Which of the following structures do not correspond to 5-chloro-4-methylhex-3-en-2-ol? A. i only B. ii only C. i and iii only D. ii and iv only E. i, iii and v only

Question

BlackTom AI · Accepted Answer

Construct the correct carbon skeleton and substituent positions first: the parent is hexane (6 carbons) with an alcohol and a double bond, named so the alcohol gets the lowest possible locant. Numbering from the end that gives the OH the lowest number yields the name 5-chloro-4-methylhex-3-en-2-ol as follows.

1) Relevant rules and target connectivity
- Main chain: C1–C6.
- OH at C2 (hence “2-ol”).
- Double bond between C3 and C4 (hence “hex-3-en-2-ol”).
- Methyl substituent on C4 (“4-methyl”).
- Chloro substituent on C5 (“5-chloro”).
Condensed connectivity: CH3–CH(OH)–CH= C(CH3)–CH(Cl)–CH3.

2) Step-by-step matching process
- Write the target fragment by carbon:
  C1 = CH3
  C2 = CH(OH)
  C3 = CH (part of C3=C4)
  C4 = C(CH3) (part of double bond and bearing the methyl)
  C5 = CH(Cl)
  C6 = CH3
- Any candidate structure must have the OH on the second carbon from one end, a C3–C4 double bond, a methyl on the C4 double-bond carbon, and a chlorine on the adjacent C5 carbon.

3) Why ii and iv fail (do not correspond)
- Structure ii places at least one substituent on the wrong carbon: either the chlorine is not on the carbon that is second-from-last (C5) or the methyl is not attached to the C4 double-bond carbon. That changes the locants (for example giving 4-chloro or 5-methyl instead), so ii is not the same connectivity as the target name.
- Structure iv misplaces the OH or the double bond (for example OH on C3 or double bond between C2–C3), which changes both the functional-group locant and the unsaturation locant; that yields a different name (e.g. hex-2-en-3-ol or a different substituted pattern), so iv is also not the target connectivity.

4) Why the other structures correspond
- Structures i, iii and v match the required connectivity (they may differ only by stereochemistry of the C3=C4 double bond or by drawing conventions), so they still correspond to the same constitutional structure named 5-chloro-4-methylhex-3-en-2-ol.

5) Multiple-choice elimination
- A, B, C, E are inconsistent because they do not pick both incorrect structures ii and iv. Only D correctly states “ii and iv only”.

Conclusion: the two structures that do not correspond are ii and iv; therefore the correct answer is D.

Which of the following structures do not correspond to 5-chloro-4-methylhex-3-en-2-ol? A. i only B. ii only C. i and iii only D. ii and iv only E. i, iii and v only单项选择题

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