Substituent effects on indirect carbon–carbon couplings,J(CC), in substituted thiophenes,pyrroles, and furans studied by experiment and theory

An excellent linear correlation is found between a large set of experimental spin–spin carbon–carbon coupling constants, J(CC), in thiophene, pyrrole, and furan systems and the corresponding B3PW91/6‐311++G(2d,p)//B3PW91/6‐311++G(2d,p) calculated estimates. The correlation does not differ significantly from the simplest relationship possible, J(CC)_exp. = J(CC)_calcd., within a small and random spread of about 1 Hz. There are 285 experimental values considered, and 202 out of these are new and come from the present work. The character of the correlation indicates that rovibronic effects on aromatic J(CC)'s, and those of nuclear motions on aromatic J(CC)'s are practically negligible. All of this is in a perfect agreement with our recent extensive studies on aromatic J(CC)'s in pyridine and benzene ring systems. As has been shown by computations, not only large one‐bond couplings but also almost all long‐range ones occurring between the carbons of the heteroaromatic rings are, with a few exceptions, positive. Significant substituent effects experimentally observed in the one‐bond as well as long‐range couplings are very accurately reproduced by the computation. The experimental coupling magnitudes vary from ca. 1 to 98 Hz. The J(CC)'s computed for the model variously substituted trimethylsilyl and fluoro derivatives, which are not easily accessible experimentally, span a range of about 130 Hz, from ca. ?2 in up to ca. +125 Hz . Copyright © 2012 John Wiley & Sons, Ltd.