Explain the mechanism of alkaline hydrolysis of tert-butyl bromide with energy profile
Unimolecular nucleophilic substitution(`SN^1`)is a two step reaction process. The first step is a slow step,
while the second one is a fast step. The hydrolysis reaction can be written as follows.
i) Formation of carbonium ion:
a) The C – Cl bond in tertiary butyl chloride slowly dissociates to form chloride ion
(Cl–) and tertiary butyl carbonium ion `[""^+C(CH_3)_3]`
b) This is a slow process and hence, it is a rate determining step (R.D.S).
ii) Formation of the product:
a) The second step is the attack of OH- leading to the C – OH bond formation.
b) It is a fast process
iii) Energy profile diagram:
`Dealta E_1`=Activation Energy For T.S.I
`Dealta E_2`=Activation Energy For T.S.II
`Dealta H`=Heat of reaction
a) The energy profile diagram of the SN1 mechanism explains the independence of the rate reaction on the concentration of nucleophile.
b) The first step in the SN1 mechanism is the formation of carbocation. This step determines the rate of the overall reaction and requires larger activation energy `DeltaE_1`than that of the second step `DeltaE_2`
c) The second step in the SN1 mechanism is the attack of the nucleophile on the carbocation. This step is exothermic and corresponds to a lower energy transition state.
d) The intermediate carbocation appears at a low point in the diagram.
e) The energy difference between the products and the reactants corresponds to the
heat of reaction ΔH.
f) The SN1 reaction is accelerated by the conditions and reagents which favour the
formation of carbocation.
Video Tutorials For All Subjects
- Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Nucleophilic Addition Reactions