Draw the transition state for each reaction.

Name: Problem 40, Chapter 6: Organic Chemistry
Uploaded: 2019-05-09T03:22:16-08:00
Duration: 6 min 2 s
Channel: Nima Gharibi
Description: Draw the transition state for each reaction.

Key Concepts

Transition State

In chemical reactions, the transition state is a fleeting, high-energy arrangement of atoms at the peak of the energy barrier that separates reactants from products. It represents the point where bonds are partially broken and formed, and its structure is critical in determining the rate and outcome of the reaction.

Transition State Theory

Transition state theory provides a framework for understanding reaction rates by postulating that reactants must first form a high-energy transition state before converting into products. This theory allows chemists to estimate the activation energy and predict how changes in temperature and structure affect the reaction rate.

Reaction Coordinate Diagram

A reaction coordinate diagram is a graphical representation of the energy changes that occur during a chemical reaction. It plots the potential energy along the reaction pathway, highlighting the energy of the transition state as the highest point—often referred to as the activation energy barrier.

Hammond Postulate

The Hammond Postulate relates the structure of the transition state to the structures of the nearest stable species (either reactants or products). It suggests that for endothermic steps the transition state more closely resembles the products, while for exothermic steps it resembles the reactants, providing insight into the transition state's structure.

Bond Formation and Bond Breaking

At the transition state, bonds within the reacting molecules are in the process of breaking and forming simultaneously. This dual process means that no bond is completely intact or broken; rather, bonds exhibit partial characteristics, which is key to understanding and depicting the transition state in a reaction mechanism.

Transcript

0:00 Hello everyone.

00:01 Today we're doing problem 6 .40 and this problem asks us to draw the transition state for each of the following reaction.

00:07 So we see that we have cyclohexane attached to some sort of halide.

00:13 This case is bromine and we're breaking it up to a carbocadion intermediate with a bromide anion.

00:19 So remember the transition state is the point of a reaction where bonds are being made and broken.

00:25 So your reactant bonds are breaking and your product bonds are forming.

00:30 So in the transition state is the point of reaction where bonds are being made and broken.

00:30 In this case, we know that the sigma bond between this carbon bromine must break.

00:36 So i can draw the transition state and transition states are drawn in squared brackets.

00:43 So our transition state is the reactant bonds breaking and the product bonds forming.

00:48 Well, here there's no real products.

00:50 We only have the reactant bonds breaking, which is the sigma bond, which is these dotted lines, and is attached to the bromine.

00:58 And in this case, bromine is going to be getting an extra lone pair of electrons because of the heterolithic cleavage.

01:05 So we know that there's going to be a delta minus sign here, while we're forming a carbocations with electron pore site at the carbons that's going to be delta positive here.

01:15 So this is a transition state for this reaction.

01:19 In this product, in this reaction scheme, we're given that we are going to use this chloride anion and nucleophilically attack this bromine center.

01:29 And we're going to form our product here.

01:33 So if i draw my transition state, remember, transition state is shown in squared brackets, and my starting material bonds are going to be breaking as my product bonds are forming.

01:49 So there's nothing actually breaking here, but there's always going to be a formation of a new bond, which is going to be shown in dotted lines, attached to my chlorine nucleus, and you can actually put a double dagger here to indicate it's a transition state.

02:07 So it's actually this double dagger, double positive sign actually means that it's a transition state.

02:13 And if you recall, my bromine is going to get extra electrons because it's negatively charged.

02:18 And my chlorine was also negative.

02:20 So both of these are delta negative.

02:26 If you go to the third example, we see that we're actually doing some sort of proton abstraction.

02:33 So from neutral alcohol, we're going to negatively charged oxygen anion, and we're actually neutralizing this nitrogen product to make ammonia.

02:48 So we are actually forming and breaking bonds here.

02:50 So this is a good example.

02:52 Remember your transition state on a squared brackets and you can draw your double -headed arrows to indicate the transition state...

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