JEE Main levelSingle correct optionDifficulty 2 of 3st015
3-Ethylpenta-1,3-diene, CHX2=CH−C(CHX2CHX3)=CH−CHX3, is drawn with the methyl group on C4 and the ethyl group on C3 on the same side of the C3=C4 double bond. The descriptor for the C3=C4 bond is
AS
BR
CE
DZ
Answer: C
On C3 the vinyl group (C,C,H, with a duplicated carbon) outranks ethyl (C,H,H). On C4 methyl outranks H. The methyl is cis to ethyl, hence trans to vinyl, so the two higher priority groups are on opposite sides: E.