NONCONVENTIONAL HYDROGEN-BONDS

Hydrogen bonds (HBs) are the most important 'weak' interactions encoun tered in solid, liquid and gas phases, The HE can be defined as an att ractive interaction between two molecular moieties in which at least o ne of them contains a hydrogen atom that plays a fundamental role, Cla ssical HBs correspond to those formed by two heteroatoms, A and B, wit h a hydrogen atom bonded to one of them and located approximately in b etween (A-H ... B). Recently, knowledge of the number of functional gr oups which act as hydrogen bond donors or accepters has increased cons iderably and most of these new groups are discussed.