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I did an experimtent about the reactivity of alkyl halides last week.
In the experiment, I needed to add NaI in acetone into 2-chlorobutane and 2-chloro-2-methylpropane solution but I found that 2-chlorobutane were no observation and 2-chloro-2-methylpropane gave deep yellow solution .

I guess that 2-chlorobutane is a secondary alkyl halide and it could undergo either Sn1 or Sn2 mechanism while 2-chloro-2-methylpropane is a tertiary alkyl halide to undergo Sn1.

I found some information from the Internet, the secondary alkyl halide will undergo Sn1 in the presence of weak nucleophiles. In a polar aprotic solvent, iodide ions become weak nucleophile. So, 2-chlorobutane proceed on Sn1 mechanism in this experiment.

In Sn1, the reactivity of tertiary > secondary > primary, so I can conclude that the reactivity of 2-chloro-2-methylpropane > 2-chlorobutane. Am I right?
Thank You!