Collect. Czech. Chem. Commun. 1981, 46, 2924-2934

1H NMR spectra of some chloro-alkenes

Seán Cawleya, Jan Schramlb, Petr Svobodab, Robert Ponecb and Václav Chvalovskýb

a Regional Technical College, Kilkenny Road, Carlow, Eire
b Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, 165 02 Prague 6-Suchdol, Czechoslovakia


1H NMR spectra and electric dipole moments of a series of propene derivatives, (CH3)3-nCln.CCH=CH2 (n = 0-3), were measured and the spectra analyzed. Discrepancies in literature data on compounds with n = 0 and 3 are probably due to systematic spectrometer errors. Vinylic proton chemical shifts are found to vary linearly with n in the direction expected on the electronegativity ground (the variations with n occurs in the order HA > HB ≥ HC). Calculations show that even with the extreme reported values of C-C and C-Cl bond magnetic anisotropies, the shift variations with n cannot be accounted for by magnetic anisotropy effects of a freely rotating (CH3)3-nClnC group. Similar calculations rule out electric field effects as the dominant factor. On the other hand, the electron charge distribution, as obtained from CNDO/2 calculations, including d-orbitals and employing Del Bene-Jaffé parametrization, is linearly related to the vinylic proton shifts. This finding supports the earlier interpretation of NMR spectra of vinylsilanes in terms of back-bonding. The vinyl proton-proton coupling constants decrease with increasing n, the changes being larger in the constants which couple proton A (cis) to the other two.