CH3SSCH3
	Sulfur
	Nuclear Quadrupole Coupling Constants
		in Dimethyl Disulfide
	The complete nqcc tensor for 33S in CH333S32SCH3 was determined by Hartwig et al. [1].  A molecular ro structure was derived by Sutter et al. [2].  Calculation of the nqcc tensor was made here on this structure, and on this structure but with the geometry of the methyl groups determined ab initio as described below.
	Calculated and experimental nqcc tensors are compared in Tables 1 and 2.  Structure parameters are given in Table 3, atomic coordinates in Table 4.
	In Tables 1 and 2, subscripts a,b,c refer to the principal axes of the inertia tensor, subscripts x,y,z to the principal axes of the nqcc tensor.  Ø (degrees) is the angle between its subscripted parameters. ETA = (Xxx - Xyy)/Xzz.
	RMS is the root mean square difference between calculated and experimental nqcc's (percentage of average experimental nqcc).  RSD are the residual standard deviations of calibration of the B3LYP/6-311G(3df,3p) and B3LYP/TZV+(3df,3p) models for calculation of the nqcc's.
	Table 1.  33S nqcc's in CH333S32SCH3 (MHz).  Calculation was made with the B3LYP/6-311G(3df,3p) model on the ro and ro/ropt structures.     Calc. ro Calc. ro/ropt Expt. [1]     Xaa - 30.41 - 29.94 - 29.6475(42) Xbb 13.26 12.86 12.807(31) Xcc 17.15 17.08 16.840(26) Xab* - 21.52 - 21.90 20.2(13) Xac* 15.63 15.61 18.3(12) Xbc* - 24.59 - 24.73 24.43(17)   RMS 0.54 (2.8 %) 0.22 (1.1 %) RSD 0.39 (1.7 %) 0.39 (1.7 %)   Xxx - 8.70 - 8.97 - 9.52(32) Xyy - 39.84 - 39.69 - 39.2(11) Xzz 48.54 48.66 48.7(12) ETA 0.641 0.631 Øz,n**   0.5   0.3 Øx,bi** 12.1 11.4
	Here and in Table 2 below,
	* the algebraic signs of the off-diagonal nqcc's correspond to the atomic coordinate given in Table 4.  The experimental off-diagonal components are absolute values.
	** the z-principal axis makes an angle of Øz,n with the normal (n) to the C(2)33S(1)S(2) plane, the x-axis makes an angle of Øx,bi with the bisector (bi) of the C(2)33S(1)S(2) angle.
	Table 2.  33S nqcc's in CH333S32SCH3 (MHz).  Calculation was made with the B3LYP/TZV+(3df,3p) model on the ro and ro/ropt structures.     Calc. ro Calc. ro/ropt Expt. [1]     Xaa - 30.46 - 29.98 - 29.6475(42) Xbb 13.36 12.96 12.807(31) Xcc 17.10 17.03 16.840(26) Xab* - 21.50 - 21.88 20.2(13) Xac* 15.78 15.76 18.3(12) Xbc* - 24.60 - 24.74 24.43(17)   RMS 0.58 (3.0 %) 0.24 (1.2 %) RSD 0.35 (1.5 %) 0.35 (1.5 %)   Xxx - 8.74 - 9.01 - 9.52(32) Xyy - 39.89 - 39.74 - 39.2(11) Xzz 48.62 48.74 48.7(12) ETA 0.641 0.630 Øz,n**   0.4   0.3 Øx,bi** 12.4 11.7
	For the ro structure, all CH bond lengths and SCH angles are assumed equal.  For the ro/ropt structure, methyl geometries are given by MP2/6-31G(d,p) optimization, with CH bond lengths corrected using r(CH) = 1.001*ropt(CH) [3].
	Table 3. Molecular structure parameters, ro and ro/ropt (Å and degrees).  Complete structures are given here in Z-matrix format.     ro ro/ropt SS 2.038 2.038 SC 1.810 1.810 SSC 102.8 102.8 CSSC   84.7   84.7 CH(4,8) 1.097 1.090 CH(5,9) 1.097 1.088 CH(6,10) 1.097 1.087 SCH(4,8) 108.9 106.6 SCH(5,9) 108.9 111.5 SCH(6.10) 108.9 110.8
	Table 4.  CH333S32SCH3 Atomic coordinates, ro/ropt.   a (Å) b (Å) c (Å) 33S 0.9099 - 0.4308 - 0.4326 32S - 0.9264 - 0.4272 0.4514    C 1.7826 0.8863 0.4503    H 2.7961 0.9120 0.0497    H 1.3157 1.8547 0.2833    H 1.8239 0.6754 1.5158    C - 1.8078 0.8643 - 0.4602    H - 2.8214 0.8921 - 0.0603    H - 1.3473 1.8392 - 0.3146    H - 1.8475 0.6298 - 1.5209
	1,2-Dithiin		Disulfane
	[1] H.Hartwig, U.Kretschmer, and H.Dreizler, Z.Naturforsch. 50a,131(1995).
	[2] D.Sutter, H.Dreizler, and H.D.Rudolph, Z.Naturforsch. 20a,1676(1965).
	[3] J.Demaison and G.Wlodarczak, Struct.Chem. 5,57(1994).
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						Last Modified 18 April 2006