Abstract
Abstract Conformational energy calculations on 2,4-dimethyl-2,4-diphenylpentane have been performed with explicit allowance for methylene bond-angle flexibility. The value of this angle which minimizes the energy is close to 126°, whatever the conformation. The energy contours are given versus main chain bond rotations. An intramolecular mobility study reveals that two kinds of motions are expected: the first includes motions with low activation energies while motions of the second group require a much higher activation energy and involve a large rotation around C-C skeleton bonds. In all cases the phenyl ring rotations are rather strongly coupled with the chain rotations. IR analysis and intramolecular excimer formation indicate that 2,4-dimethyl-2,4-diphenylpentane exists in one of the most stable conformations in the crystalline state. In the liquid state higher-energy conformers are present. Fluorescence emission studies show that 2,4-dimethyl-2,4-diphenylpentane exhibits a higher efficiency of excimer formation than 2,4-diphenylpentane, because of the rather small energy barrier between the excimer and the ground-state conformations.
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