Would this reaction be exothermic or endothermic?

In summary, the conversation discusses the exothermic or endothermic nature of a reaction in which a tertiary allylic alcohol rearranges to become a primary allylic alcohol. The participants consider the entropy of activation and solvent isotope effect as factors in determining the stability of the reactant and product. The discussion also touches on the role of R group induction in stabilizing the carbocation formed in the reaction. Overall, the participants are unsure whether the reaction is exothermic or endothermic due to conflicting evidence regarding the stability of the product.
  • #1
Beowulf_8991
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Summary:: A tertiary allylic alcohol rearranges to become a primary allylic alcohol, would it be exothermic because the final product is more stable and lower in energy?

Hi all, this problem's been on my mind for a couple of days now and I'm not making any progress with it. My problem is that with part c), I can't figure out if the reaction as a whole is exothermic or endothermic; the only data they've given me is that the entropy of activation is +20 Jmol-1K-1 and that the solvent isotope effect value is KH/KD = 0.33.

I think I've figured out the main bulk of the energy diagram but it's the product's energy level that's giving me problems. As far as I understand it, the final product is a tertiary allyl (primary alcohol) but the reactant is a primary allyl (tertiary alcohol) and since the tertiary allyl is a more stable alkene, it should be at a lower energy level therefore making the reaction exothermic. However, the fact it also goes from a tertiary alcohol to a primary one (less stable) makes me think it could be endothermic because of the decreased stability.

It's been a while since I covered energy diagrams so apologies for any rookie mistakes! I'm grateful for any pointers you guys can give me :)
 

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  • #2
To determine the relative stability of the reactant vs the product, try thinking about how the R group induction will stabilize the carbocation formed in the Sn1 reaction.
 
  • #3
Why is a primary alcohol less stable than a tertiary alcohol?
 

1. What is the difference between an exothermic and endothermic reaction?

An exothermic reaction releases energy in the form of heat, while an endothermic reaction absorbs energy from its surroundings.

2. How can I determine if a reaction is exothermic or endothermic?

You can determine the type of reaction by measuring the change in temperature. If the temperature increases, it is an exothermic reaction, and if the temperature decreases, it is an endothermic reaction.

3. What factors can affect whether a reaction is exothermic or endothermic?

The nature of the reactants, the concentration of the reactants, and the presence of a catalyst can all affect whether a reaction is exothermic or endothermic.

4. Can a reaction be both exothermic and endothermic?

No, a reaction can only be either exothermic or endothermic. However, some reactions can have both exothermic and endothermic steps, resulting in an overall change in energy.

5. How do exothermic and endothermic reactions impact the environment?

Exothermic reactions can release energy into the environment, potentially causing an increase in temperature. Endothermic reactions, on the other hand, can absorb energy from the environment, potentially causing a decrease in temperature. Both types of reactions can have significant impacts on the environment and should be carefully controlled and monitored.

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