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

Abstract

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. À2 in up to ca. +125 Hz .

Dimericbiscognienyne A: A Meroterpenoid Dimer from Biscogniauxia sp. with New Skeleton and Its Activity

“…To determine the relative configuration of 3 , the key 1 H– 1 H coupling constants of the above four relative configurations were calculated by quantum chemical methods at three levels of B3LYP/6-311+g (2d, p), APFD/6-311++g (2d, p), and B3PW91/6-311++g (2d, p) (Supporting Information). All of the calculated results showed that the calculated 1 H– 1 H coupling constants of (1 R , 2 R, 3 S , 4 R )- 3 were similar to the experimental one (Figure ). Therefore, the relative configuration of 3 was assigned as 1 R *, 2 R *, 3 S *, 4 R *.…”

Evaluating the accuracy of theoretical one‐bond 13C─13C scalar couplings and their ability to predict structure in a natural product

“…[13,17,51] Theoretical methods from calculating 1 J CC values have also been developed using various approaches. [2,11,18,24,28,[52][53][54][55][56][57][58] Recent theoretical work often relies upon the secondorder polarization propagator approximation technique [8,11,12,20,22,24,30,31,39,56,59] or density functional theory (DFT) computations [13,14,17,19,23,[26][27][28]33,[36][37][38]41,43,45,54,55,57,60] that employ the EPR-III [61,62] basis set. [3,26,28,30,…”

“…Stereochemical configuration also influences 1 J CC coupling, where, for example, the 1 J CC coupling in methyl α‐D‐mannopyranoside differs from the β‐D‐mannopyranoside by 4 Hz . Another important contributor to 1 J CC couplings is the presence of adjacent heteroatoms where the heteroatom electronegativity and lone electron pair orientation have been correlated with the magnitude to the 1 J CC coupling. Ring conformation, ring strain, and percent s‐character in a given C─C bond have also been experimentally and theoretically shown to influence 1 J CC couplings.…”

“…Synthetically 13 C‐enriched products were frequently employed in these studies to enhance the signal‐to‐noise ratio. Presently, several 1 J CC values can be measured in a single experiment at natural abundance with the carbon‐detected 2D INADEQUATE experiment or the proton‐detected Adequate Double Quantum Transfer Experiment . Theoretical methods from calculating 1 J CC values have also been developed using various approaches .…”

“…Theoretical methods from calculating 1 J CC values have also been developed using various approaches . Recent theoretical work often relies upon the second‐order polarization propagator approximation technique or density functional theory (DFT) computations that employ the EPR‐III basis set . The EPR‐III basis, although originally developed to predict hyperfine coupling constants in electron paramagnetic resonance, has also been found to accurately reproduce 1 J CC couplings .…”