Why does a tertiary halide give a racemic (mixed left/right) product while a primary one gives a single mirror image?
A tertiary halide reacts by SN1 through a flat, planar carbocation.
A tertiary halide reacts by SN1 through a flat, planar carbocation. The nucleophile can then attack from either face with equal ease, so you get both mirror-image products — a racemic mixture. A primary halide reacts by SN2: the nucleophile attacks from directly behind the leaving group, flipping the centre like an umbrella (inversion), so you get one specific configuration.
Key point
SN1 (planar carbocation) racemises; SN2 (backside attack) inverts the configuration.
Common mistake
expecting both mechanisms to preserve the original geometry.
Memory tip
flat carbocation → attack from both sides → racemic; SN2 → clean inversion.
Tap to watch or see it right here — the app stays open (it only opens a quick search if nothing embeddable is found).