Bond Angle Parameters Research Articles

On the estimation of second moment for organic compounds in wide-line pmr: analysis of group geometry

Neutron diffraction data available in the literature have been analyzed statistically to arrive at the ideal geometry for the commonly occurring groups, NH 4 + , NH 3 + , CH3, CH2, and CH; this has yielded optimum experimental values for the bond length and bond angle parameters. They are: N-H distance of 1.030 A in both NH 4 + and NH 3 + groups, H-N-H angle of 109.47° and 108.1° respectively in NH 4 + and NH 3 + and 110.8° for the corresponding X-N-H angle in −NH 3 + . For CH3, CH2, and CH groups the bond length C-H is 1.090 A, while the H-C-H and X-C-H angles are respectively 108.2° and 110.5° in CH3 and 107.2° and 109.3° in CH2. The importance of using precise values of both bond lengths and bond angles for the ideal geometry when estimating theoretical second moments is emphasized.

Hydrazinelike Defect, N2H4+, in Irradiated Ammonium Halides. II. Theoretical Analysis

An LCAO–MO energy level diagram and bond length estimates are used to describe a planar ethylenic molecule model for the N2H4+ defect at an NH4+ site in ammonium halides. The unpaired spin orbital is found to be an antibonding combination of 2p orbitals on each nitrogen perpendicular to the molecular plane. The model is then further specified and used to analyze the low-temperature EPR data for NH4Cl in detail, from which hyperfine, bond length, and bond angle parameters are extracted and compared with LCAO–MO calculations. Thereby, more information about the defect and confirmation of the model are obtained. Satellite intensity and linewidth angular variations in the high-temperature spectra are explained, and the relation of high- to low-temperature spectra is discussed.