Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (01): 43-54.

• THEORETICAL AND COMPUTATIONAL CHEMISTRY •

Origin of the cis-Effect: a Density Functional Theory Study of Doubly Substituted Ethylenes

ZHAO Dong-Bo1, RONG Chun-Ying1, JENKINS Samantha1, KIRK Steven R.1, YIN Du-Lin1, LIU Shu-Bin1,2

1. 1 Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China) and Key Laboratory of Resource Fine-Processing and Advanced Materials of Hunan Province, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, P. R. China;
2 Research Computing Center, University of North Carolina, Chapel Hill, North Carolina 27599-3420, U. S. A.
• Received:2012-08-21 Revised:2012-11-12 Published:2012-12-14
• Supported by:

The project was supported by the‘XiaoXiang Scholar’Talents Foundation of Hunan Normal University, China (23040609), Hunan Provincial Innovation Foundation for Postgraduate, China (CX2012B223), and Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province, China. The Hundred Talents Foundation of Hunan Province is gratefully acknowledged for the financial support to S. J. and S. R. K.

Abstract:

It is well known that the trans isomer of a doubly substituted ethylene is more stable than its cis counterpart because of the more favorable electrostatic and steric interactions in the trans conformer. Exceptions do exist nevertheless. 1,2-Difluoroethylene is such an example, so is 1,2-dichloroethylene. The unusual stability of the cis isomer of these doubly substituted ethylene compounds is referred to as the cis-effect, whose nature and origin are still not well understood. In this work, using 12 simple molecules, XHC=CHY (X, Y=F, Cl, Br, CN, CH3, OCH3, C2H6), as examples, we perform systematic studies to investigate the validity, nature, and origin of this effect. Among the systems studied, 9 of them exhibit the existence of the cis-effect and the remaining 3 systems are conventional systems used for the comparison purpose. We employ a large number of density functionals and basis sets to confirm its validity. We also use a few well-established analysis tools, such as natural bond orbital (NBO), energy decomposition analysis (EDA), density functional reactivity theory (DFRT), and non-covalent interaction (NCI) analysis, to pinpoint its nature and origin. We found that there exists a weak but attractive non-covalent interaction between the two substituting groups in the cis conformer. We also found that electrostatic, steric, and kinetic energies all play important roles for the validity of the cis-effect. Nevertheless, none of these quantities can be solely used as the single reason governing the general validity of the cis-effect, suggesting that the origin of the effect is complicated and its validity results from compound interactions from a number of interactions. In this work, we employ two-variable explanations to justify its validity through the electrostatic interaction plus steric effect or kinetic energy, with which reasonable fits with R2=0.86-0.87 were obtained.

MSC2000:

• O641