When acetic acid looses hydrogen, an acetate ion is formed which attacks 4-chlorobut-1-ene, forming methyl butenoate. How does the cyclic structure form? Does the lone pair of oxygen attack the butene moiety internally?
In solvolysis of simple primary cyclopropylmethyl systems the rate is enhanced because of participation by the $\sigma $ bonds of the ring. The ion that forms initially is an unrearranged cyclopropylmethyl cation that is symmetrically stabilized, that is, both the 2,3 and 2,4 $\sigma $ bonds help stabilize the positive charge(page 464 ,JerryMarch ,Advanced Organic Chemistry Reactions, Mechanisms,and Structure,Sixth Edition).
The reaction of various cyclopropylmethyl systems are given below.
In the question 4-chlorobut-1-ene (1) undergoes rearrangement as shown in the scheme 3 and scheme 4 to give 1a, 1b and 1c.Assuming solvolysis with acetic acid ,1a, 1b and 1c would give 2, 3 and 4.