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		324.40		325.94		317.134(1)
X_bb	-	132.28	-	133.34	-	127.125(2) *
X_cc	-	192.12	-	192.59	-	190.009(2) *
X_ab	-	275.72	-	275.13	-	274.8(6)
X_ac	-	204.12	-	203.90		200.6(9)
X_bc		96.54		95.95		- 96.21(9)

RMS		5.28 (2.50 %)		6.34 (3.03 %)
RSD		1.58 (0.39 %)		1.58 (0.39 %)

X_xx	-	261.78	-	261.92
X_yy	-	263.36	-	263.48
X_zz		525.14		525.40
ETA		0.0030		0.0030
Ø_z,CBr

* Calculated here from experimental X_aa and X_bb - X_cc = 62.884(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		272.21		273.48		266.182(1)
X_bb	-	111.53	-	112.41	-	107.283(2) *
X_cc	-	160.68	-	161.07	-	158.899(2) *
X_ab	-	229.55	-	229.06	-	230.8(7)
X_ac	-	170.51	-	170.32		165.2(1)
X_bc		80.16		79.67		- 78.70(2)

RMS		4.38 (2.47 %)		5.30 (2.99 %)
RSD		1.38 (0.40 %)		1.38 (0.40 %)

* Calculated here from experimental X_aa and X_bb - X_cc = 51.616(3) MHz [1].


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=1.51567226 (1.5138) B2=1.52206976 (1.5199) B3=1.52212706 (1.5200) B4=1.08844907 B5=1.08741258 B6=1.08753957 B7=1.0919256 B8=1.95960837 (1.9631) B9=1.08820925 B10=1.09027101 B11=1.09441872 B12=1.08840715 B13=1.08865222 A1=114.17868821 A2=114.89400493 A3=110.20564634 A4=110.85972927 A5=111.1553349 A6=109.19194066 A7=109.12323787 A8=110.15410304 A9=108.64135185 A10=106.4419763 A11=111.59167483 A12=110.87284247 D1=56.05563844 D2=177.05228836 D3=175.12411962 D4=-64.38612981 D5=55.4403305 D6=123.69350624 D7=-123.41107488 D8=179.72585412 D9=-65.4387373 D10=-63.41052979 D11=57.44270507


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	4616.6	4624.4	4532.801(1)
	B	2008.8	2007.1	1998.3289(1)
	C	1644.4	1643.8	1626.3843(6)

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

2BrButane_G-.html

Last Modified 29 Aug 2016