[RedsAreRaw]

Sorry this question is long:
"When isobutylene and chlorine are allowed to react in the dark at 0° C in the absence of peroxides, the principal product is not the addition product but methallyl chloride (3-chloro-2-methyl-1-propene). Bubbling oxygen through the reaction mixture produces no change. This reaction was carried out with labeled isobutylene (1-¹⁴C-2-methyl-1-propene, (CH₃)₂C=¹⁴CH₂), and the methallyl chloride contained was collected, purified, and subjected to ozonolysis. Formaldehyde (H₂C=O) and chloroacetone (ClCH₂COCH₃) were obtained; all (97% or more) of the radioactivity was present in the chloroacetone.
(i) Give the structure, including the position of the isotopic label, of the methallyl chloride obtained. (ii) Judging from the evidence, is the reaction ionic or free radical? (iii) Using only steps with which you are already familiar, outline a mechanism that accounts for the formation of this product. (iv) Can you suggest one reason why isobutylene is more prone than 1- or 2-butene to undergo this particular reaction? (v) Under similar conditions, and in the presence of oxygen, 3,3-dimethyl-1-butene yields mostly the addition product, but also a small yield of 4-chloro-2,3-dimethyl-1-butene. In light of your answer to (iii) how do you account for the formation of this minor product?"

Here are my answers, I was wondering if the mechanism and the reasoning were correct. Thanks!

[Dan]

You answers seem fine, but you should justify your answer to (ii) (what would the product(s) of a radical reaction be?) and draw a curly arrow mechanism for (v).

Part (iv) would also benefit from clarification - i.e. what is the nature of the corresponding carbocations in the 1/2-butene reaction and why are they less stable than the one formed in the isobutene reaction.