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Chapter 1Hydrogen Bonds of Hydrides and Specif i cInteractions of Alkyl Compounds of MainGroup Elements1.1 Hydrogen Bond Energies of Main Group ElementHydridesBorane molecules and alkyl boron have an equilateral planar trigonal structure,with an angle of 120 ? between ligands. Based on the comparative analysis by Cvitas ˇet al. of the electron structure of isostructural molecules of diborane and ethylenemolecules based on the photoelectron spectra and nonempirical calculations [1],Nefedov and Vovna [2] remark that signif i cant differences are present in the natureof the МО for the 1b 2u orbital, the orbital of π-type ethylene, and bridgehead B–H!B in the diborane molecule. Observed changes in the binding type of the 1b 2uorbital are accompanied by its stabilization by 4.2 eV in relation to the 1(π)molecule С 2 H 4 . Shifts of the photoelectron band at the level of s-type 1a g and1b 2u at values of 3.0 and 2.1 eV, respectively, as well as the levels of p-type 1b 2g ,2a g , and 1b 1u at 1.0, 1.5, and 2.1 eV, respectively, are correlated with the energychange due to ionization of the 2s and 2p electrons of carbon and boron atoms. Asdescribed by Bieri et al. [3], the electron population of atomic orbitals of s-3.137e,2p x , 2p y -0.902, 2p z -0e, and hydrogen 1s-1.20e in molecules of BH 3 , points to theinsignif i cant negative charge at the hydrogen atom and its low donor properties inthe formation of intermolecular hydrogen bonds in crystalline and liquid borane(Fig. 1.1). The planar structure of the borane molecule with six coordinated boronatoms forms a volumetric chain structure wherein, under the inf l uence of theformed hydrogen bonds, the boron atoms are out of the plane and located at theapex of the mild trigonal pyramid. The chains are crosslinked by the hydrogen andboron atoms of the contacting chains due to hydrogen bond formation. Breakage ofthe seven hydrogen bonds in the vaporization process, with the transition to thevapor state of diborane, is accompanied by a reduction in the coordinated number ofboron atoms from six to four, which is ref l ected by the stabilization of the tworemaining intermolecular hydrogen bonds DB–H!B in the structure of thediborane molecule.© Springer International Publishing Switzerland 2015A.K. Baev, Specif i c Intermolecular Interactions of Element-Organic Compounds,DOI 10.1007/978-3-319-08563-0_11