1. Carbocation Stability:
* Tertiary Butanol: Dehydration of tertiary butanol forms a tertiary carbocation intermediate. Tertiary carbocations are the most stable type of carbocation due to the electron-donating effect of the three alkyl groups, which stabilize the positive charge.
* n-Butanol: Dehydration of n-butanol forms a primary carbocation intermediate. Primary carbocations are the least stable due to the lack of electron-donating groups to stabilize the positive charge.
2. Steric Hindrance:
* Tertiary Butanol: The bulky tert-butyl group makes it difficult for water molecules to approach the carbon bearing the hydroxyl group. This steric hindrance makes the protonation step of the dehydration reaction slower. However, once the carbocation is formed, it is more stable and the subsequent elimination of water is much faster.
* n-Butanol: The smaller n-butyl group has less steric hindrance, allowing water molecules to approach the hydroxyl group more easily. This makes the protonation step faster, but the resulting primary carbocation is unstable and the elimination step is much slower.
3. Reactivity of the Alcohol:
* Tertiary Butanol: Tertiary alcohols are more reactive towards dehydration because the carbon-oxygen bond is weaker due to the electron-donating effect of the alkyl groups.
* n-Butanol: Primary alcohols are less reactive towards dehydration because the carbon-oxygen bond is stronger.
In summary:
The faster rate of dehydration of tertiary butanol compared to n-butanol is primarily due to the greater stability of the tertiary carbocation intermediate. This stability outweighs the slightly slower protonation step caused by steric hindrance.
Simplified Explanation:
Think of it like this: Tertiary butanol forms a more "happy" and stable carbocation intermediate, which makes the whole dehydration process go faster. n-Butanol forms an unstable and "unhappy" carbocation, making the process slower.
