Quiz - SN Reactions I | Alkyl Halides - Nucleophilic Substitutions

Organic Chemistry 1 - Quiz - SN Reactions I


What is a unimolecular nucleophilic substitution (SN1)?

SN1 reactions are nucleophilic substitutions that proceed through a carbocation intermediate ⇒ SN1 reactions are unimolecular with a bond-breaking step followed by a bond-making step


What is the specific rotation of the alcohol produced in the bimolecular nucleophilic process shown below?

A bimolecular nucleophilic process and NaOH, a strong nucleophile, mean that the reaction is a SN2. A SN2 is a one-step process with inversion of configuration. The alcohol produced is the enantiomer (mirror image) of the alcohol drawn with a specific rotation of -5.6. The correct answer is therefore [α]D = +5.6


What is the specific rotation of the alcohol produced in the following nucleophilic substitution?

The tertiary alkyl halide and the poor nucleophile (H2O) mean that the reaction is an SN1. In an SN1 process, the leaving group leaves, forming a carbocation, and then the nucleophile attacks the carbocation to give the product. Because of the planar carbocation intermediate, SN1 reactions result in a racemization of the stereochemistry in the reaction center (nucleophiles can attack from both sides). Therefore, the specific rotation of the mixture is [α]D = 0.0


What reagent could accomplish this reaction:   


According to the reaction, the nucleophile is N3-. The only possible reactants are IN3 and NaN3. The electronegativity of Na is 0.93, that of I is 2.66 and that of N is 3.04. The difference in electronegativity is greater between Na and N3 than between I and N3, which makes NaN3 the best reagent for this reaction


What is the transition state of the reaction of CH3I with CH3OK in CH3OH?

CH3I is a primary alkyl halide and CH3OK is a strong nucleophile. The reaction is an SN2, a bimolecular with simultaneous bond-making and bond-breaking steps:


Which factor affects the SN1 and SN2 reactions the most?

The nature of the alkyl halide is the most important factor in determining whether a reaction follows the SN1 or SN2 mechanism:

  • Methyl halides (CH3X) and primary halides (RCH2X) ⇒ SN2 reactions only
  • Tertiary halides (R3CX) ⇒ SN1 reactions only
  • Secondary halides (R2CHX) ⇒ both SN1 and SN2 reactions. Other factors such as the strength of the nucleophile and the polarity of the solvent determine the mechanism