CONFORMATIONS, STABILITIES, AND CHARGE-DISTRIBUTIONS IN 2-MONOSUBSTITUTED AND 3-MONOSUBSTITUTED THIOPHENES - ABINITIO MOLECULAR-ORBITAL STUDY

Ab initio molecular orbital theory with the STO-3G basis set is used to determine the equilibrium geometry for thiophene and to study the conformations, stabilities, and charge distributions of several monosubstituted thiophenes. The conformational preferences are rationalized in terms of orbital interactions and electrostatic interactions. The stabilizing effect of substituents attached to thiophene, furan, and benzene rings is compared. As with the furyl group, the thienyl group usually prefers to act relative to phenyl as a πelectron donor and σelectron acceptor and it is stabilized by substituents characterized as being πelectron acceptors andσelectron donors. These effects are greater at the 2 than at the 3 position. Differences between the thiophene and furan derivatives are discussed. © 1979, American Chemical Society. All rights reserved.