1,2,5-Oxadiazole

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Nitrogen

Nuclear Quadrupole Coupling Constants

in 1,2,5-Oxadiazole (Furazan)

Nitrogen nqcc's in furazan and its molecular structure were reported in 1965 by Saegebarth and Cox [1]. Stiefvater in 1988 measured the nqcc's in mono-deuterated furazan [2], and determined the complete substitution structure [3].

Calculation was made here of the nitrogen nqcc's on the structure of Stiefvater. These results are compared with the experimental values [2] in Tables 1 and 2. Structure parameters are shown in Table 3.

Several experimental structures and an ab initio equilibrium structure were determined by Vázquez, et al. [4]. Results of calculation of the nqcc's on these several structures are summarized in Table 4.

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. The nqcc y-axis is chosen coincident with the inertia c-axis, these are perpendicular to the molecular plane. 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 nqcc's (percentage of the average of the magnitudes of the experimental nqcc's). RSD is the calibration residual standard deviation of the B3PW91/6-311+G(df,pd) model for calculation of nitrogen nqcc's.


Table 1. N(2) nqcc's in 3-d₁-Furazan (MHz). Calculation was made on the r_s structure of Stiefvater [3].

			Calc.		Expt. [2]

¹⁴N(2)	X_aa		3.536		3.546(10)
	X_bb	-	4.686	-	4.690(10)
	X_cc		1.150		1.144(10)
	\|X_ab\|		2.790		2.764

	RMS		0.007 (0.2 %)
	RSD		0.030 (1.3 %)

	X_xx		4.394		4.39(4)
	X_yy		1.150		1.14(4)
	X_zz	-	5.544	-	5.53(4)
	ETA	-	0.585	-	0.5863
	Ø_z,a		72.9		73.07
	Ø_a,bi		48.5		48.47
	Ø_z,bi*		24.4		24.6

* The z-axis makes an angle of 24.4^o with the external bisector ('bi') of the ONC angle and tilts toward O(1).


Table 2. N(5) nqcc's in 3-d₁-Furazan (MHz). Calculation was made on the r_s structure of Stiefvater [3].

			Calc.		Expt. [2]

¹⁴N(5)	X_aa	-	5.070	-	5.044(10)
	X_bb		3.920		3.900(10)
	X_cc		1.150		1.144(10)
	\|X_ab\|		2.116		2.144

	RMS		0.020 (0.6 %)
	RSD		0.030 (1.3 %)


Table 3. Molecular structure parameters, r_s[3] (Å and degrees).

	ON	1.3729
	NC	1.3032
	CC	1.4211
	CH	1.0763
	NON	111.15
	ONC	105.53
	NCC	108.89
	CCH	130.16


Table 4. ¹⁴N nqcc's in 3-d₁-Furazan (MHz). RMS is the root mean square difference between calculated and experimental diagonal nqcc's. Calculation was made on each of the structures listed in column one [4]. a,b,c, etc. (column two) are references to footnotes in Table 10 of Ref. [4] which explain, for example, the difference in derivation of the two r_s (d and g) structures.

			X_aa	X_bb	X_cc	\|X_ab\|	RMS

r_e	a	N(2)	3.560	-4.761	1.161	2.679	0.053
		N(5)	-5.145	3.984	1.161	1.954	0.076

r_z		N(2)	3.535	-4.649	1.114	2.785	0.030
		N(5)	-5.025	3.910	1.114	2.131	0.021

r_e(z)	b	N(2)	3.624	-4.771	1.147	2.650	0.065
		N(5)	-5.149	4.002	1.147	1.924	0.085

r_o	c	N(2)	3.537	-4.666	1.129	2.783	0.017
		N(5)	-5.044	3.915	1.129	2.121	0.012

r_s	d	N(2)	3.535	-4.679	1.144	2.792	0.009
		N(5)	-5.063	3.919	1.144	2.121	0.015

r_m¹	e	N(2)	3.530	-4.688	1.158	2.798	0.012
		N(5)	-5.075	3.918	1.158	2.120	0.022

r_m¹	f	N(2)	3.519	-4.682	1.164	2.811	0.020
		N(5)	-5.072	3.908	1.164	2.135	0.020

r_s	g	N(2)	3.540	-4.683	1.144	2.786	0.005
		N(5)	-5.066	3.922	1.144	2.113	0.018

r_m¹	h	N(2)	3.529	-4.687	1.158	2.800	0.013
		N(5)	-5.075	3.917	1.158	2.122	0.022

r_m²	i	N(2)	3.525	-4.687	1.162	2.803	0.016
		N(5)	-5.075	3.913	1.162	2.126	0.022

r_m^rho	j	N(2)	3.545	-4.664	1.118	2.770	0.021
		N(5)	-5.039	3.921	1.118	2.111	0.019

r_m^rho	k	N(2)	3.375	-4.555	1.180	2.992	0.128
		N(5)	-4.986	3.806	1.180	2.312	0.064

[1] E.Saegebarth and A.P.Cox, J.Chem.Phys. 43,166(1965).

[2] O.L.Stiefvater, Z.Naturforsch. 43a,607(1988).

[3] O.L.Stiefvater, Z.Naturforsch. 43a,597(1988).

[4] J.Vázquez, J.Demaison, J.J.López-González, J.E.Boggs, and H.D.Rudolph, J.Mol.Spectrosc. 207,224(2001).

Oxazole

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Last Modified 24 May 2003