C4Cl2O2
	Chlorine
	Nuclear Quadrupole Coupling Constants
		in1,2-Dichlorocyclobuten-3,4-dione
	Chlorine nqcc tensors in 1,2-dichlorocyclobuten-3,4-dione (C4Cl2O2) were calculated here on an ropt molecular structure given by B3LYP/cc-pVTZ optimization.  These calculated nqcc's are given in Tables 1 - 3.  Structure parameters are given in Table 4.
	In Tables 1 - 3, subscripts a,b,c refer to the principal axes of the inertia tensor, subscripts x,y,z to the principal axes of the nqcc tensor.  ETA = (Xxx - Xyy)/Xzz.  Ø (degrees) is the angle between its subscripted parameters.
	RSD is the calibration residual standard deviation for the B1LYP/TZV(3df,2p) model for calculation of the efg's/nqcc's.
	Table 1.  Chlorine nqcc's in 35-35 species of C4Cl2O2 (MHz).  Calculation was made on the B3LYP/cc-pVTZ ropt structure.     Calc Expt     35Cl Xaa - 10.82 Xbb - 17.94 Xcc 28.76 Xab ± 59.62   RSD 0.49 (1.1 %)     Xxx 45.35 Xyy 28.76 Xzz - 74.11 ETA - 0.224 Øz,a 46.71 Øa,CCl 46.67 Øz,CCl   0.04
	Table 2.  Chlorine nqcc's in 35-37 species of C4Cl2O2 (MHz).  Calculation was made on the B3LYP/cc-pVTZ ropt structure.     Calc Expt     35Cl Xaa   7.90 Xbb - 36.66 Xcc 28.76 Xab +/- 55.42     RSD 0.49 (1.1 %)     37Cl Xaa - 23.57 Xbb   0.91 Xcc 22.67 Xab -/+ 45.46   RSD 0.44 (1.1 %)
	Table 3.  Chlorine nqcc's in 37-37 species of C4Cl2O2 (MHz).  Calculation was made on the B3LYP/cc-pVTZ ropt structure.     Calc Expt     37Cl Xaa - 8.53 Xbb - 14.14 Xcc 22.67 Xab ± 46.99   RSD 0.44 (1.1 %)
	Table 4.  1,2-Dichlorocyclobuten-3,4-dione.  Molecular structure parameters, ropt (Å and degrees).  These are compared with "plausible" ro structure parameters of Ref. [1].   ropt    ro C=O 1.1889 1.1906 C=C 1.3609 1.3478 C(2)-C(3) 1.5060 1.5133 C(3)-C(4) 1.5721 1.5689 C-Cl 1.6855 1.6813 C=C-C   94.02   94.19 C=C-Cl 133.33 133.27 C(2)-C(3)=O 135.91 135.45
	[1] W.Caminati, A.C.Fantoni, B.Lunelli, and F.Scappini, J.Mol.Spectrosc. 131,154(1988).
	1,2-Dichloroperfluorocyclobutene				1,2-Dichloroperfluorocyclohexene
	1,2-Dichloroperfluorocyclopentene
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	Molecules/Chlorine
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