about 2-D NMR spectroscopy and what we're going

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

very useful for structure solving.

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

and dynamic effects in NMR spectroscopy,

but we're going to start.

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

like to get you familiar with the tools.

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.

The observe is your FID.

Have you now seen your FID on the spectrometers?

Have you seen the little wiggly, squiggly cosine wave

with a die off [phonetic].

So this is your FID and, of course,

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

over here you have time.

This is literally your signal dying off with time

and the cosine wave that corresponds to the periodicity

of the various nuclei.

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 it has frequency in the units of PPM

on the horizontal dimension

and the reason we call this 1 dimensional NMR spectroscopy is

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

you'd say this is a 2-D graph.

It's because you have 1 time dimension

and that gets transformed to a frequency dimension.

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

in the FID and they get transformed

into 2 frequency domains.

So I'm going to give you just

as I have given you my simplified version

of an NMR spectrometer, an IR spectrophotometer

and a mass spectrometer and so forth.

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

and the second weight becomes t2.

Now these are not to be confused

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.

Now what does this mean?

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

in t2, you're collecting a signal

and it's dying off with time.

So you understand that basic transform

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 2 cycles per second

and others you get a spectrum consisting of many lines.

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

with hypothetically a millisecond

in the first experiment,

then the next experiment 2 milliseconds,

the next experiment 3 milliseconds, the next 4.

Another periodicity occurs.

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

of 2 frequency domains.

It is, of course, plotted 2 dimensionally

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

graph if you will and typically these days the way we express it

is as a topological map so you'll typically see a series

of contours that's just like if you've ever seen a topographical

map of the mountains each contour represents a

certain height.

So a very tall peak has many contours

and a short peak has fewer contours.

So it's 3 dimensions being represented being projected

in two, but again the reason we call this 2-D NMR is not

because there are 2 dimensions in the graph but rather

because there are 2 time dimensions.

All right that's what I want to say about sort

of the basic mechanics of the experiment.

There are 2 general types of 2-D NMR experiments.

One of these experiments is one of these families the one

that we'll be talking mostly about,

is correlation experiments.

Correlation means connectivity.

It means literally what's connected to what.

Another way of thinking of this is coupling.

It can be proton-proton coupling,

it can be proton-carbon coupling,

that's what correlation experiments give you

information on.

You've already been using this type of information

from coupling patterns and coupling constants.

When you see a triplet here, you say, oh, that's a methyl group

and then it integrates the 3 hydrogens you say, oh,

that's a methyl group that's next to a CH2 group.

When you see a quartet here and it integrates to 2 hydrogens,

you say, oh, that's a methyl group that's next

to 3 hydrogens.

Maybe it's next to a methyl group and correlations give

that same type of information.

When you see a 17 hertz coupling in a trans alkene, you say, oh,

that 17 hertz coupling must have a partner somewhere.

Ah, here is its partner that also has a 17 hertz coupling.

So you're already using connectivity information

in helping to deduce your structures.

Two-D experiments provide that information

in a more general term.

The other type of 2-D experiment that we'll be talking

about are Overhauser effect experiments.

We'll be talking more about the Nuclear Overhauser Effect

in a couple of lectures.

Those give rise to information on spatial proximity.

[ Writing on board ]

These can be very useful for information

about stereochemistry and conformation.

All right my philosophy on teaching 2-D NMR spectroscopy

as I said before there's a whole alphabet soup

of techniques out there.

My philosophy is not to bombard us but to give us a small box,

a small tool box of what I'll call core techniques.

In other words, techniques that if we are good at we can use

to solve a variety of problems and then if you're good

with those techniques you'll be able to say oh here's a whole

in my tools where I have a very specialized problem

that isn't being solved by these tools and you can go

to Phil [phonetic] or go to the NMR manual and say, oh,

I'm encountering this particular problem with a COSY

and A Toxi [phonetic] isn't helping me out

but I remember him saying something

that there was some type of technique called a relay COSY

and saying I can add that to my toolbox.

So, okay, the first 2 tools that we'll be talking about are COSY,

which was really the first main 2-D technique.

It stands for correlation spectroscopy.

So this is typically proton-proton

or let's just say homo-nuclear coupling

and then the second technique that we're going to add

to the toolbox is HMQC and this is heteronuclear correlation.