NOTE :-
#E_2# reaction is Anti-elimination reaction so see in the picture given below :-
#1)# in first case the reaction will occur because the adjacent #Cl# and #H# atoms are Anti, so elimination is possible.
#2)# in the second case the reaction will not occur because the adjacent #Cl# and #H# atoms are Syn so elimination is not possible there in second case.
The reaction of Alkyl halide #(RX)# with Strong base like alc. #KOH# in the presence of heat is Elimination reaction and it follows the #E_2# mechanism and this reaction gives Alkene as the final product along with the corresponding Hydrogen halide #(HX)#.
General #E_2# reaction in the Presence of Heat :-
#RX + alc KOH rarr #Alkene #+ HX#
