An acyclic alkene X with molecular formula C₇H₁₄ yields acetone as one of its products upon reductive ozonolysis. When X reacts with HBr in the presence of peroxides, it forms a halogenated product Y that exhibits exactly 4 stereoisomers. The number of allylic hydrogen atoms ( -hydrogens) in the major alkene X is ________.

Step-by-step solution

Acetone from the reductive ozonolysis of X indicates the presence of a (CH₃)₂C= group. Given the molecular formula C₇H₁₄ , the remaining fragment of the alkene must be =CH-C₄H₉ . Thus, the structure of X is (CH₃)₂C=CH-C₄H₉ . Reaction of X with HBr in the presence of peroxides proceeds via an anti-Markovnikov free radical addition. The bromine radical adds to the less substituted carbon (the CH carbon) to generate the more stable tertiary radical, which then abstracts a hydrogen atom. The product Y is (CH₃)₂CH-CH(Br