SQ-SQ experiment for determination of relative signs of small nJ(29Si,13C) couplings in a wide variety of silicon compounds

A modification of double quantum-zero quantum (DQ-ZQ) experiment termed single-quantum-single-quantum (SQ-SQ) experiment is proposed for the determination of relative signs and magnitudes of coupling constants. The modification replaces the multiple-quantum evolution period by two synchronously incremented single-quantum periods. Similarly to DQ-ZQ experiment, the sequence requires only two coupling constants that share one nucleus, the one to be measured and a reference one. This allows application to a larger variety of molecular fragments than traditional 2D sequences producing E.COSY or TROSY pattern. The SQ-SQ experiment eliminates the effects of some other couplings during t(1), thereby simplifying the 2D pattern and increasing the signal intensity in comparison with DQ-ZQ experiment. The presented sequence is particularly designed for the determination of silicon-carbon coupling constants across several bonds at natural abundance using silicon- hydrogen couplings as the sign reference. The signs of silicon-carbon couplings across two and three bonds in dimethyl(phenoxy)silane which cannot be detected by traditional methods and which have not yet been determined are established by the SQ-SQ method here: (2)J(Si,C) = +2.2 Hz and (3)J(Si,C) = -1.7 Hz. Copyright (C) 2009 John Wiley & Sons, Ltd.