The compound phenylbenzene (C6H5 -C6H5) is called biphenyl, and the ring carbons are numbered in the following manner:

Use models to answer the following questions about substituted biphenyls.
(a) When certain large groups occupy three or four of the ortho positions (e.g., 2, 6, 29, and 69), the substituted biphenyl may exist in enantiomeric forms. An example of a biphenyl that exists in enantiomeric forms is the compound in which the following substituents are present: 2-NO2, 6-CO2H, 2(-NO2, 6(-CO2H. What factors account for this?
(b) Would you expect a biphenyl with 2-Br, 6-CO2H, 2(-CO2H, 6(-H to exist in enantiomeric forms?
(c) The biphenyl with 2-NO2, 6-NO2, 2(-CO2H, 6(-Br cannot be resolved into enantiomeric forms. Explain.

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3 2 2 3 6 5