Alkene Nomenclature 4 2 5 CH,=CH一CH2一CH CH2=CH一CH2一CH2一CH IUPAC names: I-butene I-pentene new IUPAC names: but-1-ene pent-1-ene cyclohexene 2 3 4 2 4 CH,一CH=CH一CH CH一CH=CH一CH2一CH IUPAC names: 2-butene 2-pentene new IUPAC names: but-2-ene pent-2-eneAlkene Nomenclature