Microwave Spectrum, Structure, Quadrupole Interaction, Dipole Moment, and Bent C–Cl Bonds in 1,1-dichlorocyclopropane

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Abstract
The microwave spectrum of C3H4Cl235,35, C3H4Cl235,37, C3D4Cl235,35 C3D4Cl235,37, C3H3DCl235,35, C3H3DCl235,37 (cis and trans), and C2C13H4Cl235,35 have been investigated. Using the derived rotational constants, a complete structure for the molecule is calculated. The structural parameters are dC–H=1.085 A, dC(2)–C(3)=1.534 A, dC(1)–C(2)=1.532 A, dC–Cl=1.734 A, ∠H–C–H=117°35′, ∠C(2)–C(3)–H2=153°37′±15′, ∠Cl–C–Cl=114°38′. κ for C2C13H4Cl235,35 was very close to zero (±0.0001), and it was not possible to determine its sign unambiguously. Using the negative value instead of the more likely positive value, a slightly different structure was obtained. High‐resolution measurements were carried out on the Cl nuclear quadrupole hyperfine structure in order to obtain the complete quadrupole coupling constant tensor in the C3H4Cl235,35 principal inertial axis system. The values obtained are χaa=—43.545 Mc, χbb=4.100 Mc, χcc=39.445 Mc, all ±0.005 and χab=—51.5±0.3 Mc. The principal quadrupole‐coupling constant tensor elements are χα=—76.4±0.3 Mc, χβ=37.0±0.3 Mc, and χcc=39.445±0.005 Mc. The angle between the principal quadrupole axis component along the C–Cl bond and the C–Cl internuclear line is 0±15′. This is strong evidence against bent C–Cl bonds in this compound. Detailed analysis of the Stark effect in the presence of quadrupole interaction leads to a dipole moment of 1.58 debye.