October 21, 2008
The 1H-13C HMQC, HSQC, DEPT-HSQC, HSQC-TOCSY and HETCOR experiments offer the elucidator information on the proton-carbon connectivity. The interpretation process comes down to 3 basic assignments: the correlation belongs to a methyl, methylene or methine carbon. A methyl or methine carbon exhibits at most a single correlation between the 1H and 13C axes. A methylene group can exhibit 1 or 2 correlations depending on whether the protons are anisochronous.
Three regions of a 1H -13C HSQC spectrum for quinine are shown below.
A single 1H-13C correlation is observed for a CH and CH3.
For anisochronous methylene protons, 2 correlations are observed.