Relations between Intra- and Intermolecular Steric Effects

Relations between Intra- and Intermolecular Steric Effects 

In Section II, devoted to intermolecular processes, it appeared that most of the quantitative analysis of steric effects was made using a single parameter approach. However, analysis has shown that a correct description of the size of a substituent rests on its preferred conformational states, which are related to the interactions with both the planar heteroaromatic ring to which it is bonded and neighboring groups. This was the topic of Section III. 

Section IV correlates intramolecular and intermolecular steric effects where it is important to consider the ease of strain energy minimization in the order rotation bending streching, and also the three major structural situations discussed below in Sections IVA-C. 

When R2 is spherical with Cx symmetry, the preferred mode of energy minimization will be bond bending as in the hindered rotation of biphenyls. 

This is clearly exemplified by the respective S° values of R2 groups such as phenyl (—1.82), 2-tolyl (—0.77), 1-naphthyl (—0.75), mesityl (—0.23), and 2-pyridyl (-2.35) and 2-thienyl (-2.46) (80JCS(P2)1350). 

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IV. Relations between Intra- and Intermolecular Steric Effects.272... 

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