Conformation Composition Effect on the Raman Spectrum of Linear Trimer of Ethylene Glycol

Raman spectroscopy and density functional theory were used to investigate the conformation composition of the linear trimer of ethylene glycol (TEG). The Raman spectra of liquid ethylene glycol oligomers (trimer, tetramer, nonamer) and ethylene glycol were recorded at an excitation wavelength of 532 nm. The observed differences in the Raman spectra of the oligomers compared to ethylene glycol are due to their richer conformation composition. In the experimental sample, all three O–CH2–CH2–O fragments of the TEG molecule mainly occur in gauche-conformations (G, G'), but the formation of significant quantities of forms with one terminal fragment O–CH2–CH2–O in trans-conformation (T) is also possible. It has been shown that the formation of intramolecular OH…O hydrogen bonds competes with the formation of intermolecular bonds of the same type; therefore, the number of intramolecular bonds does not exceed one per TEG molecule. The conformation composition and intramolecular hydrogen bonds have a decisive effect on the appearance of the Raman spectrum of TEG, and in the spectral range from 700 to 1600 cm–1 the corresponding effects are the most pronounced.