A Molecular Orbital Study Comparing the Effects of Heteroatom Substitution in trans-1,3-Butadiene, AII-trans-1,3,5-Hexatriene, and Benzene

To gain more understanding of the nature of the perturbation that results from heteroatom substitution in conjugated polyenes and in an aromatic ring environment, we have carried out calculations on trans-H2C=X(H)-CH=CH2, atl-trans-H2C=CH- [GRAPHICS] N, Si, and P, using the 6-31G*(5D] basis set with full geometry optimization. Linear relationships are found between (a) the C-X and C-C bond lengths, (b) the total overlap population in the C-C, C-N, C-Si, and C-P bonds and the bond length, and ( c) the total atomic charge on the N, Si, and P atoms and the corresponding C atom in the various structures, and the electronegativity of N, Si, P and C. Whereas Si is more strongly bonded in the diene and triene compared to the aromatic ring, P, like N, appears to be bonded equally well in all three structural environments.