1) tert-Butyl chloride reacts by substitution at virtually the same rate in pure
water (where the hydroxide ion is 10–7 M) as it does in 0.05 M aqueous sodium
hydroxide (where the hydroxide ion concentration is 500,000 times larger).
2) The rate equation for this substitution reaction is first order respect to
tert-butyl chloride and first order overall.
(CH 3 ) 3 C + OH− H
2 O +
Cl acetone (CH 3 ) 3 C OH Cl−
Rate ∝ [(CH 3 ) 3 CCl] ⇒ Rate = k [(CH 3 ) 3 CCl]
- Hydroxide ions do not participate in the transition state of the step that controls
the rate of the reaction.
- The reaction is unimolecular ⇒ SN 1 reaction (Substitution, Nucleophilic,
Unimolecular).
6.10A MULTISTEP REACTIONS AND THE RATE-DETERMINING STEP
- The rate-determining step or the rate-limiting step of a multistep reaction:
Step 1 Reactant slow Intermediate 1 ⇒ Rate = k 1 [reactant]
Step 2 Intermediate 1 fast Intermediate 2 ⇒ Rate = k 2 [intermediate 1]
Step 3 Intermediate 2 fast Product ⇒ Rate = k 3 [intermediate 2]
k 1 << k 2 or k 3
1) The concentration of the intermediates are always very small because of the
slowness of step 1, and steps 2 and 3 actuallu occur at the same rate as step 1.
2) Step 1 is the rate-determining step.
