E2 with bulky base (Hofmann product): practice and mechanism
The bulky base tert-butoxide only reaches the accessible hydrogens at the edge: the less substituted alkene forms (Hofmann).
Example
Potassium tert-butoxide is very bulky and only reaches the accessible hydrogens at the end of the chain. The less substituted alkene (Hofmann product) is therefore favoured.
Mechanism step by step
- 1
tert-Butoxide is a strong but very bulky base.
- 2
It attacks the sterically most accessible β-hydrogen, usually on a CH₃ group at the edge.
- 3
E2 in the same step: the less substituted alkene forms (Hofmann product).
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which reagent achieves this transformation?
Typical mistakes
- A tert-butyl ether hardly forms: tert-butoxide is too bulky to attack as a nucleophile and only acts as a base.
- An alcohol would come from substitution with water. The bulky, strong base causes elimination here.
Often confused with: E2 (Zaitsev product)
Frequently asked questions
When else does the Hofmann product form?
In the Hofmann elimination of quaternary ammonium salts and generally with poor, bulky leaving groups.
Why does tert-butoxide hardly substitute?
It is too large for a backside attack at carbon, but easily reaches a hydrogen at the edge.