The microwave spectrum of propionaldehyde, CH3CH2CHO, has been investigated in the frequency region 8–38 Gc/sec. The existence of two stable rotamers has been demonstrated. The cis rotamer, in which the four heavy atoms are coplanar, is more stable by 900±100 cal/mole. An approximate treatment of the coupling of the —CH3 and C–C torsional motions in the cis rotamer is presented. Using this treatment the barrier to internal rotation in the cis rotamer is found to be 2280±110 cal/mole. The dihedral angle in the higher energy, gauche rotamer is about 131°. Evidence is given for coupling of the C–C torsional momentum and over-all rotational angular momentum in the gauche rotamer. Other aspects of the spectrum are also discussed.
Tbe microwav~ sp~ctrum. of 1,3, 5-cycloheptatriene has been investigated in the frequency region 17-35 Gc/s~c. A quantItatIve estImate of the nonplanarity of the ring has been made using the ground-state rotatlOnal constants of the normal isotopic ~peci~s. The components of the total dipole moment are Jl.a= 0.24±0.04 D and Jl.,=0.060±0.002 D. The VlbratlOnal satellites and other aspects of the microwave spectra of molecules of this type are discussed.
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