Heteronuclear Multiple Quantum Correlation is an experiment that identifies protons with their directly bound carbons. The puise sequence utilizes zero and double quantum coherence between J-coupled protons and carbons (hence the name) to label each proton with the frequency of the directly bonded carbon in the F1 dimension of a two dimensional experiment. The conversion of transverse magnetization is mediated by a delay 1/1JCH (i.e. the inverse of the one bond coupling constant) and a carbon 90° pulse. The size of 1JCH is dependent on the carbon hybridisation, being 12O Hz for an sp3 carbon, 16O Hz for an sp2 carbon and 250 Hz for an sp carbon. As a compromise, we choose 1JCH of 14O Hz for this experiment although, if there are no aromatic or alkene fragments in the compound, 1JCH = 120 HZ is a better choice. The experiment is sometimes implemented in its non-decoupled form to measure 1JCH because of the dependency of 1JCH on hybridisation, electronegativity and ring size.

HMQC is the equivalent of HETCOR but, because it is proton-detected, HMQC is more sensitive than HETCOR.

The Problem:

Identify the protons that are directly bonded to each carbon in the complex natural product, Drimentine D. The experiment in combination with DEPT is particulary useful for identifying diastereotopic protons. drimentine D molecule

The Solution:

Each proton-carbon pair has a single crosspeak. 13C nuclei that have diasteriotopic protons have two correlations (some of these crosspeak pairs are boxed in the spectrum below).

drimentine D spectrum

Australian National University NMR Centre home page