Consider the following SN2 reaction: a. Draw a mechanism...

Consider the following S$_N$2 reaction: a. Draw a mechanism using curved arrows. b. Draw an energy diagram. Label the axes, the reactants, products, $E_a$, and $\Delta H^\circ$. Assume that the reaction is exothermic. c. Draw the structure of the transition state. d. What is the rate equation? e. What happens to the reaction rate in each of the following instances? [1] The leaving group is changed from $Br^-$ to $I^-$; [2] The solvent is changed from acetone to $CH_3CH_2OH$; [3] The alkyl halide is changed from $CH_3(CH_2)_4$$Br$ to $CH_3CH_2CH_2CH(Br)CH_3$; [4] The concentration of $^-CN$ is increased by a factor of five; and [5] The concentrations of both the alkyl halide and $^-CN$ are increased by a factor of five.

Consider the following S$_N$2 reaction:
a. Draw a mechanism using curved arrows.
b. Draw an energy diagram. Label the axes, the reactants, products, $E_a$, and $\Delta H^\circ$. Assume that the reaction is exothermic.
c. Draw the structure of the transition state.
d. What is the rate equation?
e. What happens to the reaction rate in each of the following instances? [1] The leaving group is changed from $Br^-$ to $I^-$; [2] The solvent is changed from acetone to $CH_3CH_2OH$; [3] The alkyl halide is changed from $CH_3(CH_2)_4$$Br$ to $CH_3CH_2CH_2CH(Br)CH_3$; [4] The concentration of $^-CN$ is increased by a factor of five; and [5] The concentrations of both the alkyl halide and $^-CN$ are increased by a factor of five.

Transcript

00:04 In this problem, we are given the sn1 reaction that's shown here, and we're asked to do a bunch of things.

00:14 First, to show a curved arrow mechanism.

00:17 Next, to draw an energy diagram with labeled axes, including the reactants, the products, the energy of activation, and the delta h.

00:26 And we're told that the starting material and the products are about equal in energy.

00:30 We're asked to draw the transition state if there is one and then the rate equation and then how the rate changes in the following conditions.

00:47 So first things first, we can start with our curved arrow mechanism.

00:55 I'm going to redraw it just below and a little bit smaller.

01:00 So here is our starting material.

01:06 And we remember the first step in any sn1 reaction is to have the leaving group leave.

01:20 So our iodine is going to leave.

01:25 And now we'll have our carbocadion intermediate and our iodine that's left.

01:39 Then our solvent water or our weak nucleophile is going to come in and it will attack.

01:54 And it can go front or back, but it'll form a racemic mixture if this were a stereocenter, but it's not because those muffler groups are equivalent.

02:17 And that is the arrow -pushing mechanism for this.

02:21 Next, we're going to draw our energy diagram.

02:29 I'm going to draw my kind of rough graph here.

02:35 And on the y -axis, we're going to have our energy, and the x -axis will be our reaction progress.

02:51 That axis can go by a number of names, including time, just reaction.

02:56 I like reaction progress.

03:00 Now, since we're told that the story starting material and the products are about equal in energy, i'm going to draw them sort of arbitrarily about here.

03:13 Then i'm going to draw my starting material, which is just our alkalahalide.

03:27 And our final product is going to be the water substituted alkaline.

03:43 Now, because this this is an sn2 reaction.

03:48 We're going to have two bumps of energy.

03:55 That's because we have to overcome the energy to make our leaving group leave.

04:02 And then again for our attacking group to attack.

04:09 So i'm going to draw this going up and down.

04:18 And then up again and then down.

04:30 So because we have two peaks, we're gonna have two transition states and an intermediate in this energy well here.

04:40 The first transition state is where our leaving group is in the middle of leaving.

04:48 So i'm gonna draw this in a different color just to try to make it even clearer.

04:56 And i'm going to be a little bit more explicit with my groups here.