Flashcards · 7405 · A Level Topic 25

Optical isomerism (A Level) flashcards

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Chiral centre (asymmetric carbon): A carbon atom bonded to four different atoms or groups.
Enantiomers: Non-superimposable mirror images that differ in their effect on plane-polarised light.
Racemic mixture (racemate): A mixture of equal amounts of the two enantiomers. It is optically inactive.
Why is a racemate optically inactive?: Each enantiomer rotates the plane of plane-polarised light by the same angle in opposite directions, and there are equal amounts of each, so the effects cancel.
Why does a reaction at a planar group give a racemate?: The planar group (C=O or a carbocation) can be attacked from either side with equal probability, giving equal amounts of the two enantiomers.
Which carbon in butan-2-ol is chiral, and what are its groups?: C2: it carries H, OH, CH₃ and C₂H₅.
Optically active vs racemate: A single enantiomer is optically active; an equal mixture is not, even though every molecule in it is chiral.