1-Chloro-1,1,2-Fluoroethane

ClF₂C-CH₂F

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Chlorine

Nuclear Quadrupole Coupling Constants

in trans-1-Chloro-1,1,2-Trifluoroethane

Calculation of the chlorine nqcc's in trans-1-chloro-1,1,2-trifluoroethane was made on structures with bond lengths derived ab initio by the methods of the Lille group, as described below. Interatomic angles used are those given by (1) MP2/6-311+G(d,p), and (2) B3P86/6-311+G(3d,3p) optimization. Calculated nqcc's are compared with the experimental nqcc's of Liu et al. [1] in Tables 1 and 2. Structure parameters are given in Z-Matrix format in Table 3.

The results of calculations made on MP2/aug-cc-pVTZ approximate equilibrium structures of both trans and gauche conformers are given on this page.

In Tables 1 and 2, RMS is the root mean square difference between calculated and experimental diagonal 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 chlorine nqcc's.

Subscripts a,b,c refer to the principal axes of the inertia tensor; x,y,z to the principal axes of the nqcc tensor. The nqcc y-axis is chosen coincident with the inertia c-axis, these are perpendicular to the molecular symmetry plane. Ø (degrees) is the angle between its subscripted parameters. ETA = (X_xx - X_yy)/X_zz.


Table 1. ³⁵Cl nqcc's in ClF₂C-CH₂F (MHz). Calculation was made on the ab initio structure with interatomic angles given by (1) MP2/6-311+G(d,p), and (2) B3P86/6-311+G(3d,3p) optimization.

		Calc. (1)		Calc. (2)		Expt. [1]

X_aa	-	58.47	-	57.94	-	57.958(10)
X_bb		21.60		21.13		21.231(11)
X_cc		36.87		36.82		36.727(11)
\|X_ab\|		36.05		36.37

RMS		0.37 (1.0 %)		0.08 (0.2 %)
RSD		0.49 (1.1 %)		0.49 (1.1 %)

X_xx		35.44		35.31		35.40 *
X_yy		36.87		36.82		36.727
X_zz	-	72.31	-	72.13	-	72.13
ETA		0.020		0.021		0.018
Ø_z,a		21.00		21.30		21.28
Ø_a,CCl		21.67		22.12		22.12
Ø_z,CCl		0.67		0.81		0.84

* Calculated here from the experimental diagonal nqcc's and |X_ab| = 36.37 MHz. Calc. (2).


Table 2. ³⁷Cl nqcc's in ClF₂C-CH₂F (MHz). Calculation was made on the ab initio structure with interatomic angles given by (1) MP2/6-311+G(d,p), and (2) B3P86/6-311+G(3d,3p) optimization.

		Calc. (1)		Calc. (2)		Expt. [1]

X_aa	-	46.66	-	46.27	-	46.268(11)
X_bb		17.60		17.25		17.319(13)
X_cc		29.06		29.02		28.949(13)
\|X_ab\|		27.76		28.00

RMS		0.29 (0.9 %)		0.05 (0.2 %)
RSD		0.44 (1.1 %)		0.44 (1.1 %)

Molecular Structure

The molecular structure was optimized at the MP2/6-311+G(d,p) level of theory assuming C_s symmetry. The optimized CC single bond length was then corrected using the equation obtained from linear regression analysis of the data given in Table IX of Ref.[4]. Likewise, the optimized CF bond lengths were corrected by regression analysis of the data given in Table VI of Ref.[3]. For the CCl bond, the structure was optimized at the MP2/6-311+G(2d,p) level and corrected by linear regression analysis of the data given in Table 4 of Ref.[2]. The CH bond lengths were corrected using r = 1.001 r_opt, where r_opt is obtained by MP2/6-31G(d,p) optimization [5]. Interatomic angles used in the calculation are those given by (1) MP2/6-311+G(d,p) and (2) B3P86/6-311+G(3d,3p) optimization.


Table 3. Structure parameters (Å and degrees).

	Cl
	C	1	R1
	C	2	R2	1	A1
	H	3	R3	2	A3	1	D3
	H	3	R3	2	A3	1	- D3
	F	3	R4	2	A4	1	180.
	F	2	R5	3	A5	6	D5
	F	2	R5	3	A5	6	- D5

		MP2 Angles		B3P86 Angles

	R1	1.7624
	R2	1.5085
	R3	1.089
	R4	1.368
	R5	1.338
	A1	109.30		108.96
	A3	109.10		109.10
	A4	108.98		109.23
	A5	110.71		111.20
	D3	60.65		60.50
	D5	59.47		59.86