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Cis/trans isomers; structure of 2-chloro-3-methyl... [partly illegible]

Short answer

Cis-trans isomers require a double bond with each carbon bearing two different groups. 2-Chloro-3-methylpent-2-ene (CH3–C(Cl)=C(CH3)–CH2CH3) shows geometrical isomerism. CIP priorities: Cl > CH3, C2H5 > CH3; the isomer with Cl and C2H5 on the same side is Z, on opposite sides is E.

What are cis and trans isomers? Explain the condition req[uired ?] ... examples. Draw the structure of 2-chloro-3-methyl p[?] ... configuration.

Reading: the question is cut off. I read it as "What are cis and trans isomers? Explain the condition required for them, with examples. Draw the structure of 2-chloro-3-methylpent-2-ene and give its Z/E configuration."

Cis and trans isomers

Geometrical isomers in which similar groups lie on the same side (cis) or opposite sides (trans) of a C=C bond. Example: cis- and trans-but-2-ene; maleic (cis) and fumaric (trans) acids.

Condition

Rotation about C=C must be restricted (a π bond), and each doubly bonded carbon must carry two different groups. For example, 2-methylpropene (CH₃)₂C=CH₂ shows no cis–trans isomerism since one carbon has two identical groups.

2-Chloro-3-methylpent-2-ene, CH₃–C(Cl)=C(CH₃)–CH₂CH₃

C2 carries Cl and CH₃; C3 carries CH₃ and C₂H₅. So geometrical isomers exist.

   Cl      C₂H₅               Cl      CH₃
     \    /                     \    /
      C==C                        C==C
     /    \                     /    \
  CH₃      CH₃                CH₃      C₂H₅
     (Z)                          (E)

Priorities: at C2, Cl > CH₃; at C3, C₂H₅ > CH₃. Cl and C₂H₅ on the same side is Z; on opposite sides is E.

✓ Answer checked by Claude Opus 5.5 (high effort)

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