Normal Bond Angles Research Articles

Ab initio study of hyperconjugation effects on charge distribution in representative polycyclic alcohols

Ab initio calculations using fully optimized geometries are used to generalize hyperconjugation effects in a representative series of eight polycyclic alcohols. The systems studied include tetra-, penta- and hexa-cyclic structures with varying degrees of tension, due to compression and stretching of carbon-carbon and carbon-hydrogen bonds, and of distortion from normal bond angles as well to differences in van der Waals interactions. These findings indicate, in general, that carbon and hydrogen atoms with the proper spatial alignment relative to a nonbonding oxygen lone pair follow the same general trends as small acyclic alcohols. Results from minimum STO-3G basis-set calculations and the hyperconjugation model can generally distinguish clearly the subtleties of charge and bond length distributions observed in the various conformations of all the polycyclic alcohols investigated.

Structure of (VO) 2P 2O 7

The crystal structure of the vanadium (IV) pyrophosphate that shows the remarkable ability to selectively catalyze the oxidation of butane to maleic anhydride has been accurately determined for the first time. This was facilitated by the growth of high quality (VO) 2P 2O 7 crystals under controlled oxygen fugacity. Single crystal X-ray diffraction indicated monoclinic symmetry rather than the orthorhombic symmetry assumed in earlier studies. The space group is P2 1 with a = 7.28 A ̊ , b = 16.588 A ̊ , c = 9.58 A ̊ , β = 89.975 Å, and Z = 4. A final R of 3.1% was obtained. Typical vanadyl environments are found for all eight crystallographically distinct vanadium atoms, and normal bond angles and distances are found for the P 2O 7 groups.

Vibronic theory of normal and anomalous bond angles in heteroligand complexes with multiply-bonded ligands; osmium and ruthenium nitrosyl complexes

New theoretical problems concerning the geometry of transition metal heteroligand complexes are treated. The recently discovered anomalous bond angles are discussed for [OsNO(NH 3) 4Hal] 2+ complexes where equatorial OsNH 3 bonds are bent towards the multiple axial ▪ bond. Bond angles in heteroligand MXL 5 and MXL′ 4L complexes of similar types are analyzed using vibronic theory of angular distortions in heteroligand molecules. It is shown that the theory permits an explanation of the mentioned anomalous bond angles as well as normal bond angles in related [MNOHal 5] 2− complexes (M = Os, Ru).