Studies on the Conjugated Double Bond Systems. VIII. On the Electronic Structures of Furan, Pyrrole and Thiophen

Electronic structures of furan, pyrrole and thiophene were investigated by the use of the molecular orbital method. And values of energy levels, resonance energies, π-electron densities and bond orders were calculated. As the result of these calculations, it was found that nonbonding electrons of hetero-atoms migrate into carbon atoms and the degree of these electron migrations increases in the order of furan, pyrrole and thiophene.