The 2D Heteronuclear Chemical-Shift Correlation (HETCOR) experiment has been the more used experiment based on carbon detection to trace out the directly-bonded proton-carbon connectivities.

Easy implementation on any AVANCE spectrometer.

The basic 2D HETCOR pulse sequence can be derived from the 2D FUCOUP experiment by inserting heteronuclear decoupling in both F1 and F2 dimensions. Heteronuclear F2 decoupling can be achieved inserting a refocusing period (D3) after the 90º carbon pulse that permits to gate on the decoupling during carbon acquisition. On the other hand, heteronuclear F1 decoupling can be achieved inserting a 180º carbon pulse midway through the evolution period t1 and adding a defocusing period (D2) after it in order to get the desired antiphase magnetization prior to polarization transfer ( 78JCS684 and 81JMR501-42 ). In addition, broadband proton decoupling can be achieved in the F1 dimension replacing the 180º carbon pulse placed in the middle of the variable period by a BIRD cluster ( 83JMR517-53 ). Phase sensitive versions ( 84JMR170-60 and 92MRC287 ) and modified experiments using the BIRD cluster ( 93JMRA41-101 ), an X-filter to remove ABX strong coupling signals ( 99JMR89-138 ) and semi-selective variants ( 88JMR382-78 ) have also been proposed.

The 2D HETCOR experiment can be recorded in routine/automation modes. The number of experimental parameters to optimize is minimum. Among pulse widths, transmitter frequencies, levels of  digitization and sweep widths in both F1 and F2 dimensions, D2 must be set to 1/2*J(CH) and D3 delay optimized as in 1D refocused INEPT experiment. A good compromise is D3=0.3/J(CH). A relaxation delay of 1 second is generally used.

More details on practical implementation of 2D HETCOR experiments on AVANCE spectrometers can be found in

Tutorials: 2D X-detected experiments

The 2D HETCOR spectra show a typical single cross-peak at the intersection of the chemical shift frequencies of directly-bonded proton-carbon pairs. Such spectra are free of misleading responses and only artifacts due to heteronuclear virtual coupling has been described. These virtual coupling effects can be recognized in a HETCOR experiment with D2=0.

Presently, improved sensitivity ratios are obtained from heteronuclear correlation experiments based on proton detection as, for instance, the HMQC and the HSQC experiments.

Related experiments:

2D X-detected experiments