Resonance Energy Calculation: the MMZERW Force Field*The additivity of the thermochemical conjugation energy in acyclic systems allows one to extend force-field calculations to conjugated n systems without embarking on quantum-mechanical methods. The approach fails with cyclic delocalized systems, where resonance effects become important. Here the method provides the reference value needed to calculate resonance energies.
Inversion Barriers of ortho,ortho'-Bridged BiphenylsThe syntheses and spectroscopic properties of the ortho,ortho'-bridged biphenyls 2-19 are described. In the case of 5, 15, and 16 the inversion barrier is determined from the temperature dependence of the NMR spectra (lineshape analysis), in the case of 12,13, and 14 from the temperature of coalescence, and in the case of 2a. 3b, 7. l?, 18, and 19 from the rate of racemization of the optically active compounds. The experimental inversion barriers, including data from the literature, are compared with those calculated using the extended force field (MM2erw). The conformational behavior of the title systems is significantly affected upon transformation into the corresponding dianion salts. The relevant energy terms are discussed.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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