Draw the products obtained from the reaction of one...

Key Concepts

Resonance Stabilization

Resonance stabilization in organic reactions involves the delocalization of electrons across multiple atoms. For reactions involving conjugated systems, resonance can stabilize cationic intermediates by spreading the positive charge over several atomic centers, impacting the regioselectivity and overall product distribution in the reaction.

Conjugated Polyene Reactivity

Conjugated polyenes, with alternating double and single bonds, exhibit delocalized ? electrons that can stabilize intermediates through resonance. Their reactivity in electrophilic additions is affected by this delocalization, allowing for the formation of multiple regioisomers and influencing whether the reaction follows kinetic or thermodynamic pathways.

Electrophilic Addition Mechanism

The electrophilic addition mechanism involves the attack of an electron?deficient species (electrophile) on a conjugated system, such as a polyene. In this mechanism, protonation of the double bond creates a carbocation intermediate, which can then be attacked by a nucleophile (such as bromide ion), leading to addition products.

Thermodynamic Control

Thermodynamic control describes a situation where the product distribution reflects the relative stability of the products, achieved under conditions (typically higher temperatures or longer reaction times) that allow the intermediates to equilibrate. In such cases, the most stable product, even if it forms more slowly, eventually predominates.

Kinetic Control

Kinetic control refers to conditions in which the product distribution is determined by the relative rates at which products form rather than by their ultimate stability. Under these conditions, the product that forms the fastest (often via the least?energetic transition state) predominates, even if it is less thermodynamically stable.

Transcript

00:04 This question asks us to draw the products from the reaction of 1 -35 hexatriene, which is this structure with hbr, and then asks us what products will predominate under kinetic control and under thermodynamic control.

00:18 So this is a triene.

00:21 So we're going to do this just like a dying reaction, but instead of just having the 1 -2 and the 1 -4 products here, now we'll have a 1 -6 as well.

00:29 So here, since this is the same on both sides, it doesn't matter which side we start from.

00:34 So i'm just going to start from this side over here.

00:36 We'll call this one and this six.

00:38 So two, three, four, five.

00:40 And our carbocadions are going to be on two, four, and six.

00:44 Normally they're on two and fours.

00:45 So we're just adding the six on because it's the trying.

00:48 So the first step is for the one, two, double bond to grab the hydrogen and we'll kick the bromine off.

00:53 That'll leave us with this bromine nucleophile left over.

00:57 And then the first carbocation that we'll get will look like this.

01:01 It'll be on carbon two.

01:02 The h from the bromine went on to the first carbon over here to allow the carbocadine to be on the more stable carbon right here on carbon 2.

01:11 And then we'll get some resonance here.

01:14 So if we move this like this, we get another resonance contributor of this structure that looks like this.

01:21 So now our carbocadion is over here.

01:24 And then if we move this one more time, we get another structure that looks like this with the carbocatine here on the end.

01:32 So then we can have the bromine nucleophile attack each one of these carbokadines to give us three different products.

01:41 So this first one will be our one -two product and we'll have the bromine here on carbon two.

01:46 So this is one -two...

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