C{single bond}N rotational barrier, MP4 and CCSD(T) energies of formohydrazide and formohydroxamic acid and vibrational spectral analysis of the hydrazide

The C{single bond}N internal rotations in formohydrazide OHC{single bond}NH{single bond}NH₂ and formohydroxamic acid OHC{single bond}NH{single bond}OH were investigated at the B3LYP/6-311+G** and MP2/6-311+G** levels of theory. The C{single bond}N 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 (C{double bond, long}O and N{single bond}N bonds eclipse each other and NH₂ moiety is syn to C{single bond}N 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.