Microscopic insights for effects of the alkyl chain length on macroscopic physical properties of 1-alkyl-3-methylimidazolium ionic liquids are provided from molecular dynamics computer simulation and quantum mechanical calculations. In particular, the liquid densities, internal energies, and hydrogen bonding behavior of the ions were studied. The effect of the alkyl chain size on the hydrogen bonding behavior of these liquids, in terms of both radial distribution functions and pair energetics, is demonstrated. Finally, studies of the ion pair stabilization were performed at the quantum mechanical level by means of the Kitaura-Morokuma energy partition. The fitting of atomic charges to the ion pairs has been performed to illustrate the charge transfer effect between cation and anion.