Wydział Chemii

Benjamin J. Van der Veken

Wouter A. Herrebout

Roman Szostak

D. Shchepkin

Zdenek Havlas

Pavel Hobza

2001

Journal of the American Chemical Society

123

12290-12293

10.1021/ja010915t

Naukowa

Angielski

Artykuł

In the infrared spectra of solutions in liquid argon of dimethyl ether ((CH₃)₂O) and fluoroform (HCF₃), bands due to a 1:1 complex between these monomers have been observed. The C−H stretch of the HCF₃ moiety in the complex appears 17.7 cm^-1 above that in the monomer, and its intensity decreases by a factor of 11(2). These characteristics situate the interaction between the monomers in the realm of improper, blue-shifting hydrogen bonding. The complexation shifts the C−F stretches downward by some 9 cm^-1, while the C−H stretches in (CH₃)₂O are shifted upward by 9−15 cm^-1, and the C−O stretches are shifted downward by 5 cm^-1. These shifts are in very good agreement with those calculated by means of correlated ab initio methods, and this validates a two-step mechanism for improper, blue-shifting hydrogen bonding. In the first step, the electron density is transferred from the oxygen lone electron pairs of the proton acceptor ((CH₃)₂O) to fluorine lone electron pairs of the proton donor (CHF₃) which yields elongation of all CF bonds. Elongation of CF bonds is followed (in the second step) by structural reorganization of the CHF₃ moiety, which leads to the contraction of the CH bond. It is thus clearly demonstrated that not only the spectral manifestation of H-bonding and improper H-bonding but also their nature differ.

Deformation, Electron density, Monomers, Noncovalent interactions, Stabilization

https://doi.org/10.1021/ja010915t

https://www.acs.org/content/acs/en.html