RESUMO
<p><b>AIM</b>To study the NMR phenomena of cetirizine hydrochloride and assign all proton and carbon signals in NMR spectra.</p><p><b>METHODS</b>To record the 1D and 2D NMR spectra of cetirizine hydrochloride while changing the experimental temperature and adding D2O into the solution.</p><p><b>RESULTS</b>More than one NMR signal or broad peak resulting from piperazine and the attached groups with N atom were given in DMSO-d6 solution at room temperature. "Coalescence" or narrowing had occurred for the proton and carbon signals when the experimental temperature was increased or D2O was added into the solution.</p><p><b>CONCLUSION</b>Compared with the NMR "time scale", there are more than one conformation of cetirizine hydrochloride in DMSO-d6 solution at room temperature. The different conformation will be exchanged fast while temperature rise and the stable conformation will be existed while D2O was added into the solution.</p>