Question

The SN2 Reaction can be described as chemospecicific; define the terms "chemoselectivity" and "chemospecificity", and explain the origin of the observed chemospecifity in the williamson ether synthesis

Answer 1

Chemoselectivity refers to the selective reactivity of one functional group in the presence of others to a certain reactant or the selective preference of a reactant for a certain functional group. But to predict that accurately is difficult because the physical outcome of the actual reaction is ultimately dependent on a number of factors (solvent, atomic orbitals, etc.). A chemoselective reaction gives a major and a minor product, different reactions may occur with different probabilities.

On the other hand, a chemospecific reaction is one where a reaction occurs at only one functional group but not another, for example the oxidation of a primary alcohol but not a secondary alcohol.

The Williamson ether synthesis is an organic reaction forming an ether from an organohalide and analcohol. Typically it involves the reaction of an alkoxide ion with a primary alkyl halide via an S_N2 reaction

The electronegative O- in the alkoxide reacts chemospecifically with the C atom bonded to a very electronegative atome like X, an halogen. Why does this react with that C and not with any other else? It's just a matter of electrostatic forces, that is the carbon more "positive" in the molecule.

This is a very important methos for ethers synthesis when you have a primary alkyl halide, because the high reactivity of alkoxides gives way to elimination reactions with secondary and tertiary alkyl halides.