Which of the following reactions will go faster if the concentration of the nucleophile is incre

Which of the following reactions will go faster if the...

Key Concepts

SN1 Reaction Mechanism

The SN1 mechanism is a unimolecular nucleophilic substitution reaction where the rate-determining step is the formation of a carbocation intermediate from the substrate. This step does not involve the nucleophile, which means the overall reaction rate depends solely on the concentration and stability of the substrate. Consequently, changes in the nucleophile concentration have little or no effect on the speed of an SN1 reaction.

Reaction Kinetics and Rate Laws

Reaction kinetics involves the study of how the concentration of reactants influences the rate of a chemical reaction. In bimolecular reactions (such as SN2), the rate is dependent on the concentrations of both reactants involved in the transition state, whereas in unimolecular reactions (such as SN1), the reaction rate is determined by the formation of an intermediate and is independent of the nucleophile's concentration. Understanding these distinctions is crucial when predicting how varying concentrations will affect overall reaction rates.

SN2 Reaction Mechanism

The SN2 mechanism is a bimolecular nucleophilic substitution reaction where the rate-determining step involves both the substrate and the nucleophile. In these reactions, the nucleophile attacks the substrate at the same time as the leaving group departs, leading to a transition state that simultaneously involves both reactants. Because the rate law for SN2 reactions is of the form rate = k [substrate][nucleophile], increasing the concentration of the nucleophile directly increases the reaction rate.

Transcript

00:01 Okay, so for this problem, you're given three different reactions, and you're told if you double the concentration of the nucleophile, in which of these problems would the reaction go faster? so before we do that, we need to figure out which of these reactions are going to be sn1 or sn2.

00:24 And the reason that we need to do that is we have to think back to our rate equations.

00:29 So for sn1, if you remember, the rate of the reaction is going to be equal to k times the concentration of your hallow alkane.

00:42 For sn2 reactions, the rate is a little bit different.

00:47 So in this case, the rate is going to be equal to k times the concentration of your hallow alkanes times the concentration of your nucleophile.

00:57 So the question, because it's asking, which are the reactions if you increase the concentration of the nucleophile is also going to cause an increase in the rate? you have to think about sn2 reactions because in this rate equation, your nucleophile is comparable to your rate.

01:22 So whichever of these reactions is sn2 is going to be our answer to the question.

01:27 So let's look at this first example.

01:31 So here we have a secondary alkyal halide, called rx, and now, you know, secondary alkali halides can either go sn1 or sn2 reactions, depending on the reaction conditions.

01:53 So in this case, because this is a chirocarbon, kind of a hint that we can do to figure out if this is sn1 or sn2, is look at the configuration of the stereochemistry of our product.

02:07 And if you look at the stereochemistry of our product, we have, there should be a hydrogen on this atom here.

02:14 And actually, i think i drew this.

02:19 Oh, yeah, this is, sorry about that.

02:23 Let's fix this up.

02:28 Okay, so for this problem, we actually have an inversion of stereochemistry, of stereochemistry...

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