Stereochemistry of addition reactions

A number of groups have criticized the ideas of Dauben and Noyce, especially the concept of PDC. Kamernitzsky and Akhrem, " in a thorough survey of the stereochemistry of addition reactions to carbonyl groups, accepted the existence of SAC but not of PDC. They point out that the reactions involve low energies of activation (10-13 kcal/mole) and suggest that differences in stereochemistry involve differences in entropies of activation. The effect favoring the equatorial alcohols is attributed to an electrostatic or polar factor (see also ref. 189) which may be determined by a difference in the electrostatic fields on the upper and lower sides of the carbonyl double bond, connected, for example, with the uncompensated dipole moments of the C—H bonds. The way this polar effect is supposed to influence the attack of the hydride is not made clear. 

We are almost ready to begin learning the actual reactions. But first, we must explore one more subtlety associated with the stereochemistry of addition reactions. Consider the following example ... 

The stereochemistry of addition reactions of Br2 to olefins is difficult to control. For example, the reaction of ( )-stilbene (1) with Br2 in CH2CI2 gives a 84 16 mixture of meso- (2) and rac-l,2-dibromo-l,2-diphenylethane (3) in 98%... 

Stereochemistry of addition reactions involving allylsilanes 23.4.12 Intermolecular additions to aldehydes, ketones and acetals... 

The Arrangement of Atoms in Space The Stereochemistry of Addition Reactions... 

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