# Can't decide between E1 and E2 mechanisms for this reaction

I can see that due to the substrate being bulky, an elimination reaction will take place and not substitution. The reagent is a strong base. E1 reactions are independent of the base chosen, and E2 requires strong base. There is no information about the geometry of the substrate (i.e., whether the beta hydrogens are anti to the halide). How do I decide between the two mechanisms?

• I’m not sure that the E1/E2 question is as important for answering what the major product is. Just think about which hydrogen is most acidic. – ringo Dec 22 '18 at 8:09
• Oh, I get it now. It is the beta hydrogen attached to the benzylic carbon. Since its removal would form a stable carbocation, that is where the elimination would take place, right? – Ritwik Ojha Dec 22 '18 at 8:51
• And now, since the reaction does depend on the stability of carbocations, can I say it proceeds through E1? Or is there still no conclusion to be drawn about that? – Ritwik Ojha Dec 22 '18 at 8:52
• What do you mean about the geometry of the substrate? – Karl Dec 22 '18 at 12:40
• That was about the anti geometry required between the beta hydrogen and the halide, in order for E2 to take place. – Ritwik Ojha Dec 22 '18 at 12:42

You have a tertiary halide. These dissociate rather easily into the relatively stable tertiary carbocation and the free anion. That in and by itself should be indication enough that the reaction proceeds via E1. Alcoholates are only moderately strong bases so the mechanism cannot be $$\mathrm{E1_{cb}}$$.
Once you have the tertiary carbocation, any of the β hydrogens could dissociate. You would likely initially get some kind of mixture based on the corresponding $$\mathrm pK_\mathrm a$$ values weighted by the number of hydrogens. Looking at the three different carbons, one is obviously much more acidic because it is benzylic. This explains the major product.