time or the time

after that so we'll be talking specifically

about the Nuclear Overhauser effective, which applies

to 1-D NMR as well and we'll be talking about dynamic NMR

Our next homework set will start to bring in 2-D and I'd

All right theory I'm going to start really simple minded

and I think this is actually a good way to think about things.

So, in 1-D, we said the basic idea was your pulse

and then you observe, that's your 90-degree pulse.

Have you now seen your FID on the spectrometers?

Have you seen the little wiggly, squiggly cosine wave

what you've got here is an amplitude domain and then

This is literally your signal dying off with time

and the cosine wave that corresponds to the periodicity

So the whole idea in 1-D Fourier transform is this time domain

on the X axis ends up getting transformed

to a frequency domain and that's your parts per million

and so your spectrum still has amplitude on the vertical axis

and the reason we call this 1 dimensional NMR spectroscopy is

not because this is a 1-D graph, it's not,

and that gets transformed to a frequency dimension.

Now, in 2-D NMR, you get 2 time domains, 2 time dimensions

as I have given you my simplified version

of an NMR spectrometer, an IR spectrophotometer

I'll give you my simplified version of a 2-D pulse sequence.

A 2-D pulsate sequence is going to be pulse weight pulse observe

and so what you do when you do this is you get 2 time

dimensions because the weight is you're waiting for some time,

you're going to vary the weight and then you observe.

So this first weight becomes time 1 and we'll call that t1

with the capital Ts we talked about for relaxation.

Remember we talked about Capital T1 is vertical is spin

relaxation where the magnetization returns

to the Z axis and Capital T2 is spin lattice relaxation

where the magnetization spreads out in the X, Y plane.

These are lower case ts and they in turn transform

when you do a 2-D ft they transform to 2 frequency domains

and so you get a spectrum that might look like this

where you have 1 domain here and this is called your f2 domain

and then another domain here and that's called your f1 domain.

As you're varying, well, you understand here, of course,

that if the periodicity of this signal is 1 cycle per second,

we get a line at 1 hertz and if the periodicity

of this line is 2 cycles per second, you get a line

at 2 hertz and if it's a composite of 1 cycle per second

and others you get a spectrum consisting of many lines.

Now similarly as you vary this t1 let's say starting

the next experiment 3 milliseconds, the next 4.

In other words, your FID what you observe

in this time also shows variation that occurs in time.

Variation, amplitude, a periodic variation.

Those variations transform to the second frequency domain

and so you get a spectrum now that consists

It is, of course, plotted 2 dimensionally

but it is really just as this is actually a 2-D graph this is 3-D

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化學203.有機光譜學。第17講。二維NMR光譜學介紹 (Chem 203. Organic Spectroscopy. Lecture 17. Introduction to 2D NMR Spectroscopy)

couple

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