Proton Transfers in Hydrogen-Bonded Systems

CPET usually takes place in H-bonded systems. In such systems we have to take into consideration the presence of the H-bond 

The formation of the H-bond can be regarded as an advancement along the reaction coordinate/ making ha 1 and hb 0. The bond orders of the H-bonded reactant and product complexes can be related to the corresponding bond lengths in the same form as eqn (2.8), 

The LS potential relates the H-bond binding energies (Dab) to the AB equilibrium distances (/AB,eq) and to AB stretching frequency (i ab) in the B H-A hydrogen-bonded complex. It is the sum of four terms  

The first two terms represent the covalent interactions present in the H-bond and have the forms 

The H-A bond is essentially a slightly stretched HA bond and the corresponding harmonic force constant (/ha) equilibrium bond length (/nA.eq) and binding energy (Dha) can be taken from the isolated molecule. However, for the B - - H bond the quantities /hb+ /HB+,eq and Dhb+ are not readily 

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Bell, R.L. and T.N. Truong. 1994. Direct ab initio dynamics studies of proton transfer in hydrogen-bond systems. J. Chem. Phys. 101, 10442. 

S. Scheiner, Proton transfers in hydrogen-bonded systems. 4. cationic dimers of NH3 and O H2 3. J. Phys. Chem. 86, 376-382 (1982)... 

Scheiner, S., Proton transfers in hydrogen bonded systems. Cationic oligomers of water, J. Am. Chem. Soc. 103, 315-320 (1981). 

T. Bountis, ed., Proton Transfer in Hydrogen-Bonded Systems", Plenum Press. New York (1992). 

Proton transfer in hydrogen bonded systems, Ed. T. Bountis, NATO ASI Series, B Physics 291, Plenum, New York, 1992. 

The previous studies of concerted hydrogen atom and proton transfer in hydrogen-bonded systems have been limited to studies of reaction pathways for simple model systems [4-8] with simple, reduced dimensionality methods for including quantum tunneling [13,14,34,35]. The applicability of modem computational methods to such systems is exemplified by more recent studies of the energetics of intramolecular hydrogen atom transfer in molecules such as malonaldehyde [36-39] and models of... 

See, N.A. Dencher, G. Boldt, J. Heberle, H.-D. Hdltje and M. Hditje, in T. Bounds (Ed.), Proton-Transfer in Hydrogen-Bonded Systems, NATO ASI, Ser. B, Vol. 291, Plenum Press, 1992, pp. 171-186. On p. 180 of this paper there is a diagram of a computer-graphics model of the pathways for protons across bacteriorhodopsin. 

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