2. Obviously, this topic is to study isomers of unsaturated hydrocarbons. Because 3- methylpentane is produced, the position of double bond is inferred from this result. Because A has cis-trans isomerism, it means that the groups on both sides are different. After deducting A, look at the addition of HBr, then subtract HBr to get C, and finally the remaining isomer is B. The result should be li 1lulu:
A: 3- methyl -2- pentene
B:3- methyl-1- pentene
C:2- ethyl-1- butene
D:3- methyl -3- bromopentane
You can verify it.