Hey guys,

 

Once again, I am going through practice exams in preparation for my MCAT.

 

For the third one, I am not too sure if -OMe is the nucleophile or if it was a -Cl ion. However, due to the common ion effect and MeOH being the solvent, I am pretty sure it is the former.

 

As for the fourth question, just out of curiosity, electronics effects for epoxides only dominate in acidic conditions and only when comparing third to first degree carbons. Therefore, it is not even a concern in this question since we are using basic conditions, correct?

 

Thanks.

 

 

For the third one, the HCl acts to protonate the alcohol to generate a water leaving group. The oxygen on the methanol is the nucleophile. Note that this is not the same as -OMe. You don't generate the alkoxide in this (it's an acidic solution, so you shouldn't have negative charges floating about).

 

For number 4, I'd say it's more to do with steric repulsion.