Question

What is the main experimental difference in reaction conditions between substitution and elimination reactions?

Answer 1

General reaction scheme for substitution/elimination:

H-CR''R-CHR''R''''-LG + Nu/B --->H-C-C-Nu (substitution) or -C=C- (elimination)

R,R''',R'',R''''=alkyl group or H

Nu=nucleophile/weak base

B=strong base (mostly negatively charged ones)

For Substitution reaction, 1) the reactant must have a good leaving group like halides Cl-. Br- or bulky stable groups tosyl group -OTs

2) A weak base or nucleophile must react to replace the leaving group.Nucleophiles are generally ,uncharged species with lone pair of electrons

For elimination reactions,1) the reactant must possess an electrophillic center,produced by induction due to the presence of electron withdrawing group in the neighborhood.

2) A strong base must react with the reactant to extract a proton to form an alkene.

3) Increased steric factors tends to lead elimination by the attacking base