# Pyrrole without Life: Reaction of Aminomethylene with the Propargyl Radical

## TL;DR

Scientists discovered a new way to form pyrrole, a key nitrogen-containing ring, through reactions in gas-phase environments.

## Contribution

The study reveals a barrierless, orientation-dependent mechanism for pyrrole formation from aminomethylene and propargyl radical.

## Key findings

- The reaction of aminomethylene with propargyl radical forms pyrrole + H via an addition–elimination mechanism.
- The allenyl resonance form of propargyl is crucial for pyrrole formation.
- This pathway offers a selective route to nitrogen-containing aromatics in gas-phase chemistry.

## Abstract

Carbenes are reactive
species found across gas-phase
environments,
from combustion to planetary atmospheres and interstellar space. Their
reactions with radicals represent a compelling path to increasing
chemical complexity, in which the formation of the first aromatic
ring is a foundational step. To date, no selective gas-phase bottom-up
route to the smallest nitrogen-bearing aromatic ring, pyrrole, is
known. We investigated the reaction of the simplest aminocarbene,
aminomethylene, with the prototypical resonance stabilized propargyl
radical. Photoelectron photoion coincidence spectroscopy and semiautomated
electronic structure calculations reveal a barrierless, addition–elimination
mechanism producing pyrrole + H. The reaction path depends on the
orientation of propargyl during the association, in which the allenyl
resonance form (H2CCCH•) of propargyl leads to pyrrole formation. This selective pathway
highlights the promise of radical chemistry to fill important gaps
in chemical reaction networks.