Microwave Spectra, Dipole Moments, and Torsional Potential Constants of cis- and trans-Cyclopropanecarboxylic Acid Fluoride

Microwave spectra have been assigned for the ground state and several excited torsional states of species of cyclopropanecarboxylic acid fluoride with the oxygen atom cis and trans to the cyclopropane ring. Dipole moments obtained by analysis of the Stark effect are as follows: trans species: ${\mu }_a\text{\hspace{0.17em}=\hspace{0.17em}3.43\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{D}{\mathrm{,\; \mu }}_b\text{\hspace{0.17em}=\hspace{0.17em}0.44\hspace{0.17em}±\hspace{0.17em}0.05}\mathrm{D}{\mathrm{,\; \mu }}_c\text{\hspace{0.17em}=\hspace{0.17em}0, μ\hspace{0.17em}=\hspace{0.17em}3.46\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{D}$ ; cis species: ${\mu }_a\text{\hspace{0.17em}=\hspace{0.17em}2.85\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{D}{\mathrm{,\; \mu }}_b\text{\hspace{0.17em}=\hspace{0.17em}1.63\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{D}{\mathrm{,\; \mu }}_c\text{\hspace{0.17em}=\hspace{0.17em}0, μ\hspace{0.17em}=\hspace{0.17em}3.28\hspace{0.17em}±\hspace{0.17em}0.03}\mathrm{D}$ . By analysis of estimates of the torsional excitation energies of the two species and the cis–trans energy difference, values of the first three coefficients of a Fourier expansion of the torsional potential have been obtained as follows: $V_1\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}1520\hspace{0.17em}±\hspace{0.17em}320}\mathrm{cal}/\mathrm{mole}{\mathrm{,\; V}}_2\text{\hspace{0.17em}=\hspace{0.17em}5150\hspace{0.17em}±\hspace{0.17em}700}\mathrm{cal}/\mathrm{mole}{\mathrm{,\; V}}_3\text{\hspace{0.17em}=\hspace{0.17em}990\hspace{0.17em}±\hspace{0.17em}260}\mathrm{cal}/\mathrm{mole}$ .