The effects of isomerism on the vibrational spectra and thermodynamic characteristics of biuret in the gas phase

Hydrogen-Bonding Modification in Biuret Under Pressure

“…In the literature, two different assignments are given for the two other, lower-frequency branches. The branch at 3270 cm −1 is assigned to motion by the N−H symmetric stretching bonds in the NH 2 groups and the branch at 3190 cm −1 to the stretching of the NH group by Korolevich et al 24 This assignment is reversed by Sullivan et al with the branch at 3270 cm −1 being assigned to the stretching of the NH group and that at 3190 cm −1 to the symmetric stretching of the NH 2 group. 26 This difference in the mode assignments does not affect the following analysis.…”

“…In the present study, the assignments of the modes have been taken from the literature. 24,26 In Figure 2, the ambient spectrum of biuret is shown along with the different types of vibrational motions approximately where they lie in vibrational frequency. To a very high degree of approximation, a true separation exists between the highfrequency N−H modes and all the other vibrational motions.…”

“…Additionally, many of the fundamental modes may have small Raman cross sections and scatter light weakly. In the present study, the assignments of the modes have been taken from the literature. , …”

“…30 The cis (trans) denotes that the CO groups are on the same side (opposite sides) of the molecule (see Figure 1). Based upon the infrared gas spectra and theoretical calculations, it has been suggested that isolated molecules of biuret exist as a mixture with a 3:2 of trans to cis in equilibrium at 400 K. 24 It is possible that a mixture of both isomers might exist in the crystal.…”