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1 2003

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Influence of Substituents on Carbon-carbon Coupling Constants in Substituted Acetylenes

Biedrzycka Z., Kamieńska-Trela K.

Polish Journal of Chemistry

2003

Vol. 77 / nr 11

1637-1648

Indirect spin-spin carbon-carbon coupling constants across a triple bond have been calculated using the DFT method in a large series of substituted acetylenes and compared with those determined experimentally. The DFTcalculated coupling data not only follow the trends observed for the experimental results but also the absolute 1JCC values are very well reproduced (in most cases within several Hz). It has been found that the magnitude of the coupling is strongly dependent on the electronegativity of the first atom of the substituent attached to the triple bond which is described by the equation: 1JXCCY (TOTAL) = 25.9 EXEY + 5.4. The smallest 1JCC coupling calculated for Li2C2 is 31.6 Hz and the largest one for C2F2 420.9 Hz, which reflects the dramatic changes occurring in the electronic structure of the triple bond upon substitution. A rough linear correlation has been found between the ln 1JCC(DFT) and the DFT optimized bond lengths, rCC. Additionally, the couplings across one Csp3-Csp and Csp2(arom)-Csp single bonds and those across two Csp3-CC and Csp2(arom)CC bonds have been derived and discussed.