Methyl Cyanide

CH₃CN

Deuterium and Nitrogen

Nuclear Quadrupole Coupling Constants

in Methyl Cyanide

Deuterium nqcc's in fully deuterated methyl cyanide were determined by Murray and Kukolich [1]. A number of measurements of the nitrogen nqcc in the normal species have been reported [1 - 6]. Deuterim and nitrogen nqcc's have been determined in the d₁ species by Merke et al. [7]. LeGuennec et al. [8] determined an equilibrium structure.

Calculation of the deuterium and nitrogen nqcc's was made here on the equilibrium structure. These nqcc's are compared with the experimental values in Tables 1 -3. Structure parameters and atomic coordinates respectively are given in Tables 4 and 5.

Coordinate Systems

Subscripts u,v,w refer to the coordinate axes defined in Table 4. The u-axis is along the threefold symmetry axis. The nqcc's given below with these subscripts are those for the D atom in the uv-plane.

Subscripts a,b,c refer to the principal inertial axis.

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 calculated and experimental diagonal nqcc's. RSD is the residual standard deviation of calibration of the models for calculation of the nqcc's.


Table 1. Deuterium nqcc's in CD₃CN (kHz).

		Calc.	Expt. [1]

²H	X_uu	- 56.2	- 55.1(4)
	X_vv	153.6
	X_ww	- 97.4
	X_uv	- 90.6

	RSD	1.1 (0.86 %)

	X_xx	- 89.8
	X_yy	- 97.4
	X_zz	187.2
	ETA	0.040
	Ø_z,u	69.60
	Ø_u,CD	69.90
	Ø_z,CD	0.30


Table 2. Nitrogen nqcc's in CH₃CN (MHz).

			Calc.		Expt.

¹⁴N	X_zz	-	4.208	-	4.22410(98) [2]
				-	4.2292(6) [1]
				-	4.22534(73) [3]
				-	4.22473(80) [4]
				-	4.54667 [5]
				-	4.214(16) [6]

The difference between calculated and experimental [1-3] ¹⁴N nqcc's is 16-21 kHz (0.4 - 0.5 %).


Table 3. Deuterium (kHz) and Nitrogen (MHz) nqcc's in CH₂DCN.

			Calc.		Expt. [7]

²H	X_aa		- 50.3		- 56.2(54)
	X_bb		147.7		151.6(51)
	X_cc		- 97.4		- 95.4(52)
	\|X_ab\|		96.9

	RMS		4.2 (4.2 %)
	RSD		1.1 (0.86 %)

¹⁴N	X_aa	-	4.202	-	4.2183(23)
	X_bb		2.098		2.1100(30)
	X_cc		2.104		2.1083(29)
	\|X_ab\|		0.197

	RMS		0.012 (0.42 %)
	RSD		0.030 (1.3 %)


Table 4. Structure parameters, r_e[8] (Å and degrees).

	CH	1.087
	CC	1.457
	CN	1.156
	HCC	110.1


Table 5. Atomic coordinates, r_e
(More figures are shown than are significant.)

			u (Å)		v (Å)		w (Å)

	H	-	1.550012		1.020795		0.0
	H	-	1.550012	-	0.510398	±	0.884035
	C	-	1.176454		0.0		0.0
	C		0.280546		0.0		0.0
	N		1.436546		0.0		0.0

[1] A.M.Murray and S.G.Kukolich, J.Chem. Phys. 78,3557(1983).

[2] M.Simeckova, S.Urban, U.Fuchs, F.Lewen, G.Winnewisser, I.Morino, and K.M.T.Yamada, J.Mol.Spectrosc. 226,123(2004).

[3] D.Boucher, J.Burie, J.Demaison, A.Dubrille, J.Legrand, and B.Segard, J.Mol.Spectrosc. 64,290(1977).

[4] G.Cazzoli and C.Puzzarini, J.Mol.Spectrosc. 240,153(2006). Corrigendum: 247,187(2008).

[5] I.An, W.M.Rhee, and J.A.Roberts, J.Chem.Phys. 86,4725 (1987).

[6] M.K.Kemp, J.M.Pochan, and W.H.Flygare, J.Phys.Chem. 71,765 (1967).

[7] I.Merke, W.Stahl, and H.Dreizler, Z.Naturforsch. 49a,490(1994).

[8] M.LeGuennec, G.Wlodarczak, J.Burie, and J.Demaison, J.Mol. Spectrosc. 154,305(1992).

J.Demaison, A.Dubrille, D.Boucher, J.Burie, and V.Typke, J.Mol.Spectrosc. 76,1(1979): r_z structure.

C.Puzzarini and G.Cazzoli, J.Mol.Spectrosc. 240,260(2006): Semi-experimental r_e structures; and (all)CCSD(T)/cc-pwCVQZ calculation of eQq, which gives -4.22 MHz.