Is the intramolecular hydrogen bond energy valuable from internal rotation barriers

Abstract A method for evaluating the energy of intramolecular hydrogen bridges utilizing the rotation barriers of the donor and/or of the acceptor groups is proposed. The procedure has been tested successfully on various molecules containing O–H⋯O, O–H⋯Halogen, O–H⋯N, N–H⋯O, N–H⋯N and O–H⋯S bridges. Comparison between the obtained results and those coming from the classic method (Δ E between the open and chelate conformations) shows good agreement and reliability. Failure has been noted only for the S–H⋯O and S–H⋯S hydrogen bridges.