16.11 : 二维核磁共振（2D NMR）：异核相关技术概述

Heteronuclear correlation techniques investigate the coupling between different nuclei—often a proton and carbon-13 or nitrogen-15.

A typical spectrum displays the X-nucleus chemical shift on one axis and the proton chemical shift on the other, with cross-peaks indicating the proton–X correlations.

Standard heteronuclear correlation spectroscopy, or HETCOR, enhances X-nucleus signals using polarization and is preferred for high X-axis resolution.

The heteronuclear single-quantum and multiple-quantum correlation techniques—HSQC and HMQC —explore proton–X one-bond correlations.

HSQC generates a spectrum like that of HMQC but uses a different suppression method, resulting in higher X-nucleus peak resolution.

Heteronuclear multiple-bond correlation or HMBC, focuses on longer-range proton–X connectivity, ignoring direct one-bond correlations.

Gradient HMBC enhances the suppression of interfering signals, making it useful for complex molecules with overlapping signals