Question

What is the diference between the most common two-dimensional NMR techniques: COSY and HETCOR?

Answer 1

In COSY, the proton spectra are plotted along each axis, while in HETCOR the proton spectrum is on one axis and the `""^13"C"` spectrum is on the other axis.

Explanation:

COSY —`"CO"`rrelation `"S"`pectroscop`"Y"`
(you may also see it written as H,H-COSY)

In COSY, both axes correspond to `""^1"H"` NMR spectra.

The off-diagonal peaks show which protons are coupled to each other.

The COSY spectrum of ethyl but-2-enoate

(from www.chem.ucalgary.ca)

is

(from www.chem.ucalgary.ca)

For example, peak A indicates a coupling between the `"H"` at 6.9 ppm and the `"H"` at 1.8 ppm.

This shows that the `"CH"_3` group is coupled to the adjacent `"H"` on the alkene.

HETCOR — `"HET"`eronuclear `"COR"`relation Spectroscopy

in HETCOR spectra, a proton NMR spectrum is plotted on one axis and the `""^13"C"` NMR spectrum is plotted on the other.

The peaks show which `"H"` is attached to each `"C"`.

Here is the HETCOR spectrum of ethyl but-2-enoate.

(from www.chem.ucalgary.ca)

For example, Peak A indicates that the `"H"` at 4.1 ppm is attached to the `"C"` at 60 ppm.

This corresponds to the `"-OCH"_2"-"` group of the ester.