New organic mechanisms
Two new mechanisms
- A Level adds two reaction mechanisms.
- Electrophilic substitution is how benzene reacts.
- Addition–elimination appears with some reagents.
Practice
Electrophilic substitution is when:
Benzene reacts by electrophilic substitution, keeping its stable ring while swapping an H for the electrophile.
Practice
Benzene reacts mainly by:
Substitution keeps the stable delocalised ring intact, unlike addition which would destroy it.
Electrophilic substitution
- An electrophile replaces a hydrogen atom on a benzene ring.
- This is the characteristic way benzene reacts (the stable ring is kept).
Practice
In an addition–elimination reaction:
Addition–elimination (e.g. with 2,4-DNPH or acyl chlorides) adds then eliminates a small molecule.
Addition–elimination
- A molecule first adds on, then a small molecule is removed.
- Seen with 2,4-DNPH (with carbonyls) and with acyl chlorides.
You've got it
Key idea
- electrophilic substitution: an electrophile replaces an H on the benzene ring (how benzene reacts)
- addition–elimination: a molecule adds on, then a small molecule is removed (e.g. 2,4-DNPH, acyl chlorides)