(2R,3S)-2,3-Dibromobutane vs (2R,3R)-2,3-Dibromobutane - Isomer Relationship

Introduction

Both molecules are 2,3-dibromobutane with two chiral centers. They have the same connectivity but differ in the arrangement of substituents around C3.

Formula Comparison

Both share the formula C₄H₈Br₂ and have bromine atoms on C2 and C3. The molecular formula is identical.

Connectivity Analysis

The bonding sequence is the same in both: CH₃–CHBr–CHBr–CH₃. Every atom connects to the same neighbors. Since the connectivity is identical, these are not constitutional isomers.

Spatial Relationship

In the (2R,3S) form, the two bromine atoms are on the same side (eclipsed in Newman projection). In the (2R,3R) form, the bromines are on opposite sides (anti). They are not mirror images — only C3 has been inverted, while C2 keeps the R configuration.

Chirality Check

Both C2 and C3 are chiral centers with four different substituents: CH₃, Br, H, and CHBr(CH₃). In the (2R,3S) form, the centers have opposite configurations. In the (2R,3R) form, both centers are R.

Classification

These are diastereomers — stereoisomers that are NOT mirror images. Only one of the two stereocenters is inverted. If both were inverted (R,S vs S,R), they would be enantiomers instead.

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