Anions are always considered to explain most of the cellulose dissolution in the ionic liquid; where electron donor theory is always used to elaborate cellulose dissolution in the ionic liquids with different anions. However, the theory does not apply to ionic liquids with different alkyl chain anions. Herein, the hydrogen bond theory was proposed to further explain cellulose dissolution by density functional theory (DFT) calculations. 1-allyl-3-methylimidazole carboxylate ionic liquids with different alkyl chains including ([Amim][HCOO], [Amim][CH₃COO], [Amim][CH₃CH₂COO], [Amim][CH₃CH₂CH₂COO]) were investigated. The DFT results indicated that the alkyl chains of the anions directly affect the hydrogen bond and the interaction energy between the cations and anions; where the length of the hydrogen bonds between cation and anion is the most predominant factor for determining the polarity parameter β value of the ionic liquid itself and therefore governing cellulose dissolution. Moreover, a shorter length of hydrogen bonds between the anions of ionic liquid and cellobiose referred to a better solubility of cellulose in the ionic liquids.

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