How can I rank these substrates from fastest to slowest reacting? In an SN2 reaction with NaI-Acetone? Based on theory alone?

benzyl chloride
n-butyl bromide
n-butyl chloride
sec-butyl chloride
tert-butyl chloride

To rank these substrates from fastest to slowest reacting in an SN2 reaction with NaI-Acetone, you can consider the principles of nucleophilic substitution reactions and the effects of various factors on reaction rate.

In an SN2 reaction, the nucleophile (in this case, NaI) attacks the substrate's carbon atom while a leaving group (chloride or bromide) is simultaneously displaced. The rate of an SN2 reaction depends on the strength of the nucleophile, the stability of the leaving group, and the steric hindrance around the reaction center.

1. Determine the strength of the nucleophile (NaI): Iodide (I-) is a stronger nucleophile than chloride (Cl-). Therefore, NaI is a stronger nucleophile than NaCl.

2. Consider the stability of the leaving group: Bromide is a better leaving group than chloride due to its larger size and the weaker carbon-bromine bond. Therefore, n-butyl bromide is more likely to undergo an SN2 reaction compared to n-butyl chloride.

3. Analyze the steric hindrance around the reaction center: Steric hindrance occurs when bulky substituents or groups hinder the approach of the nucleophile. The greater the steric hindrance, the slower the reaction.

Using this information, let's rank the substrates:

1. n-butyl bromide: It has a stronger nucleophile (NaI) and a better leaving group (bromide).
2. n-butyl chloride: It has a stronger nucleophile (NaI) but a weaker leaving group (chloride) compared to n-butyl bromide.
3. sec-butyl chloride: It has a stronger nucleophile (NaI) but more steric hindrance around the reaction center than n-butyl chloride.
4. benzyl chloride: It has a stronger nucleophile (NaI) than n-butyl chloride, but the benzyl group introduces more steric hindrance around the reaction center.
5. tert-butyl chloride: It has a stronger nucleophile (NaI) but high steric hindrance due to three methyl groups on the same carbon atom. This makes it the slowest reacting substrate.

Please note that this ranking is based on theory alone and assumes ideal reaction conditions. In practice, experimental results may vary.