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2D Constant-Time HETCOR
DESCRIPTION
The 2D constant-time heteronuclear correlation (CT-HETCOR) experiment uses a constant-duration evolution period to eliminate all homonuclear couplings, including geminal couplings, from any cross-peak in the 2D HETCOR map.

REQUIREMENTS
Easy implementation on any AVANCE spectrometer.
VERSIONS
In the basic CT-HETCOR pulse sequence ( 85JMR304-64 ), simultaneous 180º proton and carbon pulses are systematically repositioned through the evolution period, the location changed in each successive experiment. Homonuclear spin couplings are insensitive to this refocusing pulses and further, since the duration of the evolution period is fixed, they do not modulate during t1. An analogous modification of the DEPT correlation experiment has also been proposed ( 87MRC579 ). Alternatively, combinations of the CT approach with the BIRD cluster ( 88MRC358 , 88MRC1068 , 88MRC881 , and 92MRC287 ) resolve the problems of limited F1 resolution and strong intensity dependence. Limitations and artifacts of these alternatives have also been studied ( 86JMR524-63 , 86JMR100-69 , 88MRC1068 , 90JMR135-88 , 90MRC496 , and 91MRC316 ).
EXPERIMENTAL DETAILS
The 2D CT-HETCOR experiment can be recorded in routine/automation modes.
Acqusition parameter set-up as described in 2D HETCOR experiment. However, the most important parameter in CT experiments is the constant-time period length. A value of 12 or 20 ms is recommended in which case the number of increments of the evolution time should be 24 or 16, respectively (T=t1(max)/2). Thus, digital resolution in F1 dimension will be quite coarse and the limit of resolution will be limited to 1/t1 (c.a. 50 Hz). That means peaks closer will not be resolved by this experiment. The most widely used version of this experiment is the COLOC experiment that permits to trace out long-range proton-carbon connectivities.

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

  • Tutorials: 2D X-detected experiments
    • SPECTRA
    A typical 2D heteronuclear correlation map is obtained in which complete proton decoupling in F1 is achieved.
    RELATED TOPICS
    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