T. K. Avirah

The microwave spectrum and conformation of 1,3‐cycloheptadiene

The microwave spectrum of 1,3‐cycloheptadiene has been studied. The ground state and a number of excited vibrational states have been assigned and the rotational constants evaluated. A study of the Stark effect has yielded the dipole moment components for the ground state and two of the excited vibrational states. The total dipole moment for the ground state is 0.740 D. These data have been used to determine the conformation of 1,3‐cycloheptadiene. The carbon skeleton is planar except for the C6 carbon atom (Cs form).

The microwave spectrum, dipole moment and ring planarity of 1,2-dimethylenecyclobutane

Abstract The microwave spectrum of 1,2-dimethylenecyclobutane has been studied in the range 26.5–40 GHz using a Hewlett-Packard 8400C Stark-modulated spectrometer. The rigid rotor constants have been derived for the ground state (in MHz: A = 4925.22, B = 4089.88, C = 2301.67) and four excited states of the ring-puckering vibration. That the ring skeleton is planar is indicated by the smooth variation of the rotational constants with vibrational state and by the value of 1/2(Ia + Ib − Ic) which is consistent with only 4 hydrogen atoms out of the plane of the remaining atoms. Analysis of the Stark effect yields a dipole moment lying along the b-axis; μb = 0.457 ± 0.002D. A physically reasonable set of structural parameters which reproduce the ground state rotational constants has been derived by adjustment of the carbon skeleton parameters by a diagnostic least-squares procedure.

The molecular conformation and dipole moment of 1,4-thioxane from the microwave spectrum

Abstract The microwave spectrum of 1,4-thioxane, a heterocyclic analogue of cyclohexane, has been studied in the region 26.5–40 GHz. The molecule is a highly asymmetric rotor ( k = −0.0740917). From the analysis of the a -type transitions, the rotational constants determined are (in MHz) A = 4333.85, B = 3076.14 and C = 1991.96. A study of the Stark effect has yielded the dipole moment components (in Debye units) μ a = 0.290 ± 0.003, gm c = 0.0537 ± 0.0004, which give a total dipole moment of μ = 0.295 ± 0.003. These data are consistent with a chair conformation for the ring.

The microwave spectrum and ring-puckering vibration of thietanone-3

Abstract The microwave spectrum of thietanone-3 has been studied in the R -band range (26.5–40.0 GHz) using a Hewlett-Packard Model 8400C phase stabilized Stark-modulated microwave spectrometer. The rotational constants in the ground state (in MHz: A = 10205.06 ± 0.59, B = 3266.63 ± 0.01, C = 2559.70 ± 0.01) and ten excited states of the ring-puckering vibration have been derived from fitting a -type low- J R -branch transitions. The rotational constants have been used in the determination of a single minimum anharmonic potential function for the ring-puckering vibration of the form V = a ( Z 4 + BZ 2 ) with a = 9.81, B = 6.41 where Z is a reduced ring-puckering coordinate. From the analysis of the Stark effect, the dipole moment has been determined in the ground vibrational state ( μ a = 0.999 ± 0.003D) and 5 excited states of the ring-puckering mode. This variation of the dipole moment is reproduced by the above potential function and the expansion μ v = 0.982 + 0.074〈 Z 2 〉 v , where 〈 Z 2 〉 v is the expectation value of Z 2 in the v th vibrational state. A model calculation to reproduce the variation of the rotational constants has been performed. There is some indication that the CCC (sp 2 ) and CSC ring angles decrease slightly as the ring puckers but the puckering is accomplished primarily by decreasing the CCS angles. A reasonable set of structural parameters which reproduce the ground state rotational constants has been derived by a diagnostic least-squares procedure.

The microwave spectrum and dipole moment of Δ6‐bicyclo[3.2.0]heptene

The rotational constants of Δ6‐bicyclo[3.2.0]heptene have been derived for the ground state (in MHz: A=4419.20, B=3080.16, C=2375.33) and several excited states of the low‐frequency vibrations of this molecule. The rotational constants were also derived for one monosubstituted 13C species in natural abundance. Stark effect measurements have yielded dipole moment components for the ground state of μa=0.201±0.001 D, μc=0.052±0.004 D, giving a total dipole moment of μ=0.208±0.001 D. These data are used to draw conclusions as to the conformation of this bicyclic compound.

The microwave spectrum, structure and centrifugal distortion constants of 2-chloroacrylonitrile

Abstract The microwave spectrum of 2-chloroacrylonitrile has been studied in the 26.5–40 GHz region. A total of 99 a- and b-type rotational transitions have been measured and assigned for CH 2 =C 35 Cl(CN),yielding values for the rotational constants (in MHz): A = 6973.27, B = 3148.16, C = 2165.95. For CH 2 =C 37 Cl(CN) a total of 53 transitions have been measured and assigned and the rotational constants obtained are (in MHz): A = 6909.35, B = 3081.17, C = 2127.98. The distortion effects have also been studied and the quartic distortion constants have been evaluated. From the observed hyperfine structure, the chlorine nuclear quadrupole coupling constants have been obtained. The structure of vinyl cyanide and vinyl chloride can be transferred to account remarkably well for the observed rotational constants.