应用相敏HMQC和HSQC谱准确测定异核碳-氢偶合常数

准确测定各种同核和异核偶合常数是核磁共振（NMR）方法研究的一个非常跃的领域。首先，各种三键偶合常数通过Karplus关系式^1]反映了相应二面角的大小，因此，多键偶合常数的准确测定直接影响分子结构确定的精确性。其次，由于稀液晶溶剂体系NMR方法的发展^2]，准确测定各种异核键偶合常数也显得非常重要，特别是应用场相关偶合常数研究分子在磁场中的取向时，对异核－键偶合常数测定的准确性要求更加严格^3]。异核－键偶合常数的最准确的测定方法是异核偶合调制的HSQC（Heteronuclear Single-Quantum Coherence)实验^3]，它通过测定一系列异核耦合调制的二维HSQC谱，对交叉峰的强度进行分析来精确确定相应的异核－键偶合常数。这一方法的缺点是比较费时。作者在异核多键偶合常数的准确测定方面也做了一些有意义的工作^4-6 α]。在前文^5]工作的基础上，本文提出了二维相敏HMQC（Heteronuclear Multiple-Quantum Coherence)和HSQC（Heteronuclear Single-Quantum Coherence)实验，用于准确测定异核－键偶合常数。

Accurate Measurements of Heteronuclear 13C-1H Coupling Constants by Phase-sensitive HMQC and HSQC Spectra

Phase-sensitive HMQC(Heteronuclear Multiple-Quantum Coherence) and HSQC(Heteronuclear Single-Quantum Coherence) experiments with t1-noise reduction are proposed for the accurate measurement of heteronuclear one-bond 13C-1H coupling constants. The resulting 2D spectra give anti-phase splittings of heteronuclear one-bond couplings along ω2-dimension, so that the precision of coupling constant measurement is less subject to the residual t1-noise. By combining use of data-fitting procedure on a spectrum with enough digital resolution and signal-to-noise ratio, a precision of about 0.03 Hz can be achieved in the measurement of heteronuclear one-bond coupling constants. The proposed method can be very useful for the study of residual dipolar couplings caused by the alignment in high magnetic field and the dynamic frequency shift caused by the cross-correlation between chemical shift and spin dipolar interactions.