# Elimination of HCl from isomeric chlorocyclohexadienes

Which of these is most easily dehydrohalogenated?

a. 5-Chlorocyclohexa-1,3-diene (1)
b. 3-Chlorocyclohexa-1,4-diene (2)
c. 1-Chlorocyclohexa-1,4-diene (3)
d. Both 1 and 3

I encountered this question a while ago. The given answer is option (b) (compound 2). But the dehydrohalogenation of compound 1 produces benzene which has high heat of formation. So why isn't that the answer?

• They both form benzene. Does that change your analysis? – jerepierre Nov 18 '15 at 16:15
• @jerepierre Can you elaborate a bit? – tatan Jun 10 '18 at 7:36
• Can anyone please explain? – PolarBear Jan 25 at 15:53

Assuming that you use a strong base for dehydrohalogenation you will be deprotonating the most acidic $$\ce{H}$$ resulting in formation of a carbanion which has the highest stability in compound number 2