Among the following compounds, the number of compounds that DO NOT exhibit optical activity at room… · ABC26OR0767
Subject: Organic Chemistry · Chapter: Stereochemistry · Topic: Stereochemistry – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Medium
Among the following compounds, the number of compounds that DO NOT exhibit optical activity at room temperature is ____ . 
Answer
Answer (as printed): 4
The options are missing from the source scan for this question, so there is nothing here for this letter to point at. The letter is what the book printed.
Explanation
Answer: 4 — Not optically active: (i) the cumulene H₃COOC–CH=C=C=CH–COOCH₃ (three cumulated C=C, so the ends are coplanar; cis/trans isomerism only, achiral); (ii) the tartaric acid as drawn is (2R,3S), i.e. meso; (iii) the biphenyl with ortho F, F, OCH₃ and H, where the small fluorines let the rings rotate at room temperature, so it racemises; (iv) the [2.2]paracyclophane with both Br on one deck flanking the same bridgehead, which is achiral because the mirror plane through the two bridges maps one Br onto the other. Optically active: PhC(CH₃)(H)OCH₃ and (R)-2-methylcyclohexanone.
Study loop for Stereochemistry