See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

**Bromination of trans-2-butene:** **Step 1: Structure of trans-2-butene** $$CH_3-CH=CH-CH_3 \text{ (with trans configuration)}$$ **Step 2: Mechanism of bromination** Bromine adds to the alkene via an anti addition mechanism through a cyclic bromonium ion intermediate. The two bromine atoms add to opposite faces of the double bond. **Step 3: Identify the stereogenic centers** After bromination: $CH_3-CHBr-CHBr-CH_3$ This product has **two stereogenic centers** (the two carbons bearing bromine). **Step 4: Stereochemical outcome** - The anti addition mechanism ensures the two $Br$ atoms add from opposite faces - This creates one specific stereoisomer: **(2R,3S)-dibrombutane** (or its enantiomer depending on approach) - Anti addition to a double bond yields only **one diastereomer** **Step 5: Why only 1 stereoisomer?** Although there are theoretically $2^2 = 4$ possible combinations of stereochemistry at two centers, the geometric constraint of anti addition through the bromonium ion ensures only **one stereospecific product** forms. **Answer: (A) 1** The stereochemistry is controlled by the anti addition mechanism, which is stereospecific and produces only one stereoisomer.