Ab initio calculations at the post Hartree–Fock level (MP2) have been used for a complete study of molecular structures of all possible conformations of 4-amino-3-penten-2-one (APO) to obtain the order of stability and relative hydrogen bond strength in four of the conformers. The comparison of energies for different species indicates that non-H bonded ketoenamine conformers are about 47 kJ/mol more stable than non-H bonded enolimine conformers. The stability of ketoenamine over enolimine reduces to 23.6 kJ/mol for the H-bonded ketoenamine/enolimine pair due to the stronger H-bond in enolimine conformers. The contribution of resonance to the stability of hydrogen bonding in ketoenamine is estimated to be around 16 kJ/mol.

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