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.