Diphenyl, resonance structures

In derivatives of diphenyl, owing to the presence of two benzene lings, the number of possible resonance structures is greater than in the case of the corresponding benzene derivatives and the dipole moment is increased. Thus with / -aminodiphenyl ... 

It is well known from chemical history that the discoveries of the first stable organic radicals, such as triphenylmethyl, diphenyl-picrylhydrazyl, tri-tert-butylphenoxyl, and nitroxides are very significant contributions to theoretical chemistry. The relative stabilities of these radicals were attributed by chemists to the participation of an unpaired electron in conjugated ir-electron systems. Classical stable radicals can thus be thought of as a superposition of many resonance structures with different localizations of an unpaired electron. The first stable radical obtained by Pilotti and Schwerin in 1901 in the pure state can be described by a variety of tautomeric and resonance structures as shown in Scheme 1. 

Nuclear magnetic resonance studies on meso-ionic l,2,4-triazol-3-ones (200) were used to examine their relationship to the alternative l,3,4-oxadiazol-2-imine structure (153). The effect of solvent polarity upon the ultraviolet spectrum of anhydro-3-hydroxy-1,4-diphenyl-1,2,4-triazolium hydroxide (200, R = = Ph, R = H) has been discussed... 

The t3C resonances of xanthone (21) have been assigned on the basis of shift analysis of the structurally related compounds anthrone and xanthene (77P735) and by correlation with the component molecules diphenyl ether and benzophenone (78T1837). Delocalization of the non-bonding electron pairs at oxygen, leading to an increase in aromaticity of the pyranone ring, accounts for the deviation of the chemical shifts of C-4a, C-8a and the carbonyl carbon atom from the calculated values. 

Brouwer and Wilbrandt have applied resonance Raman spectroscopy and calculations to questions of structure of amine radical cations [73]. Well-resolved Raman spectra of trialkylamine radical cations that are so short-lived that their electrochemical oxidation waves are irreversible may be obtained at room temperature in solution by photoionization and time-resolved detection. Comparison of the observed spectrum with calculations for various isomers provides a powerful method of answering structural questions. Density-functional calculations prove much easier to apply to open-shell species than Hartree-Fock calculations, which require cumbersome and expensive corrections to introduce suffieient electron correlation to eonsider questions like the charge distribution of disubstituted piperazine (1,4-diazacyclohexane) radical cations. The dimethyl- and diphenyl-substituted piperazine radical cations are delocalized, but charge is localized on one ArN unit of the dianisyl-substituted compound [73dj. 

The first nuclear magnetic resonance (NMR) studies of T3 failed to isolate two distinct spectra for the distal and proximal conformers (8). In addition, molecular orbital (MO) calculations predicted a high barrier to internal rotation about the diphenyl ether bonds (j)). These data suggested that there was only one conformer present in solution, presumably distal, since this was shown to be the active form of the hormone. However, the first crystal structure of T3 showed the 3 -I conformation to be proximal (10), inconsistent with available binding and activity data. 

Diphenyl-4-pyrone (356) has been obtained (35%), along with recovered starting ketone (60%), in the formylation of dibenzylketone (351) with dimethyl-formamide-phosphorylchloride126K As known for other methylene ketones, a double formylation to the chloropentamethinium salt (352) should take place at first, but the sterically overcrowded structure of (352) lacks resonance stabilization and hydro-... 

A combination of N CPMAS NMR, N quadrupole double resonance, and x-ray studies of solid 3,5-dimethylpyrazole (19) between 270 K and 350 K has been necessary to discuss the intermolecular proton transfer in a structure like (55) <89JA7304> the experimental evidence (species HHH and DDD) is consistent with a correlated triple hydrogen jump with an activation energy of 11 kcal mol". The cases of 3,5-diphenyl-4-bromopyrazole (a dimer like (54)) and 3,5-diphenyl-pyrazole (a tetramer like (56)) were subsequently studied <92JA9657> here also proton jumps were found with activation energies similar to those found for (19). The dynamic behavior of pyrazole... 

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