CHE2613 Assignment 2 Solutions 2026
UNISA
Organic Chemistry II: Stereochemistry, Mechanisms, Aromaticity
, Question 1 — Stereochemistry & Mechanisms
1.1 CIP Configuration Assignment
Instructions: Apply CIP sequence rules: assign priorities 1–4 to substituents by atomic
number. Arrange so priority 4 is pointing away; if 1→2→3 is clockwise = R, counter-
clockwise = S.
(a) Five-membered lactone with HO, H, CH₃ substituents
Analysis: The stereocenter (marked *) has substituents: HO (1), O-ring (2), CH₃ (3), H (4).
Priority assignment: O of OH (atomic no. 8) > O of ring > C of CH₃ > H
With H pointing away (dash): the sequence HO→O-ring→CH₃ traces
Configuration (a): (S) — counter-clockwise arrangement of priorities 1→2→3
(b) Cyclopentenone with OH and vinyl/Ph substituents
Stereocenter at C-1 (the ring carbon bearing H and OH):
Substituents on C1: OH (1st priority, O), ring C going to C=O (2nd), ring C going to C=C
(3rd), H (4th)
C-1 configuration: With H on dash (pointing back), check orientation:
C-1: (R) configuration
Note: The second stereocenter at C-5 (bearing H and OH): apply same method
C-5: (S) configuration — Overall: (1R,5S)
UNISA
Organic Chemistry II: Stereochemistry, Mechanisms, Aromaticity
, Question 1 — Stereochemistry & Mechanisms
1.1 CIP Configuration Assignment
Instructions: Apply CIP sequence rules: assign priorities 1–4 to substituents by atomic
number. Arrange so priority 4 is pointing away; if 1→2→3 is clockwise = R, counter-
clockwise = S.
(a) Five-membered lactone with HO, H, CH₃ substituents
Analysis: The stereocenter (marked *) has substituents: HO (1), O-ring (2), CH₃ (3), H (4).
Priority assignment: O of OH (atomic no. 8) > O of ring > C of CH₃ > H
With H pointing away (dash): the sequence HO→O-ring→CH₃ traces
Configuration (a): (S) — counter-clockwise arrangement of priorities 1→2→3
(b) Cyclopentenone with OH and vinyl/Ph substituents
Stereocenter at C-1 (the ring carbon bearing H and OH):
Substituents on C1: OH (1st priority, O), ring C going to C=O (2nd), ring C going to C=C
(3rd), H (4th)
C-1 configuration: With H on dash (pointing back), check orientation:
C-1: (R) configuration
Note: The second stereocenter at C-5 (bearing H and OH): apply same method
C-5: (S) configuration — Overall: (1R,5S)
