Quantitative study on hydrogen bonding between urethane compound and ethers by infrared spectroscopy

A quantitative infrared spectroscopic study of a model urethane‐type compound was carried out in order to obtain basic data on hydrogen bonding in polyurethanes. First, the absolute intensity of free NH groups of N‐phenylurethane, which was adopted as the model urethane, was determined by Wilson‐Wells' method to be 3.59 × 103l./mole‐cm.2. The free NH of this urethane absorbed at 3447 cm.−1, and hydrogen‐bonded NH absorbed near 3300 cm.−1. Then, the extents of hydrogen bonding of the urethane at various concentrations were determined, and the hydrogen bonding between the urethane and ethers was studied by using the above‐mentioned absolute intensity. For comparison, diphenylamine was also used as proton donor. Di‐n‐butyl ether and poly‐(oxyethylene glycol) were examined and proved to be able to act as proton acceptors. The frequency shifts of NH stretching vibration of diphenylamine and N‐phenylurethane caused by hydrogen bonding with di‐n‐butyl ether were 96 cm.−1 and 150 cm.−1, respectively. The equilibrium constants were 4.8 × 10−1l./mole for the former system 4.6 × 10−1l./mole for the latter.