Indirect carbon–carbon spin–spin couplings across one, two and three bonds in pyridine and diazine systems: experiment and theory

Abstract

An excellent linear correlation is found between a large body of experimental spin–spin carbon–carbon couplings, J(CC), across one, two and three bonds in pyridine and diazine ring systems and the corresponding B3PW91/6‐311++G(d,p)//B3PW91/6‐311++G(d,p) computations. 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 276 experimental values considered, and 124 out of these are new and come from the present work. The aromatic carbon–carbon couplings vary from −7.6 through +78.5 Hz. It is shown that the correlation provides a reliable tool for predictions of the signs of aromatic J(CC)'s even if the magnitudes of the latter are of the order of 1 Hz. It is demonstrated, for the first time, that the relatively weak 2 J(CC) couplings, in the heteroaromatic systems studied, can bear either sign and span a considerable range of about 11 Hz. 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 analogous benzene ring system. Substituent effects on the aromatic J(CC)'s turn out to be significant not only for 1J(CC)'s but also for most of 3J(CC)'s and 2 J(CC)'s, and the computation neatly reciprocates these trends. Copyright © 2008 John Wiley & Sons, Ltd.

Structural studies on aryl‐substituted enaminoketones and their thio analogues. Part II. Experimental and DFT calculated carbon–carbon coupling constants, nJ(CC)'s (n = 1–3)

“…As a matter of fact our recent results have shown that DFT computations can be considered to be a reliable tool for predicting the signs of the aromatic carbon-carbon couplings, even if the latter are quite weak. [14,15] In view of the good quality of the linear correlation between the experimental and calculated J(CC)s, as is demonstrated in Fig. 2 and Eqn (1), the same seems to be valid in the case of the couplings between the aromatic and aliphatic carbons studied in the present work.…”

“…substituted benzenes [14] and pyridines. [15] A comparison of the data obtained in the present work with those obtained by us for enaminoketones, which bear the aliphatic substituents only and can adopt both the E and Z configuration around the double bond, [13] allowed us to draw some conclusions regarding the influence of the geometry of the compound on this important in structural studies parameter. [16 -20] …”

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

“…The results presently obtained clearly demonstrate that it is possible, at the present level of theory, to reliably reproduce the experimental J (CC)'s. We will show that the relationship between the calculated and experimental J (CC)'s for the five‐membered heterocycles concerned can be reduced, as was already observed by us for benzene and pyridine derivatives, to the simplest relationship possible, that is, J (CC) exp. = J (CC) calcd.…”

“…Our recent experimental and theoretical studies of substituted benzenes and pyridines demonstrated that, at the present level of theory, it is possible to reproduce J (CC)'s in these aromatic structures. The same functionals and basis sets, B3PW91/6‐311++G(d,p)//B3PW91/6‐311++G(d,p), have been consistently used for geometry optimizations and for computations of J (CC)'s; 282 couplings were considered in benzene systems and 276 in substituted pyridines . In both cases, the linear regressions are close to the form of J (CC) exp.…”

“…It is important in the case of 2 J (CC)'s, which can bear either sign; obviously in some compounds, the relevant magnitudes can be close to zero. It was demonstrated that 1 J (CC)'s and 3 J (CC)'s are invariably positive; rough trends were observed between the substituent effects and Pauling's electronegativities of the first atoms of the substituents concerned.…”