Homonuclear versus Heteronuclear Resonance-Assisted Hydrogen Bonds: Tautomerism, Aromaticity, and Intramolecular Hydrogen Bonding in Heterocyclic Systems with Different Exocyclic Proton Donor/Acceptor

详细信息    查看全文

• 作者：Roman I. Zubatyuk^† ; ; Oleg V. Shishkin*^† ; ^&#8225 ; ; Leonid Gorb^&#8225 ; ^§ ; ; Jerzy Leszczynski^&#8225 ;
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：March 26, 2009
• 年：2009
• 卷：113
• 期：12
• 页码：2943-2952
• 全文大小：216K
• 年卷期：v.113,no.12(March 26, 2009)
• ISSN：1520-5215

文摘

Tautomerism and resonance-assisted hydrogen bonding have been analyzed on the basis of the results of ab initio calculations at the MP2/AUG-cc-pVDZ level of theory for the series of molecules containing different heterocycles connected with resonance spacer and containing different exocyclic proton donor/acceptor atoms. It is demonstrated that the position of tautomeric equilibrium is controlled mainly by two factors: aromaticity of heterocycle, which could be different for two tautomers, and relative proton affinities of two heteroatoms forming a hydrogen bond. Replacement of exocyclic proton donor/acceptor atom results in change of an aromaticity degree of heterocycle leading to alteration of relative stability of tautomers. Comparison of structure and properties of E and Z conformers of molecules demonstrates resonance-assisted character of intramolecular hydrogen bond. Application of the NBO theory reveals that the π-component of the electron density within resonant spacer plays the primary role for determination of characteristics of hydrogen bond while σ-skeleton only reflects the π-polarization. An analysis of strength of intramolecular hydrogen bond using geometrical, energetic, and AIM and NBO parameters indicates that the homonuclear N···H−N hydrogen bond is considerably weaker than heteronuclear N···H−O and N···H−S hydrogen bonds in the case of the XH tautomers.