Theoretical investigation of the gas phase tautomerization of sarcosine

The proton transfer reaction involving the neutral intramolecular hydrogen bonded conformer of sarcosine (N-methylglycine), Iu, to form the zwitterion ic tautomer, Iz, was analyzed by theoretical chemistry. Ab initio calculati ons show that the zwitterionic conformer Iz, is a minimum at all RHF levels of theory examined. The formation of Iz involves a proton transfer from Iu to form Iz, via a transition state, which is zwitterionic like. Form the R HF/6-311++G** calculations, the activation barrier for the tautomerization is 91.7 kJ/mol, and the energy difference between Iz and the transition sta te, Its, is 1.9 kJ/mol. Zwitterion Iz reverts to the unionized tautomer at levels of theory which include electron correlation. (C) 1999 Elsevier Scie nce B.V. All rights reserved.