Theoretical Studies of Geometries of Hexafluoro-1,3-butadiene,Tetrafluoro-l,3-butadiene,and Difluoro-l,3-butadiene Compounds

摘要

The geometrical structures of various isomers of hexafluoro-1,3-bmtadiene(HFBD),tetrafluoro-l,3-bmtadiene(TFBD),and difluoro-1,3-butadiene(DFBD)have been studied theoretically.Natural steric and natural resonance theory(NRT)analyses indicate that the lower energy of skew s-cis conformer of hexafluoro-1,3-butadiene than that of the s-trans conformer is originated from the strong steric repulsions between fluorine atoms particularly in the s-trans conformer.The resonance structures generated by NRT also show that the lone electron pairs of fluorine atoms effectively extend the conjugation,and the large differences in energy among the structural isomers of tetrafluoro-1,3-butadiene and difluoro-1,3-butadiene are in part attributed to the differences in the delocalization energies,in addition to the steric repulsion between fluorine atoms.Other interatomic interactions,such as hydrogen bonding,also play important roles in determination of the structures of isomers of tetrafluoro-1,3-butadiene and difluoro-1,3-butadiene.