What effect would you expect the following changes to have...

What effect would you expect the following changes to have on the rate of the reaction of ethanol with 2 -iodo-2-methylbutane?
(a) The concentration of the halide is tripled.
(b) The concentration of the ethanol is halved by adding diethyl ether as an inert solvent.

Key Concepts

SN1 Reaction Mechanism

An SN1 mechanism involves a two-step process where the first, slow step is the formation of a carbocation intermediate from the substrate. This step is unimolecular, meaning that the overall reaction rate depends solely on the concentration of the substrate undergoing ionization.

Rate Law Specificity

In an SN1 reaction, the rate law is determined by the unimolecular ionization step and is expressed as rate = k[substrate]. This means that only the concentration of the substrate directly influences the overall rate, while the nucleophile’s concentration does not affect it significantly.

Effect of Reactant Concentration Changes

Because the rate-determining step in an SN1 reaction depends solely on the substrate's concentration, increasing the concentration of the substrate proportionately increases the reaction rate. Conversely, altering the concentration of the nucleophile does not affect the rate-determining step, so changes in nucleophile concentration have little to no effect on the overall reaction rate.

Solvent and Dilution Effects

Using an inert solvent to dilute the reaction mixture can change the concentrations of the reactants. However, for a reaction proceeding via an SN1 mechanism, dilution of the nucleophile does not impact the rate-determining formation of the carbocation, and thus has minimal effect on the reaction rate.

Transcript

00:01 So we have the following organic compound.

00:03 We have two iota, two methylbutane, and we want to know, we're going to react it with ethanol, and we want to know what would happen to the rate of this reaction, given the following reaction conditions.

00:13 Well, first, we have to know what kind of reaction it is in order to determine how the rate will be affected.

00:18 And we see that we have a iota, tertiary iota group, and therefore it's likely, since our ethanol is a weak movement file, that this is going to occur via an sn1 type reaction.

00:34 However, ethanol may also act as a weak base, depending on how much heat is added into the reaction, we may get an e1 elimination reaction as well.

00:44 So we can predict the products to look something like this, where we will go ahead and replace our iota group with the hydroxide group for our sn1, and for our elimination, it's going to look something like this.

01:10 Where we get the major product is this because of zyte -sebs rule.

01:19 So what's important to realize here is that we have, whether it's an s -n -1 or e -1 reaction, is that they're both the unimolecular.

01:30 So that the rate of this reaction only depends on our alkali, because we have to remember that these reactions proceed via a carbocadion intermediate, and the rate limiting step is our leaving group, which is how fast our leaving group leaves.

01:47 And therefore our rate is going to depend on the concentration of our iota group or our alkylo halide.

02:00 So we would say that at the rate depends only on the concentration of alkyl halide, which we go ahead and write rx here...

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