Identify the absolute configuration (R/S) for the chiral centers at positions 2 and 3 in the following Fischer projection: CO_ 2 H at top, H and OH on C2, H and Cl on C3, and CH_ 3 at bottom.

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EEJ MAIN Chemistry QUESTION #7125

Question 1

Identify the absolute configuration ($R/S$) for the chiral centers at positions 2 and 3 in the following Fischer projection: $CO_{2}H$ at top, $H$ and $OH$ on C2, $H$ and $Cl$ on C3, and $CH_{3}$ at bottom.

$(2S, 3R)$✔️
$(2S, 3S)$
$(2R, 3R)$
$(2R, 3S)$

Correct Answer Explanation

At C2: Priority order is $-OH > -COOH > -C(H)(Cl)CH_3 > -H$. The sequence is counter-clockwise, but since $H$ is on the horizontal line, it is 2S.
At C3: Priority order is $-Cl > -CH(OH)COOH > -CH_3 > -H$. The sequence is clockwise, but with $H$ on the horizontal line, it is 3R.

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