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Free radical geometry

G. Herzberg (Ottawa) contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals. [Pg.1298]

What is the preferred geometry about the radical center in free radicals Carbocation centers are characterized by a vacant orbital and are known to be planar, while carbanion centers incorporate a nonbonded electron pair and are typically pyramidal (see Chapter 1, Problem 9). [Pg.236]

Free radical and excited ion formation Bond scission/cross-linking Cosmetic effects Drug/polymer reactions Effects vary with geometry/additives... [Pg.594]

O Malley, P., and S. J. Collins. 1996. Density functional studies of free radicals accurate geometry and hyperfine coupling prediction for semiquinone anions. Chem. Phys. Lett. 259, 296. [Pg.123]

Perhaps the most fruitful of these studies was the radiolysis of HCo(C0)4 in a Kr matrix (61,62). Free radicals detected in the irradiated material corresponded to processes of H-Co fission, electron capture, H-atom additions and clustering. Initial examination at 77 K or lower temperatures revealed the presence of two radicals, Co(C0)4 and HCo(C0)4 , having similar geometries (IV and V) and electronic structures. Both have practically all of the unpaired spin-density confined to nuclei located on the three-fold axis, in Co 3dz2, C 2s or H Is orbitals. Under certain conditions, a radical product of hydrogen-atom addition, H2Co(C0)3, was observed this species is believed to have a distorted trigonal bipyramidal structure in which the H-atoms occupy apical positions. [Pg.187]

The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic or microsomal reduction of several potential antiprotozoal 1,2,5-oxadiazoles were characterized and analyzed. Ab initio MO calculations were performed to obtain the optimized geometries, and the theoretical hyperfine constant was carried out using Zerner s intermediate neglect of differential overlap (ZINDO) semi-empirical methodology. DFT was used to rationalize the reduction potentials of these compounds <2003SAA69>. [Pg.318]

In general, it is considered very unlikely that free radicals exist as non-classical structures (Walton, 1987). Kinetic and product studies involving the 2-norbornyl radical revealed the lack of importance of the non-classical species (Bartlett and Pincock, 1962 Martin and De Jongh, 1962 Bartlett and McBride, 1965). More recent ESR studies on the systems [150] and [151], in which the geometry was considered favourable for homoconjugation, again demonstrated the ineffectiveness of non-classical structures for radicals (Walton, 1987). [Pg.316]

Free radical addition of HBr to buta-1,2-diene (lb) affords dibromides exo-6b, (E)-6b and (Z)-6b, which consistently originate from Br addition to the central allene carbon atom [37]. The fact that the internal olefins (E)-6b and (Z)-6b dominate among the reaction products points to a thermodynamic control of the termination step (see below). The geometry of the major product (Z)-(6b) has been correlated with that of the preferred structure of intermediate 7b. The latter, in turn, has been deduced from an investigation of the configurational stability of the (Z)-methylallyl radical (Z)-8, which isomerizes with a rate constant of kiso=102s 1 (-130 °C) to the less strained E-stereoisomer (fc)-8 (Scheme 11.4) [38]. [Pg.706]

Gerhard Herzberg Canada, b. Germany structure and geometry of free radicals... [Pg.410]

Calculated geometries for a small number of diatomic and small polyatomic free radicals are compared with experimental structures in Table 5-18. These have been drawn from a somewhat larger collection provided in Appendix A5 (Tables A5-50 to A5-57). Except for triplet oxygen, all radicals possess a single unpaired electron (they are doublets). The usual set of theoretical models has been examined. All calculations involve use of the unrestricted open-shell SCF approach, where electrons of different spin occupy different orbitals, as opposed to the restricted open-shell SCF approach, where paired electrons are confined to the same orbital (see Chapter 2 for more detailed discussion). [Pg.172]


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See also in sourсe #XX -- [ Pg.275 ]




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Radicals geometry

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