A student Al Lillich has prepared a pure sample of 3-bromo-l-butene (A). Several weeks later he finds that the sample is contaminated with an isomer B formed by allylic rearrangement.
(a) Give the structure of B.
(b) Give a curved-arrow mechanism for the formation of B from A.
(c) Which should be the major isomer at equilibrium, A or B? Explain.