2. Number the longest chain beginning with the end of the chain nearer the substituent(编号) 654321 765 CH3CH2CH2CH3CHCH3 CH3 CH2 CH2CH3 CHCH3 CH 3 CH 2 CHE Substituent(取代基)2. Number the longest chain beginning with the end of the chain nearer the substituent.(编号） CH3 CH2 CH2 CH3 CHCH3 CH3 CH3 CH2 CH2 CH3 CHCH3 CH2 CH3 6 5 4 3 2 1 7 6 5 4 3 2 1 Substituent （取 代 基 ）