CH3CH2(S,Se)CN

CH₃CH₂-X-CN: X=S,Se

Nitrogen

Nuclear Quadrupole Coupling Constants

in Ethyl Thio- and Seleno-cyanate

The microwave spectrum of ethyl thiocyanate was observed and assigned by Bjørseth and Marstokk [1], and ethyl selenocyanate by Sakaizuma and Itakura [2]. Rotational constants and dipole moments were determined.

For each title molecule, shown below, calculation of the nitrogen nqcc tensor was made on a molecular structures given by MP2/6-311+G(3df,3pd) optimization with empirically corrected approximate equilibrium single CC and triple CN bond lengths. These calculated nqcc's are given in Tables 1 and 2. Structure parameters are given in Z-Matrix format in Table 3, rotational constants and dipole moments in Table 4.

Ethyl thiocyanate

Ethyl selenocyanate

Dihedral CCSC = 61.9^o

Dihedral CCSeC = 60.6^o

In Tables 1 and 2, subscripts a,b,c refer to the principal axes of the inertia tensor; x,y,z to the principal axes of the nqcc tensor. ETA = (X_xx - X_yy)/X_zz. Ø (degrees) is the angle between its subscripted parameters.

RSD is the calibration residual standard deviation of the B3PW91/6-311+G(df,pd) model for calculation of the nitrogen efg's/nqcc's.


Table 1. Nitrogen nqcc tensor in Ethyl thiocyanate (MHz). Calculation was made on molecular structure given by MP2/6-311+G(3df,3pd) optimization, with approximate r_e single CC and triple CN bond lengths.

			Calc	Expt

¹⁴N	X_aa	-	0.661
	X_bb	-	0.603
	X_cc		1.264
	X_ab	-	3.322
	X_ac	-	0.830
	X_bc		0.176

	RSD		0.030 (1.3 %)

	X_xx		1.008
	X_yy		2.987
	X_zz	-	3.996
	ETA		0.495
	Ø_z,CN		0.40


Table 2. Nitrogen nqcc tensor in Ethyl selenocyanate (MHz). Calculation was made on molecular structure given by MP2/6-311+G(3df,3pd) optimization, with approximate r_e single CC and triple CN bond lengths.

			Calc	Expt

¹⁴N	X_aa	-	0.459
	X_bb	-	0.924
	X_cc		1.383
	X_ab	-	3.414
	X_ac	-	0.566
	X_bc		0.147

	RSD		0.030 (1.3 %)

	X_xx		1.223
	X_yy		2.905
	X_zz	-	4.128
	ETA		0.408
	Ø_z,CN		0.31


Table 3. CH₃CH₂-X-CN, X=S,Se: MP2/6-311+G(3df,3pd) optimized structure parameters (Å and degrees). Approximate r_e bond lenths are given in parentheses.

Ethyl thiocyanate				Ethyl selenocyanate
		C C,1,B1 H,1,B2,2,A1 H,1,B3,2,A2,3,D1,0 H,1,B4,2,A3,4,D2,0 H,2,B5,1,A4,5,D3,0 H,2,B6,1,A5,5,D4,0 X,2,B7,1,A6,5,D5,0 C,8,B8,2,A7,1,D6,0 N,9,B9,2,A8,1,D7,0


	B1=1.51599151 (1.5141) B2=1.08763703 B3=1.08936661 B4=1.08841553 B5=1.08767378 B6=1.08993972 B7=1.82024887 B8=1.68386981 B9=1.17643598 (1.1609) A1=110.87852519 A2=109.65244951 A3=110.69143711 A4=112.13954362 A5=111.66827931 A6=113.23780586 A7=98.09485669 A8=137.76991586 D1=120.10162914 D2=119.32171762 D3=60.38617404 D4=-177.89600381 D5=-62.07899607 D6=61.92291678 D7=53.80291966		B1=1.51563583 (1.5138) B2=1.0877583 B3=1.08996879 B4=1.08848716 B5=1.08701077 B6=1.0899813 B7=1.96003924 B8=1.83238579 B9=1.17617212 (1.1607) A1=111.05161745 A2=109.61248305 A3=110.82449669 A4=112.42612556 A5=112.04826818 A6=113.11508786 A7=94.96373213 A8=135.58561198 D1=120.04935107 D2=119.28079231 D3=59.85828092 D4=-177.62396892 D5=-61.65721097 D6=60.55745631 D7=52.64307017


Table 4. CH₃CH₂-X-CN, X=S,Se: Rotational Constants (MHz) and Dipole Moments (D).

		____CH₃CH₂-S-CN____		____CH₃CH₂-Se-CN____
		Calc	Expt [1]	Calc	Expt [2]

	A	6259	6283.90(2)	3881	3922.92(18)
	B	3154	3083.540(9)	2978	2898.00(8)
	C	2281	2245.224(9)	1811	1789.82(2)
	\|µ_a\|	4.17	3.80(10)	4.21	4.37(10)
	\|µ_b\|	1.08	1.13(5)	1.41	0.80(5)
	\|µ_c\|	0.33	0.61(4)	0.30	0.50(5)

[1] A.Bjørseth and K.M.Marstokk, J.Mol.Struct. 11,15(1972).

[2] T.Sakaizuma and T.Itakura, J.Mol.Spectrosc. 163,1(1994).

Ethylcyanate

HSCN

ClSCN

BrSCN

Propargylthiocyanate

Propargylselenocyanate

Table of Contents

Molecules/Nitrogen

CH3CH2XCN.html

Last Modified 17 Feb 2014