A comparative study on hydrogen bonding ability of thioformohydroxamic acid and formohydroxamic acid

The presence of intra and intermolecular hydrogen bonding interactions has been explored in six tautomeric forms of thioformohydroxamic acid and its 1:1 aggregates with water employing MP2/Aug-cc-pVDZ theoretical level. The intramolecular hydrogen bonding interactions are observed to be present in both the most stable forms of thione and thiol tautomeric forms (1Z and 2Z, respectively). The stabilization energy resulting from aggregation of TFHA with H2O in 1:1 ratio for all the tautomeric forms has been evaluated for different orientations of H2O relative to TFHA. The most stable aggregate has orientation similar to the most stable aggregate of FHA with H2O and the stabilization energy for TFHA is only 0.79 kcal/mol less than the value for FHA at MP2/Aug-cc-pVDZ theoretical level.