Infrared spectroscopy of 2-pyrrolidinone and its hydrogen bonded dimers in a cold (8 K) inert gas matrix

Matrix isolation-FTIR spectra of 2-pyrrolidinone monomer and its two hydrogen bonded dimers are recorded in N₂ matrix at 8 K temperature and in CCl₄ solution at variable temperature within the range 30-45 °C. The transient singly hydrogen bonded dimer (SHBD) is identified in the cold N₂ by comparing the matrix spectrum with that in CCl₄ solution. The spectral shifts of both amide-I and amide-A bands indicate cooperative strengthening of hydrogen bonds in doubly hydrogen bonded dimer (DHBD). Density functional theory at B3PW91/6-311++G** level of calculation is found to be in good accord to the observed spectral features.