Development and application of new NMR technique

我们提出了一种新的HMBC技术，称为恒定HMBC（CT-1-HMBC），它能够改善F维碳信号的分离，HMBC的问题之一是由于^1H-^1H耦合引起的J调制<13>通过<13>在t周期期间^C信号与其相关质子的耦合导致Fl维^C信号的谱线展宽。这种不期望的效应连同12 C信号的差的分离<13>有时可能导致交叉峰的分析的困难。为了克服这个问题，我们开发了一种新的技术，恒定HMBC（CT-HMBC），我们提出了两种类型的CT-HMBC实验，CT-HMBC-1和CT-HMBC-2。采用恒定时间方法的目的是在2D演化时间（t_1）期间保持homopolymer 1H-1HJ调制的效果恒定。CT-HMBC-1是常规HMBC的类似物，通过引入恒定的时间段而略微修改。由于这一修改，^1H-^1H J调制效应在恒定时间段内保持不变。在CT-HMBC-2脉冲序列中，^1H-^1H和^<13>C-^1H J调制效应都是固定的。在这两种方法中，为了得到满意的结果，必须通过估计来设置适当的恒定时间段（*_3）。恒定周期（*_3）取决于t1维度的数字分辨率。另<2->一方面，CT-HMBC-1光谱的灵敏度可与常规HMBC实验相媲美。因此，强烈推荐CT-HMBC-1实验用于复杂有机化合物的结构研究。

We present a new version of the HMBC technique named constant HMBC (CT-1-HMBC) which enables to improve the separation of carbon signals in the F dimension.One of the problems of HMBC is that J-modulation due to ^1H-^1H coupling causes line broadening of the ^<13>C-signals in the Fl dimension through couplings of the ^<13>C-signals to their relevant protons during t period. This undesirable effect together with poor separation of ^<13>C-signals may sometimes result in the difficulty for analysis of cross peaks. In order to overcome this problem, we have developed a new technique, constant HMBC (CT-HMBC).We propose two types of the CT-HMBC experiments, CT-HMBC-1 and CT-HMBC-2. The purpose of employing the constant time method is to keep the effect of the homonuclear 1H-1H J modulation constant during the 2D evolution time (t _1). The CT-HMBC-1 is an analog of the conventional HMBC slightly modified by introduction of the constant time period. Due to this modification, the effect of ^1H-^1H J-modulation remains unchanged during the constant time period.In the of CT-HMBC-2 pulse sequence, both the effects of ^1H-^1H and ^<13>C-^1H J modulation are fixed. In both methods, the appropriate constant time period (*_3) has to be set by estimation to get satisfactory results. Constant period (*_3) depends on the digital resolution of the t1 dimension. Longer time duration (*_3), will cause the decrease in the sensitivity due to T_<2->.On the other hand, CT-HMBC-1 spectra can be obtained with good sensitivity comparable to those taken by conventional HMBC experiments. Therefore, the CT-HMBC-1 experiment is highly recommended for structural studies of complicated organic compounds.