Vibrational spectra and conformations of alkyl substituted three‐membered ring compounds: Ethylcyclopropane, isopropylcyclopropane and ethyloxirane

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Abstract
The infrared spectra (from 4000 to 200 cm−1) and Raman spectra of ethylcyclopropane, isopropylcyclopropane and ethyloxirane have been recorded in solid, liquid and vapor phases. From the spectral data, ethylcyclopropane has been shown to exist solely in the gauche conformation in all three states of matter. Likewise, isopropylcyclopropane exists solely in a bisected conformation having a mirror plane of symmetry. On the other hand, however, in the gas phase ethyloxirane exists as an equilibrium mixture of the two nonequivalent gauche rotameric forms. In all cases, steric repulsions between methyl hydrogens and β‐ring hydrogens preclude the existence of possible conformers where a methyl group is situtated over (cis) the three‐membered ring. Tentative vibrational assignments have been proposed for major spectral bands of all three molecules.