CH.CH-CHCH.CH 2-戊烯 CH3 CH2-CH3 CH3-CH-CH2-C-CH2 5 4 3 2 4-甲基-2-乙基-1-戊烯 1 2 3 4 5 CH3 CH=CHCH2 CH3 2-戊烯 CH3 CH CH2 C CH2 CH3 CH2 CH3 5 4 3 2 1 4-甲基-2-乙基-1-戊烯