Knowledge Bank

The microwave spectrum of $CH3CHF35$ Cl has been assigned up to J = 60; the rotational constants and centrifugal distortion constants are (in MHz): A = 9016.13, B = 4666.67, C = 3329.37, $\Delta J$ = - 0.0020967, $\Delta JK$ = 0.0030325, $\Delta K$ = 0.0059960, $\delta J$ = 0.00043553, $\delta K$ = 0.0038657. The quadrupole coupling constants are (in MHz): $Xaa=-62.26,Xab=34.18,Xcc=28.08$. The $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl$ isotope has rotational constants A = 9015.23, B = 4538.24, C = 3262.81 MHz. Assuming the same methyl group as $CH3CH2Cl$, a partial structure is C $-$ C = 1.529 \AA, C $-$ Cl = 1.731 \AA, C - F = 1.399 \AA, $\Delta$ CCCl = $111.27\circ$, $\Delta$ CCF = $106.99\circ$. The relative intensity of the V = 1 excited torsional state of the $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl isotope indicates a barrier to internal torsion of 3.9 $\perp$ 0.3 kcal/mole.