Chapter 14 of the Proceedings of the NATO Advanced Research Workshop on Physical-Chemical Properties from Weak Interactions. Erice, Italy, 23-29 May 2001. / Though the hydrogen bond (H-bond) is known since 1920 and in spite of the extraordinary number of books and scientific papers dedicated to it, all attempts to predict its geometry and energetics from the simple knowledge of the chemical structure of the interacting molecules have been so far unsuccessful, a question we have sometimes indicated as the H-bond puzzle. A recent advance in the solution of this problem is represented by the Electrostatic-CovalentH-Bond Model (ECHBM) according to which (i) weak H-bonds are electrostatic in nature but become increasingly covalent with increasing strength, very strong bonds being essentially three-centre-four-electron covalent bonds; (ii) strong and very strong H-bonds may belong only to a limited number of classes which are three for X-H...X homonuclear and four for X-H...Y heteronuclear H-bonds; (iii) within each class, H-bonds are the stronger the smaller is DeltaPA, the difference between the proton affinities of the H-bond donor and acceptor atoms. It is shown that this model leads to an exhaustive classification of all H-bonds in chemical classes which, in turn, becomes a base for the prediction of H-bond strength starting from the chemical structures of the interacting molecules.
Hydrogen Bond at the Dawn of the XXI Century. New Methods, New Results, New Ideas
GILLI, Paola;GILLI, Gastone
2002
Abstract
Chapter 14 of the Proceedings of the NATO Advanced Research Workshop on Physical-Chemical Properties from Weak Interactions. Erice, Italy, 23-29 May 2001. / Though the hydrogen bond (H-bond) is known since 1920 and in spite of the extraordinary number of books and scientific papers dedicated to it, all attempts to predict its geometry and energetics from the simple knowledge of the chemical structure of the interacting molecules have been so far unsuccessful, a question we have sometimes indicated as the H-bond puzzle. A recent advance in the solution of this problem is represented by the Electrostatic-CovalentH-Bond Model (ECHBM) according to which (i) weak H-bonds are electrostatic in nature but become increasingly covalent with increasing strength, very strong bonds being essentially three-centre-four-electron covalent bonds; (ii) strong and very strong H-bonds may belong only to a limited number of classes which are three for X-H...X homonuclear and four for X-H...Y heteronuclear H-bonds; (iii) within each class, H-bonds are the stronger the smaller is DeltaPA, the difference between the proton affinities of the H-bond donor and acceptor atoms. It is shown that this model leads to an exhaustive classification of all H-bonds in chemical classes which, in turn, becomes a base for the prediction of H-bond strength starting from the chemical structures of the interacting molecules.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
