2-Bromobutane

CH₃CHBrCH₂CH₃

Bromine

Nuclear Quadrupole Coupling Constants

in 2-Bromobutane, G+

Calculation of the bromine nqcc tensors was made here on molecular structures given by MP/6-311+G(3df,3pd) optimization, and on these same structure but with empirically corrected approximate equilibrium C-C and CBr bond lengths. These calculated nqcc's are compared with the experimental values in Tables 1 and 2. Structure parameters are given in Table 3, rotational constants 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. ETA = (X_xx - X_yy)/X_zz. Ø_z,CBr (degrees) is the angle between the z-principal axis and the CCl bond direction.

RMS is the root mean square difference between calculated and experimental diagonal nqcc's (percentage of the average of the magnitudes of the experimental nqcc's). RSD is the calibration residual standard deviation of the B1LYP/TZV(3df,3p) model for calculation of the efg's/nqcc's.


Table 1. ⁷⁹Br nqcc's in 2-Bromobutane, G+ (MHz).

Calc (1) was made on the MP2/6-311+G(3df,3pd) optimized molecular structure.
Calc (2) was made on this same structure but with empirically corrected C-C and CBr bond lengths.

		Calc (1)		Calc (2)		Expt. [1]

X_aa		304.09		306.93		300.1367(2)
X_bb		- 83.07		- 85.69		- 82.2620 *
X_cc	-	221.01	-	221.24	-	217.8747 *
X_ab	-	324.64	-	323.35		321.18(6)
X_ac	-	141.75	-	141.93	-	140.93(2)
X_bc		82.43		81.80		- 82.16(1)

RMS		2.95 (1.47 %)		4.81 (2.40 %)
RSD		1.58 (0.39 %)		1.58 (0.39 %)

X_xx	-	256.82	-	256.95
X_yy	-	267.72	-	267.90
X_zz		524.54		524.86
ETA		0.0208		0.0209
Ø_z,CBr

* Calculated here from experimental X_aa and X_bb - X_cc = 135.6128(3) MHz [1].


Table 2. ⁸¹Br nqcc's in 2-Bromobutane, G+ (MHz).

Calc (1) was made on the MP2/6-311+G(3df,3pd) optimized molecular structure.
Calc (2) was made on this same structure but with empirically corrected CBr bond length.

		Calc (1)		Calc (2)		Expt. [1]

X_aa		257.21		258.54		253.8573(2)
X_bb		- 72.50		- 74.63		- 71.7862 *
X_cc	-	184.72	-	184.91	-	182.0711 *
X_ab	-	269.38	-	268.30		266.64(9)
X_ac	-	118.69	-	118.83	-	117.00(2)
X_bc		68.12		67.59		- 68.25(2)

RMS		2.50 (1.48 %)		4.02 (2.37 %)
RSD		1.38 (0.40 %)		1.38 (0.40 %)


Table 3. 2-Bromobutane, G+. MP2/6-311+G(3df,3pd) structure parameters (Å and degrees). Approximate equilibrium bond lengths are given in parentheses.


	C C,1,B1 C,2,B2,1,A1 C,3,B3,2,A2,1,D1,0 H,4,B4,3,A3,2,D2,0 H,1,B5,2,A4,3,D3,0 H,1,B6,2,A5,3,D4,0 H,1,B7,2,A6,3,D5,0 Br,2,B8,1,A7,3,D6,0 H,2,B9,1,A8,3,D7,0 H,3,B10,2,A9,1,D8,0 H,3,B11,2,A10,1,D9,0 H,4,B12,3,A11,2,D10,0 H,4,B13,3,A12,2,D11,0

	B1=1.51516215 (1.5134) B2=1.51797573 (1.5160) B3=1.52080165 (1.5187) B4=1.08853289 B5=1.08741528 B6=1.08906805 B7=1.09128492 B8=1.95803152 (1.9616) B9=1.08972552 B10=1.09431178 B11=1.09190771 B12=1.08784128 B13=1.09013706 A1=112.66252365 A2=114.2656821 A3=110.7318347 A4=111.38001003 A5=110.34717195 A6=109.23160422 A7=108.71726415 A8=110.75981546 A9=106.41671085 A10=108.68717518 A11=110.98932168 A12=110.7145707 D1=-174.57073294 D2=176.37092333 D3=-179.57403814 D4=-58.95451886 D5=60.33852906 D6=122.33465888 D7=-123.94556929 D8=-53.56852365 D9=61.34716513 D10=-63.39638744 D11=56.64522967


Table 4. 2-Bromobutane, G+. Rotational constants (MHz), ⁷⁹Br species.

	r (1) = MP2/6-311+G(3df,3pd) opt structure.
	r (2) = r (1) but with corrected C-C and CBr bond lengths.

		r (1)	r (2)	Expt. [1]

	A	3894.7	3899.6	3857.83420(2)
	B	2296.7	2294.1	2272.32632(2)
	C	1537.3	1536.8	1520.60969(1)

[1] S.Ka, J.Kim, H.Jang, J.J.Oh, Abstract MG03, 70th International Symposium on Molecular Spectroscopy, Champaign-Urbana, 2015.

2BrButane.html

Last Modified 19 July 2015