Question

Does the Carboxylic acid of tyrosine get deprotonated by NaH? If so, why is it not alkylated by the alkyl halide? Comment on nucleophilic strength, and again use structures to explain your answer Alkyl halide is EtBr

Answer 1

Yes, the carboxylic acid of tyrosine gets easily deprotonated by NaH.

To answer the second part of the question, it is important to mention that there are two types of sustitution in organic chemistry. According to the solvent, nucleophile and substrate it can be: SN1 and SN2. (there is also NSi reaction)

SN1 reaction needs the formation of a positive carbon (determining step for reaction). So, any type of linear alkyl halide as ethyl bromide can not support that step, due to lack of negative charge from the alkyl gruop to donate to the positive carbon.

SN2 reaction depends on among many things, how easily/strengh nucleophile attacks as well as it doesnt need the formation of a positive carbon.

Therefore, if there any reaction, it comes from SN2.

Tyrosine has three nucleophiles: the carboxylate anion, the amine group and the hydroxyl gorup.

The carboxylate anion is not a good nucleophile for SN2 reaction because of the continuous movement of their electrons. This condition doesnt allow an efficient attack as the amino and hydoxy groups have. Between those two, the amino gruop will be the candidate for SN2 reaction with EtBr, because it has higher electronegativity.

hope this answer help you