Three computational mise‐en‐scènes of red‐ and blue‐shifted hydrogen bonding motifs: Concept of negative intramolecular coupling—What else?

Abstract

This work is a kind of attempt to rethink some problems which are related to the blue-shifted "hydrogen bonds" and which have been left in the past decade as not yet fully resolved. The impetus for such rethink is originated from the three computational mise-en-scènes on red-and blue-shifted hydrogen bonding motifs, which are aimed to be thoroughly studied in this work, thus resolving the above problems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 104 -119, 2010 Key words: hydrogen bond; red shift; blue shift; proton affinity; deprotonation enthalpy Correspondence to: E. S. Kryachko; e-mail: eugene.kryachko@ulg. ac.be Eugene S. Kryachko: On leave from Department of Chemistry, University of Liege, 4000 Liege, Belgium and Department of Molecular Biophysics (B020), German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany.The Proceedings of the NATO ARW dedicated to A. S. Davydov (June 8 -12, Kiev, Ukraine). To gauge the whenness of being either red or blue. 1 International Journal of Quantum Classical Red-Shifted Hydrogen BondingT ill the 1999, the edge of the 20th century, the hydrogen bonding interaction has been thought as the phenomenon [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] that is rather broadly studied during this nearly entire century. 2 It is, precisely speaking, the phenomenon that manifests in the formation of a so called classical or conventional hydrogen bond.3 According to Pimentel and McClellan [2] (see also [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]), "a hydrogen bond is said to exist when (1) there is evidence of a bond, and (2) there is evidence that this bond sterically involves a hydrogen atom already bonded to another atom."The above definition presumes that a conventional hydrogen bond is the result of some attractive interaction-a so called hydrogen bonding interaction-between at least three "parties" displayed in Scheme 1. 4 One "party" is a proton donor atom or molecule X that "owned" in the past the bonded hydrogen atom H, casting as a second party as the hydron H ␦ (0 Ͻ ␦ Յ 1), and donates it to the third party-a proton acceptor group Y. Y, while interacting with the X-H and thus sharing H ␦ with X or "bridging" X via H ␦ , yields the X-H⅐⅐⅐Y hydrogen bond which, in turn, predetermines the complexation of these three parties into the hydrogen-bonded complex. If X and Y are merely atoms, X-H⅐⅐⅐Y is geometrically characterized by the bond length R(X-H), the H-bond separation r(H⅐⅐⅐Y) defined as the distance between the bridging proton and the proton acceptor Y and often referred to as the H-bond length, and the bond angle Є XHY.According to the generally accepted definition, the H-bond X-H⅐⅐⅐Y is formed iff the following necessary and sufficient conditions are obeyed [1-17]:(i) There exists a clear evidence of the bond formation-this can be, for example, the appearance of the H-bond stretching mode n s (X⅐⅐⅐Y) together with another two new vibrational modes if Є XHY ϭ 180°and one otherwise; (ii) There exists a clear evid...

Theoretical investigation of the conformation, acidity, basicity and hydrogen bonding ability of halogenated ethers

“…42 Similarly, protonation at the F atom of F 2 NH also leads to a break down of the NF bond. 43 As expected from the basicity of the molecules, the OH + distances slightly increase from 0.973 to 0.982 A ˚and the n(OH + ) decrease from 3745 to 3633 cm À1 upon halogen substitution.…”

“…The weak proton donor ability of the CH bond has also been suggested by the fact that despite its large DPE (413 kcal mol À1 ), it is able to form weak cyclic homodimers characterized by CHÁ Á ÁO hydrogen bonds. 18,[43][44][45] In this cyclic dimer stabilized by three hydrogen bonds, the intermolecular distances calculated at the MP2/6-311++G(d,p) level are between 2.52 and 2.60 A ˚and the binding energy including the BSSE-correction is equal to À2.30 kcal mol À1 . 45 The SAPT analysis (Table 4) shows that in the a-and b-type complexes, the electrostatic term represents about 60% of the total attraction forces, while the induction and dispersion components represent about 8 and 30%, respectively.…”

Theoretical studies on hydrogen bonding interactions: From small clusters to the liquid phase

“…Also, ab initio calculations of CO 2 complexes with simple model carbonyl compounds identified the possibility of a weaker CH···O interaction that acts cooperatively with the Lewis acid–base interaction having hydrogen atoms attached to the α‐carbon or the carbonyl106. However, as noticed by Kryachko, there are still problems that are related to these systems and that are awaiting their complete understanding54. In particular, other small molecules possessing electron deficient carbon atoms, e.g., HCN and FCN, are also candidates for working as Lewis acids in the presence of carbonyl compounds34.…”

“…Weaker than a conventional covalent bond, the H‐bond is stronger than van der Waals interactions that bind together nonpolar molecules. Strictly speaking, X can be an atom like O, F, or N, whereas Y can be any σ or π electron donor site (e.g., a Lewis base) in the same or separate molecule52–54. Recently, metal atom gold has been proposed as a nonconventional proton acceptor55.…”

“…As usual, all species are taken in their fully optimized geometries. Hence, changes in the internal geometries of both XH and Y can lead to significant nuclear relaxation after the H‐bond formation54.…”