3.07. Optical Isomerism

What is optical isomerism?

A form of stereoisomerism where molecules have the same molecular formula and structural formula but different arrangements of atoms in space (due to chirality). :contentReference[oaicite:1]{index=1}

What must a carbon atom have for a molecule to show optical isomerism?

Four different substituents attached to it (chiral centre). :contentReference[oaicite:2]{index=2}

What is a chiral centre?

A carbon atom that has four different groups attached, creating a non‑superimposable mirror image. :contentReference[oaicite:3]{index=3}

What are the pair of isomers called that result from optical isomerism?

Enantiomers — non‑superimposable mirror image molecules. :contentReference[oaicite:4]{index=4}

How are optical isomers similar?

They have the same atoms and bonds and identical physical properties like melting point or boiling point. :contentReference[oaicite:5]{index=5}

How do optical isomers differ?

They rotate plane‑polarised light in opposite directions by equal amounts. :contentReference[oaicite:6]{index=6}

What word describes molecules that show optical activity?

Chiral. :contentReference[oaicite:7]{index=7}

What is an racemic mixture?

A 50:50 mixture of two enantiomers that shows no net rotation of plane‑polarised light. :contentReference[oaicite:8]{index=8}

Why does a racemic mixture show no optical activity?

Because the rotations caused by each enantiomer cancel each other out. :contentReference[oaicite:9]{index=9}

Why do reactions that produce a chiral centre often produce a racemic mixture?

Because a planar intermediate can be attacked equally from either side, forming both enantiomers. :contentReference[oaicite:10]{index=10}

How can separate samples of enantiomers be distinguished experimentally?

By observing the direction they rotate plane‑polarised light using a polarimeter. :contentReference[oaicite:11]{index=11}

What is optical activity?

The ability of a chiral compound to rotate the plane of polarised light. :contentReference[oaicite:12]{index=12}

What does it mean if a molecule is achiral?

It is superimposable on its mirror image and will not show optical isomerism. :contentReference[oaicite:13]{index=13}

What kind of isomerism includes optical isomerism?

Stereoisomerism. :contentReference[oaicite:14]{index=14}