The results of nonempirical calculations (6-31G* basis), IR spectra, and di
pole moments (253-323 K) show that 1-ethyl-2-formylimidazole in the gas pha
se prefers the synperiplanar form, while in nonpolar and weakly polar solve
nts, antiperiplanar. Polar media stabilize the antiperiplanar conformer wit
h a high dipole moment. Solvatochromism is shown to be useful for qualitati
ve conformational analysis of this compound. The dependence of the long-wav
e absorption maximum in the UV spectra of the title compound on solvent pol
arity (Kamlet-Taft pi* parameter) is described by two correlation equations
for different conformers. The most solvent-sensitive is the absorption ban
d of the antiperiplanar conformer.