Synthesis via Sn2/Sn1, E2, E1

[alingy1]

Hi all,
I was looking at the answers in my textbook. They seem to make incongruent choices of solvents.

In e) and j), why choose EtOH and H2O/CH3OH? I would rather choose an aprotic solvent like DMF to better allow Sn2 to occur. Especially with j), there is a lot of competition with E2 because OH- is a strong base and because we are attacking a secondary carbon.

 

[alingy1]

I see this again in k). Secondary carbon attacked: why not add DMF to prevent E2 and get best yield?

 

[Teemo]

Depends on the acidity/basicity of the end product. A reaction proceeds towards the weaker base/acid. If your end products are more acidic or basic than the reactants, it will not occur.

 

[alingy1]

Teemo, I don't see how an unreacting reagent can cause a change in acid base interactions.

 

[DeeNos]

I would like to first address the concept of synthesis via Sn2/Sn1, E2, and E1 reactions. These are all different types of substitution and elimination reactions, which are commonly used in organic synthesis to create new compounds. The choice of which reaction to use depends on the starting materials and desired product.

In regards to the choice of solvents, it is important to consider the nature of the reaction and the stability of the reactants and products. For Sn2 reactions, a polar aprotic solvent like DMF is often preferred because it can solvate the nucleophile and decrease the solvation of the leaving group, allowing for a faster reaction. On the other hand, for Sn1 reactions, a polar protic solvent like EtOH can stabilize the carbocation intermediate and promote the reaction.

In the case of E2 and E1 reactions, the choice of solvent is also important. Aprotic solvents favor E2 reactions, while protic solvents favor E1 reactions. In the given examples, the use of EtOH and H2O/CH3OH as solvents may be due to the reagents and reactants being used, as well as the desired product.

It is also important to note that the choice of solvent can also affect the selectivity of the reaction. In the case of j), the use of a polar protic solvent may be preferred to promote the E1 reaction, as the secondary carbon being attacked may not be as reactive in an Sn2 reaction.

Overall, the choice of solvent in organic synthesis is a complex decision that requires consideration of various factors. As scientists, it is important to carefully consider the nature of the reaction and the stability of the reactants and products when choosing a solvent for a specific synthesis.