Question

Derive and explain Acid Catalyzed Ring Opening

Answer 1

It's easy to understand the mechanism in case of epoxides:
 The acid-catalyzed ring-opening reaction of epoxides follows a mechanism with S_N2 features (inversion of stereochemistry, no carbocation rearrangements), the mechanism is not strictly a S_N2 mechanism.

Further
 The transitition state has more progress toward the C-LG bond breaking than an S_N2, but more progress toward the C-Nu bond forming than S_N1. There is significantly more δ+δ+ character on the carbon than in S_N2, but not as much as in S_N1.
 The transition states are:




 

Now examples are:




The overall order of selective nature is 3^o > 2^o > 1^o.