Question

Why neopentyl bromide show sn2 reaction with etoxide and sn1 reaction with ethanol??

Answer 1

The SN2 reaction is not impossible, but really slow, due to steric hindrance. (For instance, ethyl bromide is ~40,000 times more reactive through SN2 than neopentyl bromide.)

So, as a matter of fact, we actually have four possibilities.

1. Neither SN2 nor E1/SN1 is are enough to take place to any notable extent.

2. Both reactions take place to a notable extent.

3. Only SN2 takes place to a notable extent. 

4. Only E1/SN1 takes place to a notable extent.