How are SN1 reactions written?

1 Answer
Feb 25, 2018

#"S"_"N"1# reactions are stepwise, unimolecular substitution reactions. They usually undergo 2-5 steps: here's a mechanism I made up (more representative of solvolysis, a process that takes on this substitution mechanism),

Since the rate-determining step is the loss of a leaving group, we want excellent leaving groups. Moreover, since #"S"_"N"2# mechanisms want strong nucleophiles for the same reason, an average strength nucleophile works in unimolecular substitution (hence why we can use a neutral nucleophile like methanol).

Afterward, the intermediate with the positively charged oxygen is too high in energy to be very stable, so methanol will deprotonate it to the give the molecule I made at the end.

These take a lot of practice, and this is normally where organic chemistry gets hard for students (and where I see lots of drops and quiz/exam fails, unfortunately). Get it together or surrender is what I say. :)