|Class 12 Chemistry Haloalkanes and Haloarenes||Comparison of SN1 SN2 E1 and E2|
Comparison of SN1, SN2, E1 and E2
E2 reaction is favored by strong base whereas strength of base doesn’t determine whether the reaction will be favored or not.
Order of reactivity is same for both the reaction i.e. 3̊ > 2̊ > 1̊ .
E1 reaction is favored by polar protic solvent because it accelerates the reaction by solvating halide ion forming carbonium ion whereas E2 reaction is decelerated by polar protic solvent.
E2 reaction is favored at room temperature whereas E1 reaction requires little higher temperature.
High concentration of a strong nucleophiles or base favors both the reactions.
Increase in temperature favors elimination over substitution. They are entropically favored over substitution due to the fact that products of elimination are greater in number than the reactants and increase in temperature increases the entropy effect. This is due to the relation ΔG0 = ΔH0 – TΔS0.
Another way to influence the elimination reaction is to strong sterically hindered base. In the reaction mentioned below E2 reaction is 85 % whereas SN2 is 15%
Using a strong and slightly polarized base such as amide ion, alkoxide ion influences the elimination reaction.
E1 reactions are favored by the use of substrates that can form stable carbocation. They are also favored by the use of polar solvents. At lower temperature SN1 is favored over E1 reaction.