2-Bromobutane

CH₃CHBrCH₂CH₃

Bromine

Nuclear Quadrupole Coupling Constants

in 2-Bromobutane, A

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, A (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		452.42		452.96		446.043(9)
X_bb	-	223.65	-	224.04	-	219.206(5) *
X_cc	-	228.77	-	228.92	-	226.837(5) *
X_ab	-	176.07	-	175.69		179.19(4)
X_ac	-	147.67	-	147.68		145.47(9)
X_bc		35.52		35.38		36.62(3)

RMS		4.62 (1.55 %)		5.02 (1.69 %)
RSD		1.58 (0.39 %)		1.58 (0.39 %)

X_xx	-	259.28	-	259.40
X_yy	-	266.80	-	266.97
X_zz		526.08		526.37
ETA		0.0143		0.0144
Ø_z,CBr

* Calculated here from experimental X_aa and X_bb - X_cc = 7.632(3) MHz [1].


Table 2. ⁸¹Br nqcc's in 2-Bromobutane, A (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		378.39		378.85		372.949(9)
X_bb	-	187.25	-	187.58	-	183.533(5) *
X_cc	-	191.14	-	191.27	-	189.416(5) *
X_ab	-	146.34	-	146.02		179.19(4)
X_ac	-	123.38	-	123.39		145.47(9)
X_bc		29.50		29.38		36.62(3)

RMS		3.93 (1.58 %)		4.26 (1.72 %)
RSD		1.38 (0.40 %)		1.38 (0.40 %)

* Calculated here from experimental X_aa and X_bb - X_cc = 5.884(3) MHz [1].


Table 3. 2-Bromobutane, A. 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=1.51545752 (1.5136) B2=1.51973201 (1.5177) B3=1.52617679 (1.5238) B4=1.08856528 B5=1.08730449 B6=1.08961924 B7=1.09004283 B8=1.95694414 (1.9605) B9=1.08956369 B10=1.09173514 B11=1.08995876 B12=1.09038719 B13=1.0880729 A1=113.97576719 A2=112.0941304 A3=110.31547529 A4=111.01653353 A5=110.28381404 A6=109.89695425 A7=108.8362257 A8=110.60240098 A9=108.69278158 A10=108.74531061 A11=110.96780131 A12=111.81623254 D1=-63.3036092 D2=-173.95460532 D3=-176.52486714 D4=-56.14954599 D5=63.69537036 D6=121.55066206 D7=-124.6389645 D8=59.0281426 D9=175.22650688 D10=-54.55922985 D11=66.26343267


Table 4. 2-Bromobutane, A. 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	6552.1	6563.2	6412.915(3)
	B	1565.8	1564.7	1555.2157(4)
	C	1329.2	1328.8	1316.55295(3)

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

2BrButane_A.html

Last Modified 29 Aug 2016