Chlorobenzene

C₆H₅Cl

Chlorine

Nuclear Quadrupole Coupling Constants

in Chlorobenzene

Measurement of the chlorine nqcc's in chlorobenzene was most recently made by Merke et al. [1]. Earlier measurements were made by Caminati and Mirri [2], Poynter [3], and Selén [4]. A substitution molecular structure was reported by Michel et al. [5]. Cradock et al. [6] report a structure determined by combined analysis of electron diffraction, rotation constant, and liquid crystal NMR data.

Chlorine nqcc's were calculated here on the molecular structures of Michel et al. and Cradock et al., and on a structure derived by B3P86/6-31G(3d,3p) optimization. These calculated nqcc's are compared with the experimental values in Tables 1-3. The structure parameters are compared in Table 4. In Table 5, atomic coordinates for the optimized structure are given.

In Tables 1-3, RMS is the root mean square difference between calculated and experimental nqcc's (percentage of the average of the magnitudes of the experimental nqcc's). RSD is the calibration residual standard deviation for the B1LYP/TZV(3df,2p) model for calculation of the nqcc's.


Table 1. Chlorine nqcc's in C₆H₅Cl (MHz). Calculation was made on the substitution structure of Michel et al. [5].

			Calc.		Expt. [1,3]

³⁵Cl	X_aa	-	71.64	-	71.241(7) [1]
	X_bb		39.00		38.237(10)
	X_cc		32.64		33.005(10)
	ETA *	-	0.089	-	0.073

	RMS		0.54 (1.1 %)
	RSD		0.49 (1.1 %)

³⁷Cl	X_aa	-	56.46	-	56.10(50) [3]
	X_bb		30.74
	X_cc		25.72

* ETA = (X_bb - X_cc)/X_aa = (X_xx - X_yy)/X_zz.


Table 2. Chlorine nqcc's in C₆H₅Cl (MHz). Calculation was made on the r^o_alpha structure of Cradock et al. [6].

			Calc.		Expt. [1,3]

³⁵Cl	X_aa	-	71.90	-	71.241(7) [1]
	X_bb		38.93		38.237(10)
	X_cc		32.96		33.005(10)
	ETA *	-	0.083	-	0.073

	RMS		0.55 (1.2 %)
	RSD		0.49 (1.1 %)

³⁷Cl	X_aa	-	56.66	-	56.10(50) [3]
	X_bb		30.68
	X_cc		25.98

* ETA = (X_bb - X_cc)/X_aa = (X_xx - X_yy)/X_zz.


Table 3. Chlorine nqcc's in C₆H₅Cl (MHz). Calculation was made on the B3P86/6-31G(3d,3p) r_opt structure.

			Calc.		Expt. [1,3]

³⁵Cl	X_aa	-	71.75	-	71.241(7) [1]
	X_bb		38.91		38.237(10)
	X_cc		32.84		33.005(10)
	ETA *	-	0.084	-	0.073

	RMS		0.50 (1.0 %)
	RSD		0.49 (1.1 %)

³⁷Cl	X_aa	-	56.55	-	56.10(50) [3]
	X_bb		30.67
	X_cc		25.88

* ETA = (X_bb - X_cc)/X_aa = (X_xx - X_yy)/X_zz.


Table 3. Molecular structure parameters (Å and degrees).

		r_s[5]	r^o_alpha[6]	r_opt

	C(1)Cl	1.7248	1.7390	1.7364
	C(1)C(2)	1.399	1.3908	1.3895
	C(2)C(3)	1.386	1.3942	1.3900
	C(3)C(4)	1.3976	1.4000	1.3903
	C(2)H(2)	1.080	1.0779	1.0833
	C(3)H(3)	1.081	1.0872	1.0848
	C(4)H(4)	1.081	1.0795	1.0843
	C(6)C(1)C(2)	120.16	121.65	121.30
	C(1)C(2)C(3)	119.78	119.05	119.00
	C(2)C(3)C(4)	120.24	120.24	120.47
	C(3)C(4)C(5)	119.80	119.79	119.77
	C(1)C(2)H(2)	119.45	119.67	119.87
	C(2)C(3)H(3)	119.76	120.41	119.33

	For comparison with r_opt, the B3P86/6-31G(3d,3p) optimized structure of benzene is CC = 1.3909 Å and CH = 1.0851 Å.


Table 4. Atomic coordinates, B3P86/6-31G(3d,3p) r_opt
(More figures are shown than are significant.)

			a (Å)		b (Å)

	Cl		2.164557		0.0
	C(1)		0.428114		0.0
	C(2,6)	-	0.252998	±	1.211162
	C(3,5)	-	1.642982	±	1.202605
	C(4)	-	2.340584		0.0
	H(2,6)		0.301360	±	2.141916
	H(3,5)	-	2.180249	±	2.145010
	H(4)	-	3.424922		0.0