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Logic Puzzle #46: Negative correlation on the HSQC-DEPT … Solution

February 14, 2014

An HSQC-DEPT experiment shows one-bond correlations. The CH and CH3 groups are generally phased positive (red) and the CH2 groups are phased negative (blue).

For the following known compound, the 1H -13C HSQC-DEPT spectrum (collected at 150 Hz coupling constant) below shows a negative correlation (blue) at 2.72 and 61.1 ppm with a 1H integral of 1.0. The correlation is attributed to the terminal alkyne CH group. One expects the correlation to have a positive phase and thus appear red in colour. Herein, the spectrum shows a correlation of the opposite phase as a result of the high C-H coupling (~250 Hz). In some cases, the C-H coupling from alkyne group can be weak or missing.

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