# Gas-phase Curtius and Wolff rearrangement reactions investigated by tandem-MS, IR ion spectroscopy and theory

## TL;DR

This paper studies Curtius and Wolff rearrangement reactions in the gas phase using mass spectrometry and infrared spectroscopy, confirming theoretical predictions about their mechanisms.

## Contribution

The study provides experimental and theoretical evidence for the gas-phase Curtius and Wolff rearrangement mechanisms using tailored precursor ions and IR ion spectroscopy.

## Key findings

- Concerted N2-loss reactions produce isocyanates (Curtius) and ketenes (Wolff) as confirmed by IRIS and MS.
- Quantum-chemical calculations align with the observed reaction mechanisms and product structures.
- Tailor-made precursor ions with charge tags enable detailed analysis of reaction pathways.

## Abstract

The Curtius and the Wolff rearrangement reactions are investigated in the gas phase by tandem mass spectrometry (MS) and infrared ion spectroscopy (IRIS), probing the nature and intrinsic reactivity of three acyl azides and of one α-diazo keto analyte and that of their N2-loss products at temperatures around 300 K. Our study uses tailor-made precursor ions with innocent charge tags, which are activated upon collision-induced dissociation (CID). Our tandem-MS infrared ion spectroscopy (IRIS) study clearly evidences concerted N2-loss reactions delivering the ultimate reaction products of the Curtius reaction, i.e., the isocyanates, and the ones of the Wolff reaction, i.e., the ketenes. We show that this is fully consistent with the reaction mechanism predicted by quantum-chemical calculations. All IRIS data interpretation rests on computed linear IR spectra of ion structures identified by computational analysis based on DFT calculations with CCSD(T)-F12b energies.

The Curtius and the Wolff rearrangement reactions are investigated in the gas phase. Acyl azide and α-diazo keto analytes and respective N2-loss products are investigated by tandem mass spectrometry, infrared ion spectroscopy, and theory.