The paracetamol-water (PA-H 2 O) complexes formed by hydrogen bonding interactions were investigated at the MP2/6-311++G(d,p) level. Six PA-H 2 O complexes possessing various types of hydrogen bonds (H-bonds) were characterized by geometries, energies, vibrational frequencies. Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) and the localized molecular orbital energy decomposition analysis (LMO-EDA) were performed to explore the nature of the hydrogen-bonding

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... in these complexes. The intramolecular H-bond formed between the methylene and carbonyl oxygen atom of paracetamol is retained in most of complexes. The H-bonds in PW1 and PW6 are stronger than other H-bonds, moreover, the researches show that both the hydrogen bonding interaction and structural deformation play important roles for the relative stabilities of PA-H 2 O complexes. Keyword: paracetamol; hydrogen bonding interactions; natural bond orbital (NBO); quantum theory of atoms in molecules (QTAIM)