The effect of methyl group on the cooperativity between three types of hydrogen bond: O[BOND]H···O, C[BOND]H···O, and O[BOND]H···π

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Abstract

The effect of the methyl group on the cooperativity between three types of hydrogen bond (O[BOND]H···O, C[BOND]H···O, and O[BOND]H···π) in cyclic complex involving an acetylene and two waters has been studied on the basis of high-level ab initio calculations. The total interaction energy of three hydrogen bonds increases as the number of methyl group in the complex increases. The binding distances of O[BOND]H···π and O[BOND]H···O hydrogen bonds shorten, while that of C[BOND]H···O hydrogen bond elongates with increasing methyl group. This indicates that addition of methyl group leads to enhancement of O[BOND]H···π and O[BOND]H···O hydrogen bonds, and weakening of C[BOND]H···O hydrogen bond, as also shown in frequency shift, chemical shifts, charge populations, and stabilization energies of orbital interactions. Although the presence of methyl group has a complicated effect on different type of hydrogen bond, the cooperativity of three hydrogen bonds increases in general with the addition of methyl group. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

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