Dibromobutane isomers from diene + 2 HBr and their stereocenters

Steps:

• First HBr addition to buta-1,3-diene yields 3-bromobut-1-ene (1,2-product) and 1-bromobut-2-ene (1,4-product).
• Second HBr to 3-bromobut-1-ene gives 2,3-dibromobutane (CH₃CHBrCHBrCH₃).
• Second HBr to 1-bromobut-2-ene gives 1,2-dibromobutane (BrCH₂CHBrCH₂CH₃) and 1,3-dibromobutane (BrCH₂CH₂CHBrCH₃).
• Chiral centers: C2 in 1,2-dibromobutane (groups: Br, H, CH₂Br, CH₂CH₃); C3 in 1,3-dibromobutane (groups: Br, H, CH₃, CH₂CH₂Br); none in 2,3-dibromobutane due to symmetry.

Why C is correct:

• Two isomers (1,2- and 1,3-dibromobutane) each contain one carbon with four different substituents, per chirality definition.

Why the others are wrong:

• A: Incorrect; two isomers have chiral centers.
• B: Incorrect; both 1,2- and 1,3-dibromobutanes have one each.
• D: Incorrect; 2,3-dibromobutane lacks a chiral center due to molecular symmetry.

Final answer: C