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. N-acetyl-L-cysteine, an important antioxidant drug and a L-cysteine derivative, has been studied using rotational spectroscopy in the gas phase. Two conformers stabilized by different intermolecular interactions in a cis and trans dispositions have been detected. The barrier height of the methyl internal rotation is characterized for each conformer. image