Correlation between molecular electron affinities and dipole moments

1976 ◽  
Vol 65 (3) ◽  
pp. 1214-1215 ◽  
Author(s):  
K. D. Jordan
Keyword(s):  
Dipole Moments ◽  
Electron Affinities ◽  
Molecular Electron

Molecular structure and relative proton and electron affinities of isomeric nitroimidazoles

1989 ◽  
Vol 67 (10) ◽  
pp. 1666-1671 ◽  
Author(s):  
Salim F. Farah ◽  
Robert A. McClelland ◽  
Michael R. Peterson ◽  
Imre G. Csizmadia
Keyword(s):  
Dipole Moment ◽  
Radical Anion ◽  
Dipole Moments ◽  
Rotational Transition ◽  
Basis Set ◽  
Electron Affinities ◽  
Conjugate Acid ◽  
Biological Effectiveness ◽  
Group Rotation ◽  
Relative Change

The isomeric 2-nitro, 4-nitro, and 5-nitroimidazoles have been studied in their planar ground state, C—NO2 rotational transition state, 3-H protonated conjugate acid and radical anion forms, with abinitio computations at the split-valence 3-21G basis set level. The stabilities of the parent compounds follow the order 5-NO2 ~ 4-NO2 > 2-NO2. In solution 4-nitro is more stable than 5-nitro; the calculations suggest that this is a solvation effect, since the 4-nitro isomer has a considerably higher dipole moment. Barriers for nitro group rotation range from 10 to 16 kcal/mol. However, the relative change in dipole moment during the rotation is small, suggesting that dipole moments of nitroimidazoles are determined mainly by inductive effects, with resonance interactions being relatively unimportant. This conclusion is supported by calculations of molecular electrostatic potentials of the planar and rotated forms. Electron affinities follow the order [Formula: see text], closely matching the order of biological effectiveness of nitroimidazole radiosensitizers. This is consistent with suggestions that the "nitro:nitro radical anion" redox cycle is an important determinant of biological activity. Keywords: nitroimidazole, abinitio computation, rotational barrier, proton affinity, electron affinity.

The evaluation of molecular electron affinities

1986 ◽  
Vol 7 (3) ◽  
pp. 349-358 ◽  
Author(s):  
Jon Baker ◽  
Ross H. Nobes ◽  
Leo Radom
Keyword(s):  
Electron Affinities ◽  
Molecular Electron

MNDO calculations of the molecular and electronic structure of thionitroso, dithionitro and related compounds

1988 ◽  
Vol 53 (9) ◽  
pp. 2116-2127 ◽  
Author(s):  
Achim Mehlhorn
Keyword(s):  
Electron Capture ◽  
Infrared Spectra ◽  
Dipole Moments ◽  
Radical Cations ◽  
Electron Affinities ◽  
Mndo Calculations ◽  
Stabilization Effect ◽  
Related Compounds ◽  
Molecular And Electronic Structure

Compounds with the formulae RNS and RNS2 (thionitroso I and dithionitro compounds II, dithionitrites III, N-thiosulfinylamines IV, dithia-aziridines V and thiazylthiols VI, R = H, CH3, C6H5)and the corresponding radical cations HNS2+ and anions HNS2- have been investigated by MNDO calculations with respect to their molecular geometries, relative stabilities, ionization and electron capture properties and dipole moments. For the simplest representatives (R = H) the infrared spectra have been calculated. The lengths of NS triple (in VI), double (in I, III, IV) and partial double (in II, III) bonds are predicted to be in the region of 147-150, 152-155 and 158-162 pm, respectively. Within these regions systematic shifts result from different substituents R. Contraction of NS bonds (1-6 pm) is observed in the case of ionization whereas electron capture causes bond elongation (2-6 pm). The MNDO sequence of stability deviates from that of ab initio calculations for compounds with tetravalent sulfur the stabilization effect of which is obviously underestimated by the MNDO approach. All compounds studied are characterized by negative non-vertical electron affinities suggesting vigorous reactivity with nucleophilic reactants. The patterns of infrared spectra enable recognition, discrimination and characterization of these mostly unknown compounds which might be accessible as short-living transients.

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