{"id":7085,"date":"2013-02-20T15:20:08","date_gmt":"2013-02-20T13:20:08","guid":{"rendered":"http:\/\/www.ehu.es\/chemistry\/theory\/?p=7085"},"modified":"2018-02-27T22:32:57","modified_gmt":"2018-02-27T20:32:57","slug":"hydrogen-bond","status":"publish","type":"post","link":"https:\/\/www.ehu.eus\/chemistry\/theory\/5_kt-seminars\/hydrogen-bond\/","title":{"rendered":"Hydrogen bond"},"content":{"rendered":"<p><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">The hydrogen bond (HB) is the subject of various studies since it is important in numerous chemical, physical and biological processes.<\/span><\/span><a href=\"#sdendnote1sym\" name=\"sdendnote1anc\"><\/a><sup>i<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote2sym\" name=\"sdendnote2anc\"><\/a><sup>ii<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote3sym\" name=\"sdendnote3anc\"><\/a><sup>iii<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote4sym\" name=\"sdendnote4anc\"><\/a><sup>iv<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> One of first definitions of the hydrogen bond was given by Pauling <\/span><\/span><a href=\"#sdendnote5sym\" name=\"sdendnote5anc\"><\/a><sup>v<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> who stated that \u201c<\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>under certain conditions an atom of hydrogen is attracted by rather strong forces to two atoms, instead of only one, so that it may be considered to be acting as a bond between them. This is called the hydrogen bond\u201d. <\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">This interaction may be designated as X-H\u2026Y, where X-H is the proton donating bond while Y is the proton acceptor. Pauling pointed out that X and Y atoms should be characterized by the high electronegativity, that the Y proton acceptor should posses at least one free electron pair and that the hydrogen bond is the electrostatic interaction. <\/span><\/span><\/span><\/span><\/p>\n<p><a name=\"_Ref329172345\"><\/a><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Numerous characteristics and properties of the hydrogen bond have been presented. One can mention the elongation of the X-H bond as a result of hydrogen bond formation and a concomitant decrease of the X-H stretch vibration frequency.<\/span><\/span><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">1<\/span><\/span><\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> This shift to lower frequencies is called a red shift and being experimentally detectable in gas, liquid and solid phase was treated as the strong evidence of the hydrogen bond formation. The X-H\u2026Y angle close to 180<\/span><\/span><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">0<\/span><\/span><\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> and the H\u2026Y distance smaller than the corresponding sum of van der Waals radii are also attributed to the hydrogen bond characteristics.<\/span><\/span><a href=\"#sdendnote6sym\" name=\"sdendnote6anc\"><\/a><sup>vi<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> However the subsequent studies have shown that there are interactions similar or related to the hydrogen bond which posses few of its characteristics but usually not all. The statement of the high electronegativity of X and Y atoms was contested since the C-H\u2026O, C-H\u2026N and C-H\u2026S interactions were analyzed and classified as the hydrogen bonds;<\/span><\/span><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">6<\/span><\/span><\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote7sym\" name=\"sdendnote7anc\"><\/a><sup>vii<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> even the existence of the C-H\u2026C hydrogen bond was discussed.<\/span><\/span><a href=\"#sdendnote8sym\" name=\"sdendnote8anc\"><\/a><sup>viii<\/sup><\/span><\/span><\/p>\n<p><a name=\"_Ref329243992\"><\/a><a name=\"_Ref329243995\"><\/a> <span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">The dihydrogen bond (DHB) is the special type of the hydrogen bond where the role of the proton acceptor plays another hydrogen atom which is negatively charged.<\/span><\/span><a href=\"#sdendnote9sym\" name=\"sdendnote9anc\"><\/a><sup>ix<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote10sym\" name=\"sdendnote10anc\"><\/a><sup>x<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> The X-H\u2026Y interactions where the complexation leads to the shortening of the X-H bond and the accompanying increase of the X-H stretch vibration frequency (blue shift) were also analyzed.<\/span><\/span><a href=\"#sdendnote11sym\" name=\"sdendnote11anc\"><\/a><sup>xi<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> Thus one of the previously pointed out evidences of the existence of the hydrogen bond, the elongation of the proton donating bond, often treated as its signature was also contested. <\/span><\/span><\/span><\/span><\/p>\n<p><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">The X-H\u2026\u03c0 interactions were analyzed and it was pointed out that they often posses characteristics of the hydrogen bond.<\/span><\/span><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">3<\/span><\/span><\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote12sym\" name=\"sdendnote12anc\"><\/a><sup>xii<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote13sym\" name=\"sdendnote13anc\"><\/a><sup>xiii<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> Thus the existence of one-center proton acceptor possessing at least one free electron pair is also denied as the feature attributed to the hydrogen bond since \u03c0-electrons delocalized between two or more atoms are the proton acceptor for the X-H\u2026\u03c0 interactions. <\/span><\/span><\/span><\/span><\/p>\n<p><a name=\"_Ref329504781\"><\/a> <span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">The recent definition of Arunan and co-workers,<\/span><\/span><a href=\"#sdendnote14sym\" name=\"sdendnote14anc\"><\/a><sup>xiv<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> covers a diversity of interactions often classified as the hydrogen bonds. It is as follows: <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>\u201cthe<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em> hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X\u2013H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>\u201d. <\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">This definition only slightly differs from the older one of Pimentel and McClellan <\/span><\/span><a href=\"#sdendnote15sym\" name=\"sdendnote15anc\"><\/a><sup>xv<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> however it contains additional lists of criteria, characteristics and footnotes which refer to systems classified in numerous studies as the hydrogen bonds. For example it is stated that <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>\u201cthe<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em> acceptor is an electron rich region such as, but not limited to, a lone pair of Y or \u03c0-bonded pair of Y-Z<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>\u201d. <\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">In such a sense the X-H\u2026\u03c0 interaction is in agreement with this explanation. <\/span><\/span><\/span><\/span><\/p>\n<p><a name=\"_Ref329252929\"><\/a><a name=\"_Ref329252931\"><\/a> <span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">New experimental techniques and theoretical methods which allow to analyze inter- and intramolecular interactions were introduced in last decades. One can mention the Quantum Theory of Atoms in Molecules (QTAIM) <\/span><\/span><a href=\"#sdendnote16sym\" name=\"sdendnote16anc\"><\/a><sup>xvi<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote17sym\" name=\"sdendnote17anc\"><\/a><sup>xvii<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> which is a powerful tool to analyze the electron density of any molecular system and so on the properties of interactions in terms of the characteristics of the electron density. The Natural Bond Orbitals (NBO) method is another tool to analyze different interactions.<\/span><\/span><a href=\"#sdendnote18sym\" name=\"sdendnote18anc\"><\/a><sup>xviii<\/sup><sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">,<\/span><\/span><\/sup><a href=\"#sdendnote19sym\" name=\"sdendnote19anc\"><\/a><sup>xix<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> The hydrogen bond formation, in terms of the NBO method, may be considered as the combination of two processes.<\/span><\/span><a href=\"#sdendnote20sym\" name=\"sdendnote20anc\"><\/a><sup>xx<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> The hyperconjugative interaction connected with the charge transfer from the Y-lone pair to the \u03c3*(X-H) antibonding orbital. This is connected with the increase of the occupation of that orbital and it leads to the elongation of the X-H bond. The second process is connected with the increase in s-character of X hybrid orbital in the X-H bond and it is responsible for the shortening of the X-H bond. If the second effect outweighs the first one thus the blue shift of the X-H stretch vibration frequency is observed, in the other case the more common red shift hydrogen bond exists. <\/span><\/span><\/span><\/span><\/p>\n<p><a name=\"_Ref329254310\"><\/a> <span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">On a basis of NBO analyses and findings the following definition was proposed recently by Weinhold and Klein.<\/span><\/span><a href=\"#sdendnote21sym\" name=\"sdendnote21anc\"><\/a><sup>xxi<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>Hydrogen bond: A <\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em><span style=\"text-decoration: underline;\">fractional<\/span><\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em> chemical bond of coordinative A\u2013H\u2026B Lewis acid\u2013base type, associated with the partial intermolecular A\u2013H\u2026:B \uf0ab A:\u2026H\u2013B resonance (3-center\/4-electron proton-sharing) commonly originating in the n<\/em><\/span><\/span><sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>B<\/em><\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em> \uf0ae \u03c3*<\/em><\/span><\/span><sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>AH<\/em><\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>donor\u2013acceptor interaction between the lone pair n<\/em><\/span><\/span><sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>B<\/em><\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>of the Lewis base and the hydride antibond <\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>\u03c3*<\/em><\/span><\/span><sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>AH<\/em><\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>of the Lewis acid.<\/em><\/span><\/span><a href=\"#sdendnote22sym\" name=\"sdendnote22anc\"><\/a><sup>xxii<\/sup><\/span><\/span><\/p>\n<p><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> Two kinds of interactions are analyzed here; the dihydrogen bond which was also previously considered as the X-H\u2026\u03c3 interaction <\/span><\/span><a href=\"#sdendnote23sym\" name=\"sdendnote23anc\"><\/a><sup>xxiii<\/sup><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> and the interaction where molecular hydrogen acts as the Lewis base, designated later as X-H\u2026\u03c3(H<\/span><\/span><sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">2<\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">). <\/span><\/span><\/span><\/span><\/p>\n<p id=\"sdendnote1\"><span style=\"font-size: small;\">i<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Jeffrey, G. A.; Saenger, W. <\/span><span style=\"font-size: medium;\"><em>Hydrogen Bonding in Biological Structures<\/em><\/span><span style=\"font-size: medium;\">, Springer-Verlag: Berlin, <\/span><span style=\"font-size: medium;\"><strong>1991<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/p>\n<p><span style=\"font-size: small;\">ii<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Scheiner, S. <\/span><span style=\"font-size: medium;\"><em>Hydrogen Bonding: A Theoretical Perspective<\/em><\/span><span style=\"font-size: medium;\">, Oxford University Press: New York, <\/span><span style=\"font-size: medium;\"><strong>1997<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/p>\n<div id=\"sdendnote3\"><span style=\"font-size: small;\">iii<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Desiraju, G.R.; Steiner T. <\/span><span style=\"font-size: medium;\"><em>The weak hydrogen bond in structural chemistry and biology<\/em><\/span><span style=\"font-size: medium;\">; Oxford University Press Inc., New York, <\/span><span style=\"font-size: medium;\"><strong>1999<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/div>\n<div id=\"sdendnote4\"><span style=\"font-size: small;\">iv<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\"><em>Hydrogen Bonding \u2013 New Insights<\/em><\/span><span style=\"font-size: medium;\">, Ed. Grabowski, S.J. Vol.3 of the series: Challenges and Advances in Computational Chemistry and Physics, Ed. Leszczynski, J. Springer, Dordrecht, <\/span><span style=\"font-size: medium;\"><strong>2006<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/div>\n<div id=\"sdendnote5\"><span style=\"font-size: small;\">v<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Pauling L. <\/span><span style=\"font-size: medium;\"><em>The Nature of the Chemical Bond, Cornell University Press<\/em><\/span><span style=\"font-size: medium;\">, Ithaca, New York, 3<\/span><sup style=\"font-size: small;\"><span style=\"font-size: medium;\">rd<\/span><\/sup><span style=\"font-size: medium;\"> edition, <\/span><span style=\"font-size: medium;\"><strong>1960<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/div>\n<div id=\"sdendnote6\"><span style=\"font-size: small;\">vi<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Taylor, R.; Kennard, O. Crystallographic Evidence for the Existence of C-H\u2026O, C-H\u2026N, and C-H\u2026Cl Hydrogen Bonds. <\/span><span style=\"font-size: medium;\"><em>J.Am.Chem.Soc<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>1982<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>104<\/em><\/span><span style=\"font-size: medium;\">, 5063-5070.<\/span><\/span><\/div>\n<div id=\"sdendnote7\"><span style=\"font-size: small;\">vii<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Suttor, D. J. Evidence for the Existence of C-H\u2026O Hydrogen Bonds in Crystals. <\/span><span style=\"font-size: medium;\"><em>J. Chem. Soc.<\/em><\/span><span style=\"font-size: medium;\"><strong>1963<\/strong><\/span><span style=\"font-size: medium;\">, 1105-1110.<\/span><\/span><\/div>\n<div id=\"sdendnote8\"><span style=\"font-size: small;\">viii<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Mueller-Westerhoff, U.T.; Nazzal, A.; Proessdorf, W. First evidence for the existence of intramolecular carbon-hydrogen-carbon hydrogen bonds: carboanions of [1.1]ferrocenophane, 1-methyl-[1.1]ferrocenophane, and 1,12-dimethyl-[1.1]ferrocenophane. <\/span><span style=\"font-size: medium;\"><em>J.Am.Chem.Soc. <\/em><\/span><span style=\"font-size: medium;\"><strong>1982<\/strong><\/span><span style=\"font-size: medium;\">, 103, 7678-7681.<\/span><\/span><\/div>\n<div id=\"sdendnote9\"><span style=\"font-size: small;\">ix<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Wessel, J.; Lee, Jr., J. C.; Peris, E.; Yap, G. P. A.; Fortin, J. B.; Ricci, J. S.; Sini, G.; Albinati, A.; Koetzle, T. F.; Eisenstein, O.; Rheingold, A. L.; Crabtree, R. H. An Unconventional Intermolecular Three-Center N-H&#8230;H<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">2<\/span><\/sub><span style=\"font-size: medium;\">Re Hydrogen Bond in Crystalline [ReH<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">5<\/span><\/sub><span style=\"font-size: medium;\">(PPh<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">3<\/span><\/sub><span style=\"font-size: medium;\">)<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">3<\/span><\/sub><span style=\"font-size: medium;\">]-indole-C<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">6<\/span><\/sub><span style=\"font-size: medium;\">H<\/span><sub style=\"font-size: small;\"><span style=\"font-size: medium;\">6<\/span><\/sub><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><em>Angew. Chem. Int. Ed. Engl<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>1995<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>34<\/em><\/span><span style=\"font-size: medium;\">, 2507-2509.<\/span><\/div>\n<div id=\"sdendnote10\"><span style=\"font-size: small;\">x\u00a0<span style=\"font-size: medium;\">Crabtree R. H.; Siegbahn, P. E .M.; Eisenstein, O.; Rheingold, A. L.; Koetzle, T. F. A New Intermolecular Interaction: Unconventional Hydrogen Bonds with Element-Hydride Bonds as Proton Acceptor. <\/span><span style=\"font-size: medium;\"><em>Acc. Chem. Res<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>1996<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>29<\/em><\/span><span style=\"font-size: medium;\">, 348-354.<\/span><\/span><\/div>\n<div id=\"sdendnote11\"><span style=\"font-size: small;\">xi<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Hobza, P.; Havlas, Z. Blue-Shifting Hydrogen Bonds. <\/span><span style=\"font-size: medium;\"><em>Chem. Rev<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>2000<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>100<\/em><\/span><span style=\"font-size: medium;\">, 4253-4264.<\/span><\/span><\/div>\n<div id=\"sdendnote12\"><span style=\"font-size: small;\">xii<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Nishio, M.; Hirota, M.; Umezawa, Y. <\/span><span style=\"font-size: medium;\"><em>The CH\/\uf070 Interaction, Evidence, Nature, and Consequences<\/em><\/span><span style=\"font-size: medium;\">, Wiley-VCH, New York, <\/span><span style=\"font-size: medium;\"><strong>1998<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/span><\/div>\n<div id=\"sdendnote13\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">xiii Takahashi, O.; Kohno, Y.; Nishio, M. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Relevance of Weak Hydrogen Bonds in the Conformation of Organic Compounds and Bioconjugates: Evidence from Recent Experimental Data and High-Level <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>ab Initio<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> MO Calculations. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>Chem.Rev<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">2010<\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>110<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, 6049-6076.<\/span><\/span><\/div>\n<div id=\"sdendnote14\"><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\">xiv\u00a0<span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Arunan, E.; Desiraju, G. R.; Klein, R. A.; Sadlej, J.; Scheiner, S.; Alkorta, I.; Clary, D. C.; Crabtree, R. H.; Dannenberg, J. J.; Hobza, P.; Kjaergaard, H.G.; Legon, A.C.; Mennucci, B.; Nesbitt, D.J. Definition of the hydrogen bond. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>Pure. Appl. Chem.<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><strong>2011<\/strong><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>83<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, 1637-1641.<\/span><\/span><\/span><\/span><\/div>\n<div id=\"sdendnote15\"><span style=\"font-size: small;\">xv<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">G.C.Pimentel, A.L.McClellan, The Hydrogen Bond, W.H.Freeman and Company, San Francisco and London, <\/span><span style=\"font-size: medium;\"><strong>1960<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/span><\/div>\n<div id=\"sdendnote16\"><span style=\"font-size: small;\">xvi<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Bader, R.F.W. Atoms in molecules. <\/span><span style=\"font-size: medium;\"><em>Acc.Chem.Res<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>1985<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>18<\/em><\/span><span style=\"font-size: medium;\">, 9-15.<\/span><\/span><\/div>\n<div id=\"sdendnote17\"><span style=\"font-size: small;\"><a href=\"#sdendnote17anc\" name=\"sdendnote17sym\"><\/a>xvii<\/span> <span style=\"font-size: small;\">\u00a0<\/span><span style=\"font-size: medium;\">Bader, R.F. W. <\/span><span style=\"font-size: medium;\"><em>Atoms in Molecules<\/em><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>A Quantum Theory<\/em><\/span><span style=\"font-size: medium;\">; Oxford University Press, Oxford, <\/span><span style=\"font-size: medium;\"><strong>1990<\/strong><\/span><span style=\"font-size: medium;\">.<\/span><\/div>\n<div id=\"sdendnote18\"><span style=\"font-size: small;\">xviii<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Weinhold, F.; Landis, C. Valency and Bonding, A Natural Bond Orbital Donor \u2013 Acceptor Perspective. Cambridge University Press <\/span><span style=\"font-size: medium;\"><strong>2005<\/strong><\/span><span style=\"font-size: medium;\">. <\/span><\/span><\/div>\n<div id=\"sdendnote19\"><span style=\"font-size: small;\">xix<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">Reed, A.E.; Curtiss, L.A.; Weinhold, F. Intermolecular Interactions from a natural bond orbital, donor-acceptor viewpoint. <\/span><span style=\"font-size: medium;\"><em>Chem.Rev<\/em><\/span><span style=\"font-size: medium;\">. <\/span><span style=\"font-size: medium;\"><strong>1988<\/strong><\/span><span style=\"font-size: medium;\">, <\/span><span style=\"font-size: medium;\"><em>88<\/em><\/span><span style=\"font-size: medium;\">, 899-926.<\/span><\/span><\/div>\n<div id=\"sdendnote20\"><span style=\"font-size: medium;\">xx Alabugin, I.V.; Manoharan, M.; Peabody, S.; Weinhold, F. Electronic Basis of Improper Hydrogen Bonding:\u2009 A Subtle Balance of Hyperconjugation and Rehybridization. <\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>J.Am.Chem.Soc<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">2003<\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>125<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, 5973-5987.<\/span><\/span><\/div>\n<div id=\"sdendnote21\"><span style=\"font-family: Calibri,serif;\"><span style=\"font-size: small;\">xxi\u00a0<span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Weinhold, F.; Klein, R. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">What is a hydrogen bond? Mutually consistent theoretical and experimental criteria for characterizing H-bonding interactions. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>Mol.Phys<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><strong>2012<\/strong><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>110<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, 565-579.<\/span><\/span><\/span><\/span><\/div>\n<div id=\"sdendnote22\"><span style=\"font-size: small;\">xxii<span style=\"font-family: 'Times New Roman', serif;\">\u00a0<\/span><span style=\"font-size: medium;\">\u00a0In this definition the A-H&#8230;B designation is applied for the hydrogen bond interaction, in this Account the term X-H&#8230;Y is used.<\/span><\/span><\/div>\n<div id=\"sdendnote23\"><span style=\"font-size: small;\">xxiii<\/span> <span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Wim T. Klooster, Thomas F. Koetzle, Per E. M. Siegbahn, Thomas B. Richardson, and Robert H. Crabtree, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">Study of the N-H\u2026H-B Dihydrogen Bond Including the Crystal Structure of BH<\/span><\/span><sub style=\"font-family: Calibri, serif; font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">3<\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">NH<\/span><\/span><sub style=\"font-family: Calibri, serif; font-size: small;\"><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">3<\/span><\/span><\/sub><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"> by Neutron Diffraction. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>J.Am.Chem.Soc<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">. <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><strong>1999<\/strong><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, <\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\"><em>121<\/em><\/span><\/span><span style=\"font-family: Times New Roman,serif;\"><span style=\"font-size: medium;\">, 6337-6343.<\/span><\/span><\/div>\n","protected":false},"excerpt":{"rendered":"<p>The hydrogen bond (HB) is the subject of various studies since it is important in numerous chemical, physical and biological processes.i,ii,iii,iv One of first definitions of the hydrogen bond was given by Pauling v who stated that \u201cunder certain conditions an atom of hydrogen is attracted by rather strong forces to two atoms, instead of [&hellip;]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[78],"tags":[],"class_list":["post-7085","post","type-post","status-publish","format-standard","hentry","category-5_kt-seminars"],"blocksy_meta":[],"acf":[],"_links":{"self":[{"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/posts\/7085","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/comments?post=7085"}],"version-history":[{"count":13,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/posts\/7085\/revisions"}],"predecessor-version":[{"id":12162,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/posts\/7085\/revisions\/12162"}],"wp:attachment":[{"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/media?parent=7085"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/categories?post=7085"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ehu.eus\/chemistry\/theory\/wp-json\/wp\/v2\/tags?post=7085"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}