Structures, vibrational spectra, and relative energetics of FC(O)ONO and FC(O)NO₂ isomers at DFT and ab initio levels

Abstract

The structural and vibrational parameters of FC(O)ONO and FC(O)NO₂ isomers were examined theoretically using the B3LYP/6-311+G(3df) and CCSD(T)/6-311G(d) methods. Four conformers of FC(O)ONO isomer and one FC(O)NO₂ isomer are found here. Among them, the trans–cis and cis–cis FC(O)ONO configuration are new conformers. The energetics were refined with G3//B3LYP and CBS-QB3 calculations. The trans–trans conformer of the FC(O)ONO isomer is found to be the lowest energy structure, with an estimated heat of formation of −104.9 kcal mol⁻¹ at 0 K as determined from CBS-QB3 theory. The next lowest structure is the cis–trans FC(O)ONO lying 1.7 kcal mol⁻¹ above the trans–trans structural form. The highest energy structure is the FC(O)NO₂ isomer with a predicted heat of formation of −84.8 kcal mol⁻¹. A comparison of the relative stability of the FCNO₃ isomers with the isomers of ClCNO₃ shows that the Cl analogues follow the same pattern of stability, as do the F isomers. However, the chlorine isomers are unstable relative to their fluorine analogues.

Keywords:

• density functional theory
• ab initio composite methods
• heats of formation
• fluoroformyl nitrite isomers

Acknowledgement

This research was funded by the Ministry of Higher Education, Science, and Technology of Slovenia, program grant number P2-0148.