Rotational Spectra Of Cyclopropylmethyl
Germane And Cyclopropylmethyl Silane:
Dipole Moment And Barrier To Methyl
Group Rotation
Rebecca A. Peebles, Sean A. Peebles, Michael D. Foellmer,
Jonathan M. Murray, Michal M. Serafin, Amanda L. Steber
Department Of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL 61920
Gamil A. Guirgis, Richard Liberatore
Department Of Chemistry And Biochemistry, The College Of Charleston, Charleston, SC 29424
James R. Durig, Charles J. Wurrey
Department Of Chemistry, University Of Missouri - Kansas City, Kansas City, MO 64110
Introduction
• Three possible conformers
• Possible methyl group internal
rotation
• Multiple isotopologues
• 70Ge, 72Ge, 73Ge, 74Ge, 76Ge
Ge or Si
• 28Si, 29Si, 30Si
• Only one isotope (73Ge, I =
9/2) is quadrupolar
• Model for fitting internal rotation
Conformers
cis
gauche
H
H
H
H
CH2
CH2
Me
H
trans
H Me
Me
CH2
CH2
H
H
CH2
CH
H 2
Cyclopropylmethylgermane (CMG)
gauche
cis
trans
Relative
Energy / cm-1
55
0
521
A / MHz
B / MHz
C / MHz
ma / D
5620
2110
1805
0.52
7184
1889
1653
0.21
8089
1718
1645
0.12
mb / D
mc / D
mtot / D
0.41
0.62
0.73
0.00
0.66
0.30
0.72
0.00
0.74
MP2/6-311+G(d), no ZPE corrections
CMG Experimental Technique
• Samples synthesized at College of Charleston (SC)
• Fourier-transform microwave (FTMW)
spectroscopy at Eastern Illinois University
• Liquid samples
• Vapor pressure = ~3 Torr
• Transferred as vapor to glass bulb
• Concentration <0.5% in ~1 atm He/Ne
• Optimizations at MP2/6-311+G(d) level
• No ZPE corrections
25
a.
74Ge
76Ge
20
72Ge
36.5%
7.8%
70Ge
27.4%
73Ge
20.5%
7.8%
15
10
5
0
8840
8840
8860
8860
8880
8880
8900
8900
8920
8920
8940
8940
8960
8960
Frequency / MHz
b.
E
76Ge 1
11
•Combination of
two data files
•100 scans each
•S/N ~ 40
- 000
A
8857.0000
8857
8858.0000
8858
8859.0000
8859
8860.0000
8860
8861.0000
8861
CMG Fit Using XIAM1
Parameter
70Ge
72Ge
73Ge
74Ge
76Ge
7208.0673(8)
7183.7621(11)
A / MHz
7260.0925(10)
7233.4857(10) 7220.6101(26)
B / MHz
1938.36354(35)
1932.3070(4)
1929.3477(11) 1926.45300(26)
1920.7902(4)
C / MHz
1692.92029(33)
1686.9185(4)
1683.9929(11) 1681.13359(25)
1675.5568(4)
DJ / kHz
0.618(8)
0.622(8)
0.48(4)
0.600(6)
0.597(9)
DJK / kHz
–4.4(9)
–4.358(26)
–4.7(7)
–4.29(7)
–4.18(10)
dJ / kHz
0.183(5)
0.179(6)
0.179(fixed)
0.195(4)
0.181(6)
V3 / kJ mol–1
4.753(8)
4.737(8)
4.734(23)
4.736(6)
4.740(9)
F0 / GHz
159.8(3)
159.1(3)
159.2(7)
159.18(21)
159.3(3)
Ia / u Å 2
3.163(5)
3.176(6)
3.175(13)
3.175(4)
3.173(6)
d / rad
0.8529(4)
0.8537(10)
0.858(4)
0.8580(7)
0.8593(10)
2.63
3.44
5.07
2.10
3.00
36
52
54
36
36
s.d. / kHz
N
1XIAM:
H.Hartwig and H.Dreizler, Z.Naturforsch, 51a (1996) 923.
CMG Comparison With Ab Initio
Ab Initio
Observed
A / MHz
7184
7208.0672(7)
B / MHz
1889
1926.4530(3)
a
b
c
C / MHz
1653
1681.1335(2)
Ia / u Å2
~3.1a
3.179(4)
V3 / kJ mol-1
4.2
4.729(6)
qia / 
48.5
49.19(4)
ma / D
0.21
0.1782(10)
qib / 
41.8
40.90(4)
mb / D
0.62
0.581(4)
qic / 
85.8
87.7 b
mc / D
0.31
0.305(9)
mtot / D
0.72
0.680(5)
a
Estimate, used as XIAM input
b Angle e fixed at 3°
c For 72Ge
Ab Initio c Observed c
73Ge
Quadrupole Coupling Constants
• Series of density functional theory predictions with varying
basis sets – B3LYP worked best
Basis Set
1 For
ClGeH3 czz / MHz MeGeH3 czz / MHz
aug-cc-pvdz
–74.2
1.0
6-311++G(2d,2p)
–94.5
2.0
aug-cc-pvtz
–88.3
2.1
6-311++G(3df,3pd)
–93.3
1.5
aug-cc-pvqz
–87.8
1.5
aug-cc-pv5z
–90.6
2.3
Experiment1
–93.032(15)
3 (max)
many calculated quadrupole coupling constants and comparison with experimental data: http://turbo.kean.edu/~wbailey/TOC.html
73Ge
E
110 - 000
11  9
2
2
E
9 9
2
2
A
A
E
9148
9148
9148.5
9148.5
9149
9149
9149.5
9150
9150.5
9150
9149.5
9150.5
Frequency
Frequency/ /MHz
MHz
9151
9151
A 7 9
2
2
9151.5
9151.5
9152
9152
9 7
2
2
13  11
2
2
73Ge
212 - 101
9  11
2
2
11  11
2
2
5 7
2
2
A state
E state
11  9
2
2
9 9
2
2
7 9
2
2
7 7
2
2
12270 12270.5
12271 12271.5
12272 12272.5
12273 12273.5 12274 12274.5
12275
12270 12270.5
12271
12272 12272.5
12273 12273.5
12275
Predicted
B3LYP/6-311++G(3df,3pd)
Observed
12271.5
Frequency / MHz
12274 12274.5
Comparison with Calculated 73Ge Coupling
Constants
Parameter
Experimental
Predicted
% Difference
caa / MHz
8.134(8)
7.914
–2.7
cbb – ccc / MHz
7.693(26)
7.716
0.3
caa / MHz
8.134(8)
7.914
–2.7
cbb / MHz
–0.2205
–0.099
–55
ccc / MHz
–7.9135
–7.815
–1.2
Comparison of Experimental 73Ge
Coupling Constants
1 For
Compound
czz (MHz)1
ClGeH3
–93.032(15)
FGeH3
–93.03(10)
MeGeH3
3
Cyclopropylmethylgermane
~9 – 10
HCCGeH3
32.5
many calculated quadrupole coupling constants and comparison with experimental data: http://turbo.kean.edu/~wbailey/TOC.html
Cyclopropylmethylsilane (CMS)
gauche
cis
89
trans
Relative
Energy / cm-1
A / MHz
0
629
6625
8726
9728
B / MHz
2612
2222
1987
C / MHz
2287
1983
1962
ma / D
mb / D
mc / D
mtot / D
0.53
0.22
0.13
0.52
0.64
0.76
0.00
0.35
0.00
0.74
0.77
0.77
MP2/6-311+G(d), no ZPE corrections
CMS Experimental Details
• Liquid samples
• Concentration ~1% in ~2.5 atm He/Ne
• Lines split into A and E states, some appear as
“triplets”
• Spectra of all three isotopologues assigned in
natural abundance
• 28Si = 92.2%, 29Si = 4.7%, 30Si = 3.1%
• Consistent only with gauche conformation
• Optimizations performed at MP2/6-311+G(d)
10899.3439
10899.3632
10899.3825
10899.2028
10899.2213
10899.2411
•28Si 404 – 313
•300 scans
10898.5
A
10899
Frequency / MHz
E
10899.5
10900
CMS Fit Using XIAM
28Si
29Si
30Si
A / MHz
8800.5998(9)
8749.8610(21)
8701.3835(21)
B / MHz
2238.6003(6)
2230.8201(9)
2223.2617(9)
C / MHz
2001.0587(6)
1992.4616(7)
1984.1436(7)
DJ / kHz
0.871(10)
0.871 a
0.871 a
DJK / kHz
–7.40(11)
–7.40 a
–7.40 a
dJ / kHz
0.211(3)
0.211 a
0.211 a
V3 / kJ mol–1
6.83(9)
6.82(1)
6.84(1)
F0 / GHz
164(3)
164 a
164 a
Ia / u Å 2
3.09(5)
3.09 a
3.09 a
d / rad
0.745(4)
0.745 a
0.745 a
2.89
4.80
4.73
42
18
18
Parameter
s.d. / kHz
N
a
fixed at 28Si value
CMS Spectroscopic Fitting
Ab Initio
Observed
A / MHz
8726
8800.5998(9)
B / MHz
2222
2238.6003(6)
C / MHz
1983
2001.0587(6)
Ia / u Å2
3.1a
3.09(5)
V3 / kJ mol-1
5.8
6.83(9)
qia / 
43.6
qib / 
47.1
qic / 
83.8
a
Estimate, used as XIAM input
ma / D
47.3(2)
mb / D
90.00 (fixed) mc / D
mtot / D
42.7(2)
Ab Initio Observed
0.22
0.195(2)
0.64
0.674(11)
0.35
0.362(19)
0.77
0.790(13)
Me Group Rotation Barriers in Various Ge and Si Compounds
8
7
-1
Barrier (kJ mol )
6
5
X = Ge
4
X = Si
3
2
1
I
e3
X
M
Br
M
e3
X
C
l
e3
X
M
H
2
e2
X
M
eX
H
2F
M
eX
H
3
M
M
eX
H
2(
C
3H
5)
0
References: see extra slides at end of Powerpoint (too many to fit here!)
Conclusions
• Barriers to rotation comparable to similar species
• Silane barriers typically higher than germane
• B3LYP/6-311++G(3df,3pd) appears to predict 73Ge
quadrupole coupling constants accurately
• Gauche conformer dominates for both CMG and
CMS
• Ab initio energies indicate that higher energy cis
conformer could also be present
Acknowledgements
•?
?
Richard Liberatore
(College of Charleston
summer research
funding)
Barrier to Rotation
V3 / kJ mol-1
Compound
Reference1
X = Ge
X = Si
MeXH2(C3H5)
4.736(6)
6.83(9)
This work
MeXH3
5.18(11)
6.67(20)
Laurie 1959; Kivelson 1954
MeXH2F
3.94(8)
6.52(13)
Roberts 1976; Pierce 1958
Me2XH2
4.945
6.903
Thomas 1969; Niide 2004
Me3XCl
4.45440(3)
6.901(11)
Schnell 2006; Merke 2002
Me3XBr
4.783(12)
--
Schnell 2008
Me3XI
--
7.4151(36)
Merke 2006
1 See
next slide for full references
References for Barrier Comparisons
D. Kivelson, J. Chem. Phys. 22 (1954) 1733.
V. W. Laurie, J. Chem. Phys. 30 (1959) 1210.
I. Merke, W. Stahl, S. Kassi, D. Petotprez, G. Wlodarczak, J. Mol. Spect. 216 (2002) 437.
I. Merke, A. Lüchow, W. Stahl, J. Mol. Struct. 780-781 (2006) 295.
Y. Niide, M. Hayashi, J. Mol. Spect. 223 (2004) 152.
L. Pierce, J. Chem. Phys. 29 (1958) 383.
R. F. Roberts, R. Varma, J. F. Nelson, J. Chem. Phys. 64 (1976) 5035.
M. Schnell, J.-U. Grabow, Phys. Chem. Chem. Phys. 8 (2006) 2225.
M. Schnell, J.-U. Grabow, Chem. Phys. 343 (2008) 121.
E. C. Thomas, V. W. Laurie, J. Chem. Phys. 50 (1969) 3512.
Table 3.6: Dipole moment data for the 72Ge isotopomer.
Transition
Dn / E2(calc) a)
(105 MHz cm2 / V2)
Dn / E2(obs)
MHz cm2 / V2)
110 ← 101 |M| = 1
1.7040
1.7047
-0.04
111 ← 000 |M| = 1
0.3712
0.3697
0.40
212 ← 101 |M| = 1
0.5771
0.5745
0.45
211 ← 101 |M| = 1
0.7250
0.7256
-0.09
303 ← 202 |M| = 2
0.4403
0.4406
-0.06
211 ← 202 |M| = 2
1.1819
1.1759
0.51
312 ← 303 |M| = 2
0.4012
0.39622
1.25
312 ← 303 |M| = 3
1.0912
1.0998
-0.79
(105
%
Difference b)
ma = 0.1782(10) D
mb = 0.581(4) D
mc = 0.305(9) D
mtotal = 0.680(5) D
a)
b)
“Dn / E2(calc)” is the Stark coefficient obtained from a second-order perturbation theory calculation, using the fitted rotational constants given in Table 3.1.
“% Difference” is obtained from “Dn / E2(calc)” – “Dn / E2(obs)”
Table 3.7: Kraitchman single isotopic substitution coordinates (germane). All errors are to ±0.0001Å.
70Ge
72Ge
73Ge
76Ge
Ab initio
|a| / Å
0.6241
0.6241
0.6239
0.6241
0.6336
|b| / Å
0.3440
0.3441
0.3442
0.3439
0.3437
|c| / Å
0.0504
0.0500
0.0495
0.0508
0.0543
Silane Dipole Data
Squared Dipole Component
A
0.03788 +/B
0.45427 +/C
0.13118 +/Total
Transition
|M|
Dipole Component
0.00089
0.19462
0.01445
0.67399
0.01366
0.36219
0.78951
Observed
+/+/+/+/-
0.00230
0.01072
0.01886
0.01261 Debyes
Calculated
Obs-Calc
Percent
1( 1, 1) -
0( 0, 0)
0
0.33713E-05
0.33771E-05
-0.57294E-08
-0.17
2( 1, 2) -
1( 0, 1)
1
0.61687E-05
0.62217E-05
-0.53016E-07
-0.86
2( 1, 1) -
1( 0, 1)
1
0.79953E-05
0.80473E-05
-0.52030E-07
-0.65
1( 1, 0) -
0( 0, 0)
0
0.37446E-05
0.37914E-05
-0.46820E-07
-1.25
1( 1, 0) -
1( 0, 1)
1
0.19721E-04
0.19655E-04
0.66051E-07
0.33
1( 1, 1) -
1( 0, 1)
1
-0.56754E-05
-0.57369E-05
0.61504E-07
-1.08
0.51459E-07
0.82
RMS