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Low‐barrier hydrogen bonds: Ab initio and DFT investigation
Author(s) -
Kumar Ganesh A.,
Pan Yongping,
Smallwood C. Jay,
McAllister Michael A.
Publication year - 1998
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/(sici)1096-987x(199809)19:12<1345::aid-jcc3>3.0.co;2-i
Subject(s) - chemistry , hydrogen bond , enthalpy , low barrier hydrogen bond , ab initio , hydrogen , bond strength , formate , computational chemistry , bond order , acceptor , bond energy , bond length , molecule , catalysis , thermodynamics , organic chemistry , physics , adhesive , layer (electronics) , condensed matter physics
High‐level ab initio and DFT molecular orbital calculations have been used to investigate the physical properties of a model low‐barrier hydrogen bond (LBHB) system: formic acid–formate anion. In the gas phase, it is found that the hydrogen bond formed is extraordinarily short and strong [ca. 27 kcal/mol at B3LYP/6‐31++G(d, p)], with a calculated enthalpy of activation for proton transfer from donor to acceptor that is less than the zero‐point vibrational energy available to the system. Several perturbations to this system were studied. Forcing a mismatch of p K a s between donor and acceptor, via the use of substituents, causes the strength of the hydrogen bond to decrease. Microsolvation of the hydrogen‐bonded complex does not affect the strength of the low‐barrier hydrogen bond very much. Small variations in the structure of the LBHB results in a decrease in hydrogen‐bond strength. Increasing the effective polarity of the cavity surrounding the LBHB was found to have a significant impact on the strength of the hydrogen bond. Implications for enzyme catalysis are discussed. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1345–1352, 1998