CN rotational barrier, MP4 and CCSD(T) energies of formohydrazide and formohydroxamic acid and vibrational spectral analysis of the hydrazide

The CN internal rotations in formohydrazide OHCNHNH2 and formohydroxamic acid OHCNHOH were investigated at the B3LYP/6-311+G** and MP2/6-311+G** levels of theory. The CN rotational barrier in the molecules was calculated to be about 28–30 kcal/mol. The energies of the molecules were calculated at the B3LYP, MP2, MP4(SDTQ) and CCSD(T) levels of theory with both 6-311G** and 6-311+G** basis sets. From the calculations at all the levels formohydroxamic acid was predicted to exist predominantly in a non-planar near-cis conformation at ambient temperature. From all the calculations formohydrazide was predicted to have a planar cis–syn (CO and NN bonds eclipse each other and NH2 moiety is syn to CN bond) conformation as the lowest energy structure. The NH2 inversion barrier in formohydrazide was predicted to be about 5–7 kcal/mol. The vibrational frequencies of the cis–syn formohydrazide were computed at the B3LYP/6-311+G** level and normal coordinate calculations were carried out. Complete vibrational assignments were made on the basis of normal coordinate analyses and experimental infrared and Raman data of the molecule.