Name

Structure

Class

S_N1
AgNO₃ in EtOH

S_N2

NaI in
DMK

probing questions that need to be addressed in your comments /conclusions

2^o Cl

+

+

∙Which is the better leaving group, Cl⁻ or Br⁻?
∙Why?

∙What is the order of reactivity with respect to R for S_N1?

∙S_N2?

∙Explain why these orders are observed.

2^o Br

++

++

1^o Cl

~0

++

1^o Br

~0

+++

3^o Cl

++++

~0

1^o allylic Cl

++++

++++

∙What is the effect of neighboring [b,g] conjugation on S_N1? ∙Why?
you might need to take a quick look at Carey pp 366-368
∙What is the effect of neighboring [b,g] conjugation on S_N2? ∙Why?
see below

1^o benzylic Cl

++++

++++

chloroacetone
(1-chloro-2-propanone)
<was not in your expt>

1^o Cl with
a-carbonyl

~0

++++

S_N1: presence of the d⁺ on the neighboring b-C suppresses the  formation of the carbocation intermediate and negates any possible resonance stabilization effects from the neighboring p-system
S_N2:  the neighboring p-system can stabilize the pentacoordinate sp² C in the transition state, and the presence of the d⁺ on the neighboring b-C actually provides inductive assistance in this stabilization, since the [I---C---Cl]^‡  TS is negatively charged.

aromatic Br

0

0

∙Why are aromatic halides resistant to both S_N1 and S_N2?

cyclic 2^o Br

1.5+

1.5+

∙Why is cyclopentyl bromide less reactive in S_N1 than cyclohexyl bromide?
∙Why are cyclic 2^o bromides significantly less reactive than open-chain 2^o bromides in S_N2?
∙Why is cyclohexyl bromide so much less reactive in S_N2 than cyclopentyl bromide?

 cyclic 2^o Br

++

~0