The reaction given in Fig. P17.59 occurs by a mechanism called the S_N2′ mechanism, which is a bimolecular substitution that occurs by reaction of the nucleophile at an allylic carbon. In this reaction, the C—Cl bond as well as the bond to the nucleophile must be perpendicular to the plane of the alkene double bond for proper orbital overlap, but this orientation can occur in two ways: The C—Cl bond can be syn to the new bond that is formed with the nucleophile, or it can be anti. Is the following S_N2′ reaction syn or anti? How does this result contrast with the stereochemistry of the S_N2 reaction?

Transcribed Image Text:

Η Η =C H D -CH3 Cl R isomer Figure P17.59 + E,NH 25-30 °C EtNH HC-C D H C-CH3 H (95%) + EtNH D H C- H C-H CH3 CI (5%)