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...