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Abstract The knowledge of viscosity about ionic liquids is important for their large scale-up application. Although some theoretical models and experimental methods are developed to evaluate the viscosity, there are some common disadvantages for them including complexity, time consuming, and unreliable. It is necessary to develop a simple method to evaluate the viscosity. Even if the accurate value of viscosity could not be obtained, the relative sequence for a series of ionic liquids with similar structures is still beneficial for their applications. The relationship between hydrogen bond and viscosity for TBA pyruvate, TBA L‐lactate, and TBA L‐malate are studied by combination of molecular dynamics simulation and quantum chemistry methods. The strength of hydrogen bond in TBA L‐malate is the larger resulting in the larger viscosity. In contrast, the number of hydrogen bond has a minor influence on the viscosity. It is expected that this study would provide some useful information to build the relationship between hydrogen bond and viscosity for task functionalized ionic liquids. Graphical abstract Unlabelled Image Highlights • Relationship between hydrogen bond and viscosity • The inclusion of hydroxyl group is helpful to improve the strength of hydrogen bonds. • Strength of hydrogen bonds is determined items for viscosity rather than the number. [ABSTRACT FROM AUTHOR]

The excellent catalytic activity of [N 2,2,2,2OH ][SA] is traced to the critical role played by nucleophilic-electrophilic dual activation from [SA]- anions in the cycloaddition reaction of CO 2. [Display omitted] • The catalytic mechanism of carboxylate anion-based ionic liquids is firstly elucidated in this work. • The catalytic role of carboxylate anions is complex and flexible. • The underlying electrophilic activation ability of the carboxylic acid anion plays a critical role in enhancing the catalytic activity. • The electrophilic activation plays a more important role than nucleophilic activation in the ring-opening step. Elucidating the mechanism of carbon dioxide (CO 2) cycloaddition reaction catalyzed by ionic liquid (ILs) facilitates the rational design of efficient IL catalysts at the molecular level. To date, a great deal of research has been devoted to the halogen-containing ILs, however, the catalytic mechanism of halogen-free ILs remains unclear. In this contribution, an exhaustive theoretical study of the coupling reaction of CO 2 with epichlorohydrin (ECH) catalyzed by three halogen-free ILs has been carried out for the first time by combining density functional theory (DFT) calculations with molecular dynamics (MD) simulations. Meanwhile, the effect of carboxylate anion structure on catalytic activity is deeply investigated. The final results provide a comprehensive catalytic mechanism of carboxylate anion-based ILs. The most favorable mechanism involves three steps, i.e., ring-opening of ECH, CO 2 insertion, and ring-closure to form the product. Among them, the ring-opening of ECH is the rate-determining step (RDS). Additionally, the analytical results of the independent gradient model based on Hirshfeld partition (IGMH) and atoms in molecules (AIM) suggest that the electrophilic activation from carboxylate anions plays a critical role in promoting the ECH ring-opening process. The electrophilic activation of anions is investigated for the first time in this work. The results indicate that incorporating electrophilic groups into anions is a promising pathway to develop new robust and efficient halogen-free ILs. [ABSTRACT FROM AUTHOR]