October 25, 2013
An HMBC experiment correlates atoms over a longer range from 2-4 bonds. However, it can also exhibit correlations for 1-bond separation.
For a pure, unknown compound, the 1H -13C HMBC spectrum below shows three correlations to the carbon at 42 ppm. The correlations at 3.50 and 4.05 ppm correlate the 1H signal at 3.75 ppm as 1-bond separation for a CH group. The 1H signal at 3.46 ppm correlates as a long range 2-4 bond separation.