Knowledge Bank

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, $A0=4967.0(8)MHz,B0=1704.69(2)MHz,C0=1468.86(1)MHz$ 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 $A0=4963(5)MHz,B0=1694.11(7)MHz,C0=1471.43(4)MHz$ and $A04998(6)MHz,B0=1705.21(7)MHz,C0=1471.10(4)MHz$ 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.