MICROWAVE SPECTRUM AND CONFORMATION OF ISOPROPYL FLUOROFORMATE

Abstract

The microwave spectrum of isopropyl fluoroformate is characterized by intense a-type R branch transitions from one conformational species. The rotational constants of the ground state, $A_{0} = 4967.0(8) MHz, B_{0} = 1704.69(2) MHz, C_{0} = 1468.86(1) MHz$ are consistent with a $\tau(O=COC) ={0^\circ} , \tau(COCH) = {40^\circ}$ structure. This structure can be viewed as a combination of the two conformational species found in ethyl fluoroformate. Two vibrational satellites having rotational constants $A_{0} = 4963(5) MHz, B_{0}= 1694.11(7) MHz, C_{0}= 1471.43(4) MHz$ and $A_{0} 4998(6) MHz, B_{0} = 1705.21(7) MHz, C_{0} = 1471.10(4) MHz$ have been assigned. The spectra of both satellites show marked deviations from rigid rotor behavior. Ray’s asymmetry parameter, $\mu$, is very sensitive to rotation of the isopropyl group and the observed value, $\mu = - 0.865$, confirms that the conformation is asymmetrical and the methine C-H bond does not lie in the carboxyl group plane.