Aqueous solutions of five ionic liquids (ILs) of the 1-n-alkyl-3-methylimidazolium bromide family, [C(n)mim]Br (n = 4, 6, 8, 10, 12), were investigated by NMR measurements at 298.2 K as a function of IL concentrations. Critical aggregation concentrations and aggregation numbers of these ILs were determined by 1H NMR except for [C4mim]Br in D2O. The effects of the alkyl chain length of the cations were examined on the aggregation behavior of the ILs. 1H NMR data of the solvent D2O were used to investigate the hydration of the ILs in D2O, and it was found that the ionic hydration and the cation-anion association or aggregation of the ILs offset each other. The microenvironment of different protons of cations of the ILs in the aggregates was probed by determining the spin-lattice relaxation rate (1/T1). It is suggested that the imidazolium rings in the aggregates are exposed to water and that the molecular motion of the aggregates is more restricted than that of the monomers of the ILs. Furthermore, a stair-like microscopic aggregation structure is suggested for the [C(n)mim]Br/D2O (n = 6, 8, 10) systems from 2-D 1H-1H NOESY measurements.

The infrared spectrum (IR) characteristic peaks of amide I, amide II, and amide III bands are marked as amide or peptide characteristic peaks. Through the nuclear magnetic resonance study, N-methylacetamide has been determined to have six fine components, which include protonation, hydration, and hydroxy structures. Then the independent IR spectrum of every component in Nmethylacetamide is calculated by using the density functional theory quantum chemistry method, and the contribution of each component to amide I, II, and III bands is analyzed. The results of this research can help to explain the formation of the amide infrared spectrum, which has positive significance in organic chemistry, analytical chemistry, and chemical biology.

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Summary 1H and 13C NMR chemical shifts have been determined to investigate the interactions of acetone with room temperature ionic liquids ([C4mim][PF6], [C6mim][PF6], [C8mim][PF6] and [C6mim][BF4]) at various acetone mole fractions. Changes in the chemical shifts of hydrogen and carbon atoms of the above systems indicated that hydrogen bonds were formed between the ring protons, the methyl and methylene next to the nitrogen of the ionic liquids and the carbonyl oxygen of the acetone molecules. The strength of hydrogen bond was found to be influenced not only by the type of the anion but also by the length of alkyl chain on the imidazolium ring of cations. At the same time, ab initio calculations have been performed to support the NMR results.