Why are Hydrogen Bonds Directional?

详细信息    查看全文

• 作者：ABHISHEK SHAHI ; ELANGANNAN ARUNAN
• 关键词：Hydrogen Bonding ; non ; covalent interactions ; hydrogen bond angle ; atoms in molecules theory ; electron density topology
• 刊名：Journal of Chemical Sciences
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：128
• 期：10
• 页码：1571-1577
• 全文大小：841 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Chemistry
  
• 出版者：Springer India
• ISSN：0973-7103
• 卷排序：128

文摘

The recent IUPAC recommendation on the definition of hydrogen bonding points out that directionality is a defining characteristic of a hydrogen bond and the angle ∠X-H-Y is generally linear or 180∘. It also suggests that the X-H⋯Y angle be greater than 110∘ for an interaction to be characterized as a hydrogen bond but does not provide any rationale for the same. This article reports a rationale for limiting the angle, based on the electron density topology using the quantum theory of atoms in molecules. Electron density topology for common hydrogen bond donors HF, HCl, HBr, HNC, HCN and HCCH are reported in this work. These calculations lead to an interesting observation that the atomic basins of H atom in all these donor molecules are limited justifying the restriction of hydrogen bond angle. Moreover, similar analysis on some hydrogen bonded complexes confirms that beyond this angle the acceptor atom Y starts interacting with the atomic basin on X. However, conclusions based on bond lengths and angles have to be treated with care and as the IUPAC recommendation points out that independent ‘evidence for bond formation’ in every case is important.