Compound 3.42: This compound is an allene. The absence of rotation around the C=C=C axis of an allene is due to electronic rather than steric effects, so this compound will not undergo thermal racemization.
Compound 3.43: This compound is an allene. The absence of rotation
around the C=C=C axis of an allene is due to electronic rather than steric
effects, so this compound will not undergo thermal racemization.
Compound 3.45 This compound is an exo-alkylidene monocyclic
compound. The absence of rotation around the C=C axis of an alkene is due
to electronic rather than steric effects, so this compound will not undergo
thermal racemization.
Compound 3.46 This compound is a bicyclic compound. The two enantiomers cannot be interconverted except by the breaking of at least one carbon-carbon bond, so this compound will not undergo thermal racemization.
Compounds 3.51 and 3.52 These two compounds are biphenyls. The two enantiomers of these compounds can interconvert by rotation around the carbon-carbon bond between the two aromatic rings, a process which is prevented only by steric effects (cf. Figure 3.10 and the associated text). Hence, these two compounds will undergo thermal racemization.
Compounds 3.55 and 3.56 These two organometallic compounds contain a plane of symmetry caused by the two substituents attached to the aromatic ring. The interconversion of the two enantiomers of these compounds requires the breaking of at least one chemical bond, so the compounds will not undergo thermal racemization.
Compounds 3.57-3.59 These three compounds contain a plane of symmetry. For each of these three compounds, the two enantiomers can be interconverted by rotation around the carbon-carbon bonds attached to the ring or alkene at the bottom of the structures. This process is prevented only by steric effects, so the compounds will undergo thermal racemization.
Compounds 3.61-3.64 These four compounds are all helical. In each case, the two enantiomers of the compound can be interconverted by rotation around single bonds, or (in the case of 3.60) by stretching chemical bonds to allow the front of the molecule to pass to the rear. These processes are prevented only by steric effects, so the compounds will undergo thermal racemization.
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