6,6 -Dinitro-2,2 -diphenic acid

Reduction. The reagent is useful for reduction of carboxylic acid esters to primary alcohols. For example, the following esters have been reduced to the corresponding carbinols ethyl p-nitrobenzoate (96% yield), ethyl phenylacetate (90% yield), ethyl gly-cinate (70% yield). The reaction has some useful features Hydroxylic solvents (ethanol, water) can be used, the selectivity is higher than in the case of lithium aluminum hydride, and the reagent is nearly neutral. The reagent was found to be satisfactory for reduction of the dimethyl ester of 4,4 -dinitro-2,2 -diphenic acid (la) to the corresponding alcohol (lb, 51%yield).2... 

A case in point which does not involve a metal complex (excluding for purposes of discussion the proton as a pseudo metal ion) is the Kuhn effect. The late R. Kuhn and Albrecht showed that the quinine salt of 4,4 -dinitro-diphenic acid is dextro rotatory in chloroform. The quinine salts of two... 

Dinitro-6,6 -diphenic acid can actually be resolved into two enantiomeric forms, but heating the samples causes them to racemize. Explain. 

G. H. Christie and J. Kenner, J. Chem. Soc., 71, 614 (1922). Molecular Configurations of Polynuclear Aromatic Compounds. I. The Resolution of Y-6,6 -Dinitro- and 4,6,4, 6 -Tetranitro Diphenic Acids into Optically Active Components. 

In the acid fractionation of the low-boiling portion, b.p. 120-140yi mm., of crude nicotine, the third fraction contains optically impure Z-anatabine which is purified by crystallization of the perchlorate. The mother liquor from the perchlorate (403) contains an optically inactive base which on dehydration produces 3, 2-dipyridyl, while oxidation of its benzoyl derivative gives rise to hippuric acid. Since the base has been resolved with Z-6,6 -dinitro-2,2 -diphenic acid to Z-anatabine it is dZ-anatabine. 

As it can be seen, lUPAC definition covers more situations than the present review that is restricted to biphenyl heterocyclic analogues. Natta and Farina (72M11) offer an interesting discussion on this subject (they used the term atropisomerism, also found in the old references). In the authoritative book by Eliel et al. (94MI1), Chapter 14-5 is devoted to biphenyls atropisomerism. They report that this type of enantiomerism was discovered by Christie and Kenner in 1922 (22JCS614) in the case of 6,6 -dinitro-2,2 -diphenic acid (1) that they were able to resolve. It was later called (33MI1) atropisomerism. An important aspect of all the concepts related to a barrier is (we quote) It is immediately obvious that the term suffers from all the problems discussed previously How slow must be the interconversion of the enantiomers (i.e., how long is their half-life) before one speaks of atropisomerism At what temperature is the measurement to be made Does atropisomerism still exists when isolation of stereoisomers becomes difficult or impossible but their existence can be revealed by NMR (or other spectral) study and so on. ... 

Further studies on the effect of chiral elements showed that ketone 10 derived from 6,6 -dinitro-2,2 -diphenic acid gave ee values similar to ketone 9 (Scheme 3.10)... 

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