Hybrid density functional studies on the EPR parameters of heterosubstituted vinyl radicals: substituent effect on the isotropic hyperfine couplings with H-1 and C-13 nuclei

Isotropic hyperfine parameters of a set of vinyl radicals are investigated using the BILYP hybrid density functional. The systems studied are RHbetaCb eta=CalphaHalpha radicals, where R = H, BH2, CH3, NH2, OH and F. Theoretica l results indicate that electronegativity of the substituent strongly affec ts the magnitude of hyperfine coupling with hydrogen nuclei as well as with C-13(beta) A(iso)(C-13(beta)) varies from -8.7 (4.9) to 17.4 G (-17.8 G) l `or Z (E) isomers of the radicals depending on the R group, BH2 and F, resp ectively. In the same order, for Z (E) isomeric forms A(iso)(H-1(beta)) dim inishes from 40.1 (67.7) to 18.4 C (40.9 G) and A(iso)(H-1(alpha)) - from 2 5.6 (24.1) to 1.5 G (1.3 G). The effect of the substituents on the spin and electron density distribution is discussed in the framework of natural pop ulation analysis and theory of atoms in molecules. (C) 2001 Elsevier Scienc e B.V. All rights reserved.