Methyl Chloroform

H₃C-CCl₃

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Chlorine

Nuclear Quadrupole Coupling Constants

in Methyl Chloroform

The complete chlorine nqcc tensor in methyl chloroform was determined by Dore and Kisiel [1]. Carpenter et al. [2] had previously determined the component along the CCl bond. An effective molecular structure was reported by Holm et al. [3]. An ab initio equilibrium structure was derived by Margulès et al. [4].

Calculation of the chlorine nqcc's in methyl chloroform was made on a molecular structure derived ab initio, with bond length corrections (see below). These are compared with the experimental values in Tables 1 and 2. Structure parameters and atomic coordinates are given in Tables 3 and 4, respectively.

The results of calculation made on the effective molecular structure of Holm et al. can be seen here.

The results of calculation made on the ab initio equilibrium structure of Margulès et al. can be seen here.

Coordinate Systems

X_uu is the component of the nqcc tensor along the threefold symmetry axis. Corresponding to the atomic coordinates given below in Table 4, X_vv and X_ww are the components along the v- and w- axes for the Cl atom in the uv-plane.

Subscripts x,y,z refer to the principal axes of the nqcc tensor. The y-axis is chosen coincident with the w-axis. Ø (degrees) is the angle between its subscripted parameters. ETA = (X_xx - X_yy)/X_zz.

RMS is the root mean square difference between caalculated and experimental diagonal nqcc's (percent of the average experimental nqcc). RSD is the residual standard deviation of calibration of the model for calculation of the nqcc's.


Table 1. Chlorine nqcc's in H₃C-CCl₃ (MHz). The subscripts cc, etc. in parentheses are the axes labels of Ref. [1].

			Calc.		Expt. [1]

³⁵Cl	X_uu(cc)		26.92		26.8907(9)
	X_vv(aa)	-	65.74	-	65.5378(12)
	X_ww(bb)		38.82		38.6472(12)
	X_uv(ac)		36.66		36.510(23)

	RMS		0.15 (0.35 %)
	RSD		0.49 (1.1 %)

	X_xx		39.68		39.571(14)
	X_yy		38.82		38.6472(12)
	X_zz	-	78.49	-	78.218(14)
	ETA	-	0.0109	-	0.0118(2)
	Ø_z,u		70.82		70.846(9)
	Ø_u,CCl		69.80		69.82 *
	Ø_z,CCl		1.03		1.05 *

* Calculated here.

The pyramid formed by the z-principal axes of the three Cl nqcc tensors is somewhat 'flatter' than the molecular pyramid. This is typical of the pyramidal trichlorides.


Table 2. ³⁷Cl nqcc's in ³⁷Cl³⁵Cl₂CCH₃ (MHz).

			Calc.		Expt. [1]

³⁷Cl	X_aa	-	52.46	-	52.3028(16)
	X_bb		30.59		30.4585(16)
	X_cc		21.87		21.8443(11)
	\|X_ac\|		28.05		28.032(76)

	RMS		0.12 (0.35 %)
	RSD		0.44 (1.1 %)

	X_xx		31.27		31.249(46)
	X_yy		30.59		30.4585(16)
	X_zz	-	61.86	-	61.708(46)
	ETA	-	0.0109	-	0.0128(7)
	Ø_z,c		71.48		71.45(4)
	Ø_c,CCl		70.45		70.45 *
	Ø_z,CCl		1.03		1.00 *

* Calculated here.

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. [7]. Likewise, the optimized CF bond lengths were corrected by regression analysis of the data given in Table VI of Ref. [6]. 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. [5]. The CH bond lengths were corrected using r = 1.001 r_opt, where r_opt is obtained by MP2/6-31G(d,p) optimization [8]. Interatomic angles used in the calculation are those given by B3P86/6-311+G(3d,3p) optimization.


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

	CCl	1.7724
	CC	1.507
	CH	1.087
	CCH	109.33
	CCCl	110.20


Table 3. Atomic coordinates.
(More figures are shown than are significant.)

			u (Å)		v (Å)		w (Å)

	Cl	-	0.360966		1.663358		0.0
	Cl	-	0.360966	-	0.831679	±	1.440510
	C		0.251115		0.0		0.0
	C		1.758115		0.0		0.0
	H		2.117952	-	1.025713		0.0
	H		2.117952		0.512856	±	0.888293