Low-pass Filter HMQC versus HMBC

7 VARIANTS OF THE H- Sn HMQC PULSE SEQUENCE 5.7.1 Low-pass Filter HMQC versus HMBC 

In their initial work Bax and Summers [11] proposed to optimize the HMQC 

In this sequence the first pulse creates multiple-quantum (MQ) coherences from proton antiphase magnetization having evolved under a /( C, H) coupling, while the second C pulse creates such MQ coherences for the magnetization arising from couplings. Adequate phase cycling 

In special cases this low-pass / filter approach may be useful for organotin applications as well, for instance to suppress selected crosspeaks. However, it should be noted that the same result can be obtained for H- Sn correlations by carefully choosing the 1/(2/) delay, as discussed above (see Section 5.5). 

A short remark about the relevance of HMQC and HMBC experiments and nomenclatures should be done here. Initially, Bax et al. [9] introduced the HMQC technique for specific editing of H- C pairs correlated by direct V( C, H) couplings. The HMBC technique was proposed subsequently by Bax and Summers [11] to edit specifically multiple bond correlations through /( C, H) couplings (n = 2 and 3), which explains the HMBC acronym. From the point of view of the pulse sequence the introduction of the low-pass filter, which consists of a supplementary 90° pulse and an extended phase cycle, is 

---