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Two part question for you. Let's preface this with I'm in organic chemistry 1, so we're just learning the basics of these reactions.

  1. Are neopentyl halides completely inert to any reaction through any pathway, $\mathrm{S_N1, S_N2, E1, E2}$? For $\mathrm{S_N1/E1}$, even after solvolysis of the halide, is there too much steric strain there for anything to attack the carbocation? Even a small base like $\ce{MeO-}$?

  2. Can a methyl iodide/bromide undergo $\mathrm{S_N2}$ with any basically any nucleophile since there's practically no steric hindrance? Even a bulky compound that's not very lewis basic like tButanol?

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Carey-Sundberg has some answers (vol. A, chapter 4). The text is a bit advanced for you at the present stage, but you should give it a try.

It gives as reference JACS 1975, 97, 3694. That paper has rate constants for nucleophilic substitution of compounds of type $\ce{RCH2Br}$, with $\ce{R=H, Me, Et, i-Pr, t-Bu }$ with $\ce{LiCl}$ in acetone at room temperature.

Rate constants in 105 s-1: $\ce{R=H}$: 600, $\ce{R=Me }$: 9.9, $\ce{R=Et}$: 6.5, $\ce{R=i-Pr}$: 1.5, $\ce{R=t-Bu }$: 2.6*10-4

Nucleophilic substitution does take place in neopentyl halides, but at a rate of five orders of magnitudes less than in less hindered compounds.

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