Benzenes, substituted, condensed-phase

There is no experimental evidence for 7r-complexation of arenes to gold centers in the condensed phase. Quantum-chemical calculations were carried out on various levels of theory for 1 1 and 2 1 complexes of benzene and substituted benzenes with Au+ in the gas phase. For all model systems investigated, it has been predicted that an -coordination to a single carbon atom is the ground state of the cation (Cy-symmetry for [(C6H6)Au]+ and 6 -symmetry for [(C6H6)2Au] ). Similar results were obtained for hexafluorobenzene, for which a coordina-... 

A remarkable series of papers has appeared over the last few years reporting the photoisomerization of substituted benzenes, largely in the condensed phase. One of the earliest observations of photoisomerization in benzenes was that of Van Tamelen and Pappas38 who irradiated an ether solution of 1,2,4-tri-I-butyl benzene (1) with a Hanovia Type L lamp and identified a product as the Dewar analog of tributyl benzene (2). This compound reverted thermally to the starting material... 

Benzoin condensation.1 The benzoates of cyanohydrins of aromatic aldehydes undergo benzoin condensation with an aromatic aldehyde in 50% NaOH/C6H6 in the presence of a phase-transfer catalyst, benzyltriethylammonium chloride. Theoretically two symmetrical and two unsymmetrical benzoins are possible, but in practice only one unsymmetrical benzoin is formed, that in which the carbonyl group is adjacent to the benzene ring substituted by the more electron-donating group. 

E. L. Mackor et al., Trans. Faraday Soc. 54, 66, 186 (1958), have measured for both substituted and condensed aromatics in liquid HF-BFa mixtures by using phase partition to obtain data. II0 in HF-NaBF4 at 0°C is about —8.6, so the system is surprisingly acidic. Their pKj values range from 6.3 for toluene to —1.4 for hexamethyl-benzene and —6.4 for 9,10-dimethyl anthracene. I his last is evidently a reasonably strong base in HF. 

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