Question

I feel the OCHEM PAIN!!! SN1, SN2, E1 AND E2 !!!!!!!!!!!!!!!!

Hello there, finals are soon and I still have to understand how these reactions work :(. I get confused by the Polar protic solvent, polar aprotic solvent, strong small base and strong bulky base :(. It'd be amazinf if someone could clearly explain me this concept that I have had so much trouble specially identifying knowing what exactly a is a strong base vs weak base??

Thanks for your time!

Answer 1

Polar solvents have large dipole moments (partial charges). They contain bonds between atoms with large difference in electronegativities, such as oxygen and hydrogen.

Non polar solvents have low dipole moment (lack partial charges). They contain bonds between atoms with similar electronegativities, such as carbon and hydrogen.

A strong base is fully ionic that dissociates into metal ions and hydroxide ions in solution completely.

NaOH --> Na+ + OH-

Ammonia is an example of a weak base. Ammonia doesn't contain hydroxide ions, but it reacts with water to produce ammonium ions and hydroxide ions.

NH3(aq) + H2O <--> NH4+ + OH-

This reaction is reversible, i.e. about 99% of the ammonia is still present as ammonia molecules and only about 1% has actually produced hydroxide ions.

A weak base is one which doesn't convert fully into hydroxide ions in solution.

Bulky bases have high molecular mass. The bulkiness decreases the strength of a base as compared to an equivalent smaller base.

E1 occurs typically with a weak base or no base (acidic conditions and high temperature). E2 occurs with a strong base that can remove weakly acidic hydrogen in a single step.

Since Sn1 and E1 mechanisms proceed via carbocation formation, they are favoured in polar protic solvents.

Sn2 and E2 mechanisms are favored in polar aprotic solvents.