Effect of Bond Multiplicity upon Hydrogen Bonding and Proton Transfers. Double Bonded Atoms
Journal of the American Chemical Society
American Chemical Society
Ab initio methods are used to study the interactions between H2C=CH2 and H2C=NH and their deprotonated anions. (H2CCH-H-CHCH2)- is the most weakly bound with a complexation energy of 5.6 kcal/mol at the correlated MP2 level as compared to the stronger interaction of 10.3 for (HNCH-H-CHNH)- where the peripheral C atom has been replaced by N. The strongest interaction of 15.4 kcal/mol is observed in (H2CN-H-NCH2)- where N atoms participate directly in the H-bond. (H2CCH-H-CHCH2)- contains the longest intermolecular separation while the N-N distance in the latter complex is the shortest. This separation between subunits undergoes a contraction between 0.5 and 0.9 A as the proton reaches the transfer midpoint. The highest proton transfer barrier of 13 kcal/mol is observed for (H2CCH-H-CHCH2)-. In contrast, the small barrier in (H2CN-H.-NCH2)- is eliminated altogether when zero-point vibrations are considered. Transfer rates are computed using modified RRKM theory. These results are placed within the broader context of other complexes in which the atoms participating in the H-bond are single- and triple-bonded within their respective subunits so as to arrive at systematic conclusions regarding the effects of such multiple bonding upon the energetics of H-bond formation and proton transfer.
Effect of Bond Multiplicity upon Hydrogen Bonding and Proton Transfers. Double Bonded Atoms S. Scheiner, L. Wang J. Am. Chem. Soc. 1992 114 (10), 3650-3655.