Organic chemistryLesson 1 of 2 in the course Nucleophilic substitution and elimination

Nucleophilic Substitution: SN1, SN2, and Related Pathways

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

Nucleophilic substitution is a fundamental reaction type in organic chemistry: an electron-rich species replaces a group attached to an electron-deficient atom. This lesson introduces the general reaction and compares the two main mechanisms at saturated carbon, SN2 and SN1.

Nuc:+R−LG→R−Nuc+LG:\mathrm{Nuc: + R-LG \rightarrow R-Nuc + LG:}

OH−+R−Br→R−OH+Br−\mathrm{OH^- + R-Br \rightarrow R-OH + Br^-}

All flashcards

What is a nucleophile?
An electron-rich species that donates an electron pair to form a bond.
What is the SN2 rate law?
Rate=k[Sub][Nuc]\mathrm{Rate}=k[\mathrm{Sub}][\mathrm{Nuc}]; the rate depends on substrate and nucleophile concentrations.
What stereochemical outcome can occur in an SN1 reaction?
Attack on a planar carbocation from either face can produce a mixture of configurations.
What characterizes the SNi mechanism?
The nucleophile is delivered from the same side as the leaving group.
How does substitution at a carbonyl center commonly proceed?
A nucleophile adds first, then a leaving group departs as the carbonyl reforms.

Quiz questions

  1. Which description best characterizes an SN2 reaction?Answer: Bond formation and leaving-group departure occur together in one concerted step.
  2. What is the rate equation for an SN2 reaction?Answer: Rate=k[Sub][Nuc]\mathrm{Rate}=k[\mathrm{Sub}][\mathrm{Nuc}]
  3. Why is backside attack important in an SN2 reaction at a stereogenic carbon?Answer: It leads to inversion of the arrangement at that carbon as the new bond forms.
  4. For a typical SN1 reaction, which concentration directly appears in the rate law?Answer: The substrate concentration
  5. How does substitution at a carbonyl carbon commonly occur?Answer: Nucleophilic addition followed by elimination that restores the carbonyl

Based on the Wikipedia article Nucleophilic substitution, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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