Biphenyl Optical activity

The products 4 are formed as racemic mixtures, but can be resolved by recrystallization of diastereomeric salts.23 - 25 Syntheses starting from optically active biphenyl compounds are also known.26 -28 l,l -Binaphthyl-2,2 -diamine(5) can be transformed to the dinaphtho[1,4]di-azocine 6 by melting with benzil.29... 

The molecules most profitably studied in connection with purely steric isotope effects have been isotopically substituted biphenyl derivatives. Mislow et al. (1964) reported the first more or less clearcut example of this kind in the isotope effect in the configurational inversion of optically active 9,10-dihydro-4,5-dimethylphenanthrene (7), for which an isotopic rate ratio ( d/ h) of 1-17 at 295-2°K in benzene solution was determined. The detailed conformation of the transition state is not certain in this case, as it involves the mutual passage of two methyl groups, and thus it is difficult to compare the experimental results with... 

Westheimer FH, Mayer JE. The theory of the racemization of optically active derivatives of biphenyl. J Chem Phys 1946 14 733-8. 

Kaiser KLE (1974) On the optical activity of polychlorinated biphenyls. Environ Pollut 1 93-101. 

R)- and (S)-(6,6 -Dimethylbiphenyl-2,2 -diyl)bis(diphenylphosphine), BIPHEMP (1). This is the first example of an optically active bis(triarylphosphine) containing the axially disymmetric biphenyl group. The 6,6 -dimethyl groups are used to... 

As already reported in Sects. IV-C and V, there are a few examples of chiral polymers not containing classical asyrrunetric carbon atoms or odier elements of localized chirality (substituted biphenyls, etc.). In such cases chirality is related to the presence of rigid helical conformations and optical activity derives from an excess of chain segments turned in one or the other sense. We may distinguish polymers in which conformational rigidity (and hence the possibility... 

From the NMR-data for dl 33 and meso 33 it can be concluded that in the racemic form both hexahelicenyl moieties are almost perpendicular, whereas in the mesoform the central biphenyl moiety is planar 25). The three double helicenes 54, 55 and 56 could only be isolated in one form. For 55 this was the racemic form having the terminal rings at opposite sides of the central part, as could be deduced from the isolation of optically active samples. From racemization experiments (vide infra) it could be deduced that the mesoform can hardly exist. Comparison of the NMR spectra of 54 and 56 with that of 55 suggests that 54 and 56 are also racemic forms. The chemical shift of H(16) and H(17) in 56 has the lowest value found for protons in carbohelicenes. 

Considerable interest has been shown in dibenz[c,e]azepines as examples of optically active 2,2-bridged biphenyls (68MI51600). The absolute configurations of some dibenz[c,e]azepines have been determined (b-77SH(2)305), and the CD spectra of the hydro-2-benzazepin-l-one (22) recorded (78CHE538). In contrast, to analogous five- and six-membered lactams, azepinone (22) has a (+) Cotton effect. 

Berson, J. A., and M. A. Greenbaum Asymmetric induction studies with optically active biphenyls. V. On the unreliability of absolute configurational assignments based on hydride reductions ofphenylglyoxylatcs. J. Amer. chem. Soc. 81, 6456 (1959). 

The effect of steric hindrance in giving rise to optical activity of o,o -substituted biphenyls is well known.87... 

In Zimmerman s picture of n,ir triplets of dienones undergoing skeletal rearrangements, the second double bond is essential. However, Chapman s idea of the excited state adapts itself readily to explaining the behavior of the enones. Both authors have now examined the behavior of ketone 35. Chapman finds that irradiation of an optically active sample of 35 yields a product which is almost 100% optically active.415 Zimmerman finds that the reaction can be quenched very efficiently by both naphthalene (ET = 61 kcal) and di-te/7-butylni-troxide, but only weakly by biphenyl (ET 70 kcal).416... 

Optically active biphenyl derivatives (Section 13-5 A) are racemized if the two aromatic rings at any time pass through a coplanar configuration by rotation about the central bond. This can be brought about more or less easily by heat, unless the 2,2 -ortho substituents are very large. 

Besides BINAP or p-TolBINAP, optically active peraryldiphosphines with axial chirality based on the biphenyl groups (6,6 -dimethylbiphenyl-2,2 -diyl)bis(diphenylphosphine) and its analog are also effective ligands for the asymmetric isomerization as expected [21],... 

In spite of the uncertainty in the equilibrium conformation of biphenyl in the liquid phase, it is reasonable to anticipate an energy barrier to free rotation and coplanarity. Adoption of the highly successful Westheimer-Mayer model (Westheimer, 1956) for the racemization of optically active biphenyls leads to a calculated value of 3.9 kcal mole-1 for the barrier to free rotation (Howlett, 1960). The calculation was made on the basis of a large stabilization energy, 7 kcal mole-1, for the coplanar molecule (Guy, 1949). 

Among the different types of compounds whose complexation properties have been studied are various amides linear oxoamide 9 [22], fumaramide 10 [23,24] and methanetricarboxamide 11 [25], biphenyl derivatives 12 [26], and derivatives of tartaric acid 13-16, that can also be prepared in an optically active form [27], The above-mentioned chiral hosts have been found to form inclusion complexes with chiral guests 17 and 18. Molecular recognition between chiral hosts and... 

Sanfilippo, C. Nicolosi, G. Delogu, G. Fabbri, D. Dettori, M. A. Access to optically active 2,2 -dihydroxy-6,6 -dimethoxy-l,l -biphenyl by a simple biocatalytic procedure. Tetrahedron Asymmetry 2003, 14, 3267-3270. 

Optical activity can also be induced on achiral azobenzene units when they are incorporated into the polymer main chains through covalent bonding to chiral subunits (34-37 in Fig. 14) [88-92]. Axially chiral amino- or carboxy-substituted biphenyl and binaphthyl and tartaric acid derivatives were used as the optically... 

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