Elimination of one bond modulations and direct responses in long range heteronuclear 2D-NMR chemical shift correlation spectroscopy

Date

1987

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Abstract

Modulation of protonated carbon response intensity in long range heteronuclear 2D-NMR chemical shift correlation spectra is discussed. Expressions describing the one bond modulation of response intensity of the C3 methylene resonance of 6,7-dimethoxy-3,4- dihydroisoquinoline and the decoupling of this modulation afforded by a BIRD pulse located midway through the A2 refocusing delay are presented with experimental confirmation. Modified long range heteronuclear chemical shift correlation pulse sequences which incorporate low pass J filters and a combination of low pass J filters and BIRD pulses are also described. In addition to eliminating one bond respones, a one step low pass J-filter is shown to partially decouple one bond modulations when incorporated in the normal long range heteronuclear chemical shift correlation pulse sequence. One and three step low pass J-filters, when utilized in combination with a BIRD pulse located midway through the refocusing delay A21 eliminate responses due to directly attached protons over a range of one bond coupling constants. The inclusion of the J-filter does not adversely affect the ability of the BIRD pulse to decouple one bond modulations. Three step J-filters were observed to produce unacceptable numbers of artifacts.

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Keywords

Nuclear magnetic resonance spectroscopy

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