Stereoisomers of 3-methylcyclobutene and HBr addition products Steps: - 3-Methylcyclobutene features a chiral center at C3 due to attachment to distinct C2, C4, H, and CH3; the puckered ring yields cis and trans diastereomers. - Each diastereomer lacks symmetry, producing a pair of enantiomers, for 4 total stereoisomers. - HBr adds via electrophilic mechanism: H+ to C1 (less substituted), forming secondary carbocation at C2 (stabilized by adjacent methyl at C3). - Br- attacks planar C2 from either face, creating new chiral center at C2 (attached to C1, C3, Br, H); C3 chirality preserved, yielding 2 chiral centers and 4 stereoisomers (2 diastereomer pairs). Why B is correct: - Two chiral centers in the product (C2, C3) with no meso form due to different substituents and ring asymmetry produce exactly 4 stereoisomers, matching the starting material's 4. Why the others are wrong: - A: Underestimates starting stereoisomers; ignores diastereomers, counting only 2 enantiomers. - C: Overcounts products; assumes both regioisomers (Br at C1 or C2), doubling to 8, but C2 carbocation dominates. - D: Duplicate of C; invalid choice. Final answer: …