Microwave spectra and structure of 1,2-dichlorobenzene-3 d and -4 d

Abstract

The microwave spectra of six monodeuterated 1,2-dichlorobenzenes-3 d and -4 d, each having 1,2- 35Cl 2, 1,2- 35Cl 37Cl, or 1,2- 37Cl 35Cl, in the frequency range 10–40 GHz, have been analyzed. The r 0-structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r 0 bond lengths (Å) and bond angles (degrees) are as follows: r CC = 1.393–1.398; r CH = 1.080–1.083; r CCl = 1.729(15); ∠CCC = 119.5–120.3; ∠C(1)C(2)Cl(2) = 120.9(5); ∠C(2)C(3)H(3) = 118.7(11); and ∠C(3)C(4)H(4) = 119.5(13). The following distortions in the structure are found. The distortion of the benzene ring is of the same extent as in chlorobenzene and rather smaller than in fluorobenzenes. On the other hand, the two CCl bonds bend outwards from each other by about 1° and the ortho-hydrogen H(3) by 0.6° towards the Cl atom, respectively, from the bisector at the ipso-carbon. The ortho-hydrogen is closer to the chlorine atom. The possibility of a “bent bond” in the CCl has been inspected from the nuclear quadrupole coupling constants of chlorine nuclei.