C-protected ester question for any brilliant minds out there

[Trela]

Hey guys,

 

Does anyone know if question 6B is to do with the resulting carbocation being stabilised by an electron-donating methyl group in the R1 position, etc?

 

And more stabilisation if R2 is Ph?

 

So R1=ME, R2=Ph is most stable and the one with both R1 and R2 as H is least stable??

 

 

http://www.chem.canterbury.ac.nz/courses/tests_exams/2004texams/exams/chem262.pdf

 

P.S. If poss, any thoughts on question 4a here would be appreciated too:

http://www.chem.canterbury.ac.nz/courses/tests_exams/2006texams/endofyear/chem262.pdf

[Tartaglia]

The methyl groups in the R1 positions stabilise the carbocation by the inductive effect. The aromatic ring stabilises the carbocation by the conjugative effect. The more extensive pi system with the extra phenyl group in R2 position leads to more stabilisation as the positive charge can be delocalised throughout the coplaner two ring pi system