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Interpreting an HSQC or HMQC or HETCOR experiment

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.

Hsqc_hmqc_hetcor_str_oct212008

A single 1H-13C correlation is observed for a CH and CH3.

Hsqc_hmqc_hetcor_ch_oct212008

Hsqc_hmqc_hetcor_ch3_oct212008

For anisochronous methylene protons, 2 correlations are observed.

Hsqc_hmqc_hetcor_ch2_oct212008