Discussion
Consider the E1 reaction of tert-amyl halides from the energy profile given below.
Identify product P1 and its yield relative to P2
Answer: D
P1 is M and is the minor product.
The common carbocation loses a proton in two ways: from the CH3 group to give M, 2-methylbut-1-ene (a disubstituted, terminal alkene), or from the CH2 group to give N, 2-methylbut-2-ene (a trisubstituted alkene). The more substituted alkene N is more stable (Zaitsev's rule), so it is the lower-energy product, P2, and the less stable M is P1.
The plot also shows a higher barrier from the cation to P1 than to P2. P1 is therefore formed more slowly and is the less stable product: by either measure it is the minor one.
Calling P1 N reverses the stabilities, and calling P1 the major product ignores both its higher barrier and its higher energy.
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