Impact of the Acetyl Group on Cysteine: A Study of N‐Acetyl‐Cysteine through Rotational Spectroscopy

Herein, we report a spectroscopic study of N‐acetyl‐L‐cysteine, an important antioxidant drug, using Fourier‐transform microwave techniques and in isolated conditions. Two conformers are observed, where most stable structure adopts a cis disposition, and the second conformer has a lower abundance and adopts a trans disposition. The rotational constants and the barriers to methyl internal rotation are determined for each conformer, allowing a precise conformation identification. The results show that the cis form adopts an identical structure in the crystal, solution, and gas phases. Additionally, the structures are contrasted against those of cysteine.