Nitrene Chemistry: Key Examples of Aziridine Formation and Rearrangements

📚 Quick Study Guide

• 🔥 Nitrenes: These are highly reactive, uncharged, monovalent nitrogen species. They possess six valence electrons and are isoelectronic with carbenes.
• 🧪 Aziridine Formation: Nitrenes can add to alkenes to form aziridines, which are three-membered nitrogen-containing rings. This is a valuable reaction in organic synthesis.
• ⚗️ Mechanism: Typically involves a concerted or stepwise addition of the nitrene to the alkene \(\pi\) bond.
• 💡 Singlet vs. Triplet Nitrenes: Singlet nitrenes tend to add stereospecifically (concerted), while triplet nitrenes undergo stepwise addition, leading to loss of stereochemistry.
• 🔄 Rearrangements: Nitrenes undergo various rearrangements, including Wolff rearrangements (similar to carbenes) and C-H insertion reactions.
• 🌡️ Reaction Conditions: The formation and reactions of nitrenes are often carried out under photolytic or thermal conditions.
• 🔑 Key Reagents: Common precursors for nitrenes include azides (\(R-N_3\)) which decompose to release nitrogen gas and generate the nitrene.

Practice Quiz

1. Which of the following is a key characteristic of nitrenes?
   1. A) They are positively charged.
   2. B) They have eight valence electrons.
   3. C) They are uncharged and have six valence electrons.
   4. D) They are stable and unreactive.
2. What type of ring is formed when a nitrene adds to an alkene?
   1. A) Oxirane
   2. B) Aziridine
   3. C) Cyclobutane
   4. D) Epoxide
3. What is a common precursor used to generate nitrenes?
   1. A) Alcohols
   2. B) Ethers
   3. C) Azides
   4. D) Ketones
4. Which type of nitrene typically adds to alkenes stereospecifically?
   1. A) Triplet nitrene
   2. B) Singlet nitrene
   3. C) Both singlet and triplet nitrenes
   4. D) Neither singlet nor triplet nitrenes
5. What type of rearrangement is commonly associated with nitrenes?
   1. A) Diels-Alder reaction
   2. B) Wolff rearrangement
   3. C) Grignard reaction
   4. D) Wittig reaction
6. Under what conditions are nitrene reactions often carried out?
   1. A) Acidic conditions
   2. B) Basic conditions
   3. C) Photolytic or thermal conditions
   4. D) High pressure conditions
7. What is the key difference in the mechanism of addition between singlet and triplet nitrenes to alkenes?
   1. A) Singlet nitrenes undergo stepwise addition, while triplet nitrenes undergo concerted addition.
   2. B) Singlet nitrenes undergo concerted addition, while triplet nitrenes undergo stepwise addition.
   3. C) Both undergo concerted addition.
   4. D) Both undergo stepwise addition.