Would the following molecules react by Sn1 or Sn2 mechanism: 1-methyl-1-bromo-cyclohexane and 2-bromohexane?

First, let me preface by saying that no reaction is necessarily #100%# #S_N1# or #S_N2#. In many cases, at a suitable temperature, it is a mix of the two. Here is a set of reactions from a 2013 O-Chem worksheet that I did:

Some things I could define:

• The compound under each arrow is a solvent.
• #"Bu"# is shorthand for #"CH"_3"CH"_2"CH"_2"CH"_2-#, or butyl.
• When I wrote substitution, I included both #S_N1# and #S_N2# under one umbrella, and similarly, when I wrote elimination, I mean both #E1# and #E2# combined.

  That aside, let's see.

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  MAIN POINTS ABOUT SN1 AND SN2

  See the following for an overview on these types of reactions:
  https://tutor.hix.ai

  1-BROMO-1-METHYLCYCLOHEXANE

  1-bromo-1-methylcyclohexane is a tertiary cyclohaloalkane. It means it has steric hindrance on carbon-1. Therefore, it is more likely to commit to #S_N1# than #S_N2#.

  Why? Because the steric hindrance makes it more difficult to come up from behind and backside-attack. There's too much bulk and obstruction around the target site that it isn't easy for the reactant to get to where it needs to.

  2-BROMOHEXANE

  This is where it gets tricky. It is a secondary haloalkane, so it's anyone's guess as to whether #S_N1# or #S_N2# predominates, depending on the solvent conditions...

  If I had to guess, I would say in general, #S_N1# is more prominent by a small margin because secondary haloalkanes have some steric obstruction, but not as much as a comparable tertiary haloalkane.

  As to what extent #S_N1# predominates, I wouldn't know. All we can say without definitive data to prove it is that #S_N1# is more prominent than #S_N2#.