Theory Study of Different Substituent Length on Structure Property of N-methyl Morpholinium Ionic Liquid

By using at density functional theory (DFT) at B3LYP/6-31G* levels, The morpholinium ionic liquid with different substituent length have been studied. The computed results indicate that the ionic liquid formed by N-methyl ethyl morpholinium and a bromine ion has three structure (mon, nop, orth) and six position. Three hydrogen bond have been formed in each position, The hydrogen bond between chlorine ion and hydrogen atom in morpholinium ring is strongest and shortest. The hydrogen bond between bromine ion and hydrogen atom in methyl or ethyl is weaker, which can strengthen the stability of ion pair. For N-methyl ethyl morpholinium, N-methyl propyl morpholinium and N-methyl butyl morpholinium, as the alkyl length becomes longer, the hydrogen bond length between bromine ion and hydrogen atom in morpholinium ring becomes longer, the binding energy between bromine ion and morpholinium with different alkyl length becomes weaker.