Revisiting the ‘cis-effect’ in 1,2-difluoro derivatives of ethylene and diazene using ab initio multireference methods

Abstract

The relative stabilities of cis- and trans- isomers of 1,2-difluoroethylene and 1,2-difluorodiazene have been studied via the state-specific multireference coupled cluster (SS-MRCC) method and its perturbative counterpart through the computation of the optimised structures and corresponding energies. Despite the existence of several cis-destabilising mechanisms, present calculations reveal the energetic preference of the cis- isomer (the cis-effect) for the systems considered here. Differences in structural parameters and vibrational frequencies among cis- and trans- isomers have been discussed. Very good agreement of our estimates has been found with the benchmark theoretical and experimental results. The SS-MRCC methods produce a smooth and consistent behaviour across the entire torsional surface for the cis–trans isomerisation indicating that the method has sufficient flexibility to model large changes in electronic structure that accompany chemical changes.

Keywords:

• 1,2-difluoroethylene
• 1,2-difluorodiazene
• coupled cluster calculations
• optimised structures and energies
• cis–trans energy differences
• vibrational frequencies

Acknowledgements

A. Ghosh acknowledges the BSR fellowship of the UGC (India). S. Chattopadhyay acknowledges the infrastructural facility developed in his department through UGC-SAP programme.

Additional information

Funding

This work has been funded by the Department of Science and Technology, India [grant number SR/S1/PC-61/2009].