Inert carbon free radicals. 8. Polychlorotriphenylmethyl radicals: synthesis, structure, and spin-density distribution

Abstract

Some symmetrical Ar3C and unsymmetrical (C6C15)3-xAr,C radicals with different chlorine substitution patterns (x = 1, 2; Ar: 2H-C6HC14, 3H,5H-C6H2C14, 4H-C6HC14, C6H5) are prepared. X-ray crystal structures for most of them have been obtained at room temperature. The general conformations are conditioned by the great volume of the chlorine atoms in the ortho positions resulting in unsymmetrical, propellerlike conformations. Experimental evidence of the steric shielding of the trivalent carbon atom, as well as the practical nonexistence of the so-called buttressing effect, is given. The steric shielding is in correlation with the observed stabilities. The magnetic susceptibilities of the radicals are discussed and related to molecular packing and spin densities in terms of McConnell's theory, when antiferromagnetism is observed. The g-factors, hyperfine coupling constants (hcc) of IH and I3C nuclei, and line widths of the radicals are determined at several temperatures by ESR experiments in solid-state and isotropic solutions. Different conformational dynamic behaviors are traced to the number of chlorine atoms in ortho positions. Temperature-dependent line widths are explained by the relative contribution of the modulation of the dipolar hyperfine interaction through molecular tumbling and chlorine nuclear quadrupolar relaxation mechanism. The hcc values have been calculated according to the INDO method with the experimental X-ray geometries and compared with the experimental values; a g o d agreement is obtained. The assignment of the I3C satellites to bridgehead and ortho positions is confirmed IntroductionIn the course of our studies on derivatives of perchlorotri-

(Z)-Perchlorostilbene

“…The C1 substituents are significantly out of the plane of the phenyl ring with C1(7) and C1(4) being most affected. The mean Car--C1 distance of 1.716 (5)A agrees well with the value of 1.722 A calculated for 81 such bonds in the other pentachlorophenyls (Miratvitlles, Molins, Solans, Germain & Declercq, 1985;Pedersen, 1975;Veciana, Carilla, Miratvitlles & Molina, 1987;Armet et al, 1987;Wang, Chen, Xu, Zhang, Pan & Tang, 1987;Gali et al, 1978). (8) The packing diagram for (Z)-perchlorostilbene is shown in Fig.…”

Polychlorinated trityl radicals for dynamic nuclear polarization: the role of chlorine nuclei

“…The gyromagnetic ratio of the electron is 2640 times higher than that of carbon 13 nuclei resulting in a much larger polarization at the same temperature and 20 magnetic field. The high electron polarization can be transferred to nuclei in the bulk of the sample by irradiating at the frequency of electronic spin resonances.…”

“…This is probably due to fast relaxation because of the slow tumbling rate of the molecule in this viscous solvent 10 under the used experimental conditions. 20 The largest observed coupling arise from the phenyl 13 C bridgehead (ipso), followed by the phenyl 13 C in ortho (2,6) with respect to the central carbon atom, followed by the coupling with the phenyl 13 C in para (4) and meta (3,5) positions. Hyperfine 15 couplings were accurately determined by simulation of the experimental spectra.…”

Effect of Cholesterol on Distribution of Stable, Hydrophobic Perchlorotriphenylmethyl Triethylester Radical Incorporated in Lecithin Liposomal Membranes

“…The derivatives of triarylmethyl radicals including perchlorotriphenylmethyl radicals were reported to be bulky and propeller-shaped. [28][29][30] PTM-TE with such a bulky structure may be excluded from membranes to form PTM-TE clusters.…”