Stereochemistry & Isomerism
Spin the back carbon and watch a meso compound lock onto its own mirror image at the anti conformation — and watch the (±) form refuse to. Builds the cis/trans × syn/anti → meso/(±) intuition behind NEET 2025 Q51.
Slider = dihedral (back-carbon rotation). Toggle the alkene & reagent to set up the product, then snap to anti.
5 minutes · +4 right, −1 wrong (real NEET marking) · one global leaderboard.
Change either the alkene geometry (cis/trans) or the addition mode (syn/anti) and the answer flips between meso and (±); change both and it stays the same. Concretely: anti addition gives meso from trans and (±) from cis, while syn addition gives meso from cis and (±) from trans.
meso-ness is a property of configuration, but the centre of symmetry only becomes visually obvious in the anti (180°) Newman projection. In a skew or gauche conformation the symmetry is hidden, so you must rotate the back carbon to anti before checking. NEET 2025 Q51 deliberately drew the glycol skewed to exploit this.
No. A meso compound has stereocentres but also an internal plane or centre of symmetry, so its mirror image is superimposable on itself. The rotations from its two halves cancel internally, making it optically inactive (achiral) despite having chiral centres.
Cold dilute alkaline KMnO₄ does syn dihydroxylation: it forms a cyclic manganate ester across one face of the C=C, so both –OH groups end up on the same face. With cis-but-2-ene this syn addition yields the meso diol; with trans-but-2-ene it yields the (±) pair.
Statement I: trans-but-2-ene + Br₂/CCl₄ ka product (±)-2,3-dibromobutane ke roop me draw kiya gaya hai. Statement II: cis-but-2-ene + alkaline KMnO₄ ka product meso butane-2,3-diol ke roop me draw kiya gaya hai. Sahi option chuno: