Gas Phase Conformational Distributions for the 2-Alkylalcohols 2-Pentanol and 2-Hexanol from...
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Transcript of Gas Phase Conformational Distributions for the 2-Alkylalcohols 2-Pentanol and 2-Hexanol from...
Gas Phase Conformational Distributionsfor the 2-Alkylalcohols 2-Pentanol
and 2-Hexanolfrom Microwave Spectroscopy
M. J. Tubergen, A. R. Conrad, R. E. Chavez III, I. HwangDepartment of Chemistry, Kent State University
R. D. Suenram, J. J. Pajski, B. H. PateDepartment of Chemistry, University of Virginia
OC H 2 B a s eO
P O H H H HH5 ' OC H 2 B a s eOP O H H H HHP 1 '2 '3 'OO O
O O O --
-4 '
1-heptanal
13 conformational isomers
J. M. Fisher et al. J. Mol. Struct. 795 (2006) 143.
Alkenes: 1-pentene through 1-dodecene
Spectra from 4 (of 5) conformation isomers
Spectra from 15 (of 131) conformational isomers
1-pentene 1-octene
Background
Gauche kinks add ~ 2.5 kJ mol-1 to the energy
L. S. Bartell and D. A. Kohl, J. Chem. Phys. 39 (1963) 3097.
G. D. Smith and R. L. Jaffe, J. Phys. Chem. 100 (1996) 18718.
CCSD(T)/cc-pVTZ//MP2/6-311G(2f,p)
Microwave spectra of anti-anti and anti-gauche configurations:
G. B. Churchill and R. K. Bohn, J. Phys. Chem. A 111 (2007) 3513.
Alkanes
Microwave Studies of 2-MethylpentaneR. K. Bohn
RH04, Thursday 2:16 p.m.
2-Butanol
Microwave spectrum for each of the carbon backbone configurations.Hydroxyl orientation inferred from observed dipole selection rules.
A.K. King and B.J. Howard, J. Mol. Spectrosc. 214 (2002) 97.
2-Butanol Complexes
Argon-2-butanol and (2-butanol)2 complexes have the anti configuration of the carbon backbone.
A.K. King and B.J. Howard, Chem. Phys. Lett. 348 (2001) 343.
A.K. King and B.J. Howard, J. Mol. Spectrosc. 205 (2001) 38.
E = 2.9 kJ mol-1E = 3.4 kJ mol-1E = 0 kJ mol-1
UVa Chirped PulseG.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, B.H. Pate
J. Mol. Spectrosc. 238 (2006) 200.
Broadband (no cavity) 7.5 – 18.5 GHz.
1 s long chirped pulse. 1 kW pulsed traveling wave tube amplifier.
Broadcast/detection with WRD750 standard gain horns.
Amplified & downconverted. Digitized at 40 GS / s.
Resolution: 40 kHzPrecision: ~ 10 kHz
10000 cycle average takes ~ 26 minutesEquivalent to 10 – 30 pulse average of comparable cavity instrument.
Broadband Spectra
6.5 8.5 10.5 12.5 14.5 16.5 18.5
Frequency (G H z)
H exanol Experim ental B roadband Spectrum
Pentanol Experim ental B roadband Spectrum
Pentanol C onform er I S im ulation
H exanol C onform er I S im ulation
rotationalparameter
1 2 3 4
A / MHz 7224.557 (3)a 7027.907 (2) 7238.730 (5) 5944.849 (3)
B / MHz 1741.198 (1) 1720.8889 (7) 1727.313 (2) 2003.4287 (9)
C / MHz 1513.558 (1) 1486.0273 (8) 1499.861 (2) 1833.164 (1)
J / kHz 0.15 (1) 0.14 (2) 0.20 (4) 0.70 (3)
JK / kHz 1.58 (5) 1.69 (7) 1.7 (2) 5.9 (2)
K / kHz 3.7 (7) 0d 0d 0d
J /kHz 0.018 (5) 0d 0d 0d
K / kHz 1.3 (4) 0d 0d 0d
N 52 32 21 38
/ kHz 8.4 8.7 14.7 12.4
selection rulese c > b > a a > c > b a > c > b c > a > b
configuration aa - a g’a - g’ aa - g’ ag - aconfiguration aa - a g’a - g’ aa - g’ ag - a
2-pentanol spectral fitting
relativeintensity
10 33 1
2-hexanol spectral fittingrotationalparameter
A / MHz
B / MHz
C / MHz
I II III IV V VI VII
6611.3383(7)a
6618.766(1)
6418.576(2)
5169.271(1)
5465.031(2)
5386.535(4)
5196.2729(8)
1011.56061(4)
1004.6000(1)
997.9263(3)
1132.6212(6)
1156.6301(6)
1152.2818(5)
1095.8890(3)
926.57241(6)
918.9220(1)
910.1749(3)
1083.1574(6)
1095.7891(6)
1008.5955(5)
1057.1206(2)
J / kHz
JK / kHz
K / kHz
J /kHz
K / kHzK / kHz
0.0543 (2) 0.0490 (6) 0.0479 (8) 0.186 (1) 0.235 (2) 0.106 (2) 0.139 (1)
0.886 (1) 0.693 (3) 0.807 (4) 0.794 (7) 2.86 (1) -0.25 (2) 1.73 (3)
2.7 (1) 2.6 (2) 1.1 (4) 4.6 (3) 3.2 (4) 5.6 (8) 0d
0.00539 (5) 0.0056 (3) 0.00601 (3) -0.0187 (7) 0.0237 (8) 0.0227 (9) 0.0012 (8)
0.50 (1) 0.51 (5) 0.5 (1) -4.7 (3) -1.7 (3) 0.4 (2) 0d
N
/ kHz
selection rulese
configuration
89 53 42 37 34 26 24
1.7 1.8 1.9 2.2 2.3 2.2 2.6
a > cb a > cb a > cb a > cb a > cb a > b > c a >> b >c ~ 0
aaa (-a or -g’)
aaa (-a or -g’)
g’aa - g’ aag - ag’ag’ - g
aga - a aag’ - a gaa (-a or -g)
2-hexanol spectral fitting
VIII IX X XI XII XIII XIV
5478.901 (5) 5118.538(3)
5302.463(6)
6380.0804(8)
6533.5516(8)
5296.26(9)
5394.22(7)
1150.0356(5)
1118.1438 (7)
1143.8617(7)
1003.1223(2)
1006.9431(2)
1139.5507 (6)
1142.153(1)
1087.9091(5)
1057.6387 (7)
1077.4456(5)
914.0581(2)
923.3035(2)
996.2448(6)
1001.502(1)
0.227 (2) 0.140 (1) 0.184 (2) 0.0483 (5) 0.056 (1) 0.077 (1) 0.098 (6)
2.48 (1) 0.42 (1) 2.01 (4) 0.872 (4) 0.85 (2) -0.2 (1) -0.25 (4)
0d 4.4 (5) 0d 1.8 (2) 0d 0d 0d
0.026 (2) 0d 0.016 (2) 0.0065 (2) 0.0056 (8) 0d 0d
0d -1.3 (3) 0d 0.63 (7) 0d 0d 0d
rotationalparameter
A / MHz
B / MHz
C / MHz
J / kHz
JK / kHz
K / kHz
J /kHz
K / kHzK / kHz
N
/ kHz
selection rulese
configuration
21 26 17 23 14 10 12
2.4 2.7 2.4 0.7 2.1 3.1 4.7
a >> b >c ~ 0
a >> c >b ~ 0
a >> b >c ~ 0
b > c >>a ~ 0
b > c
>> a ~ 0a >> b ~
c ~ 0a >> b ~
c ~ 0
aga - g’ g’ag’ - g’ g’g’a - g’ g’aa - aaaa - g
aaa - gg’aa - a
g’ag - g’aag’ - g’
aag’ - g’g’ag - g’
Structural Configurations
Definition of Conformational Structures
O
12
34 6
H
O
12
34
5
H
5
1 = C1 - C2 - C3 - C4
3 = C3 - C4 - C5 - C6
= H - O - C2 - C3
1 = C1 - C2 - C3 - C4
2 = C2 - C3 - C4 - C5
2 = C2 - C3 - C4 - C5
= H - O - C2 - C3
a: 180ºg: +60ºg’: -60º
12 – 123 –
aaa – a
aa – a
Model Conformations of 2-Pentanol
configuration1122 -
E / kJ mol-1-1 rel. pop. A / MHz B / MHz C / MHz
aa - a 0.0 1.00 7275.0 1746.8 1517.7
aa - g’ 1.0 0.68 7282.8 1728.9 1500.4
ag - a 1.7 0.51 5988.4 2050.1 1869.9
aa -g 1.9 0.48 7147.6 1730.9 1510.5
g’a - g’ 2.1 0.44 7056.2 1731.0 1490.0
g’a - a 2.8 0.33 7011.2 1740.3 1496.6
ag - g’ 3.2 0.28 5981.6 2013.3 1839.7
ag - g 3.2 0.28 5892.8 2026.9 1854.0
g’a - g 3.6 0.24 6956.1 1729.6 1490.9
ga - g’ 3.8 0.22 6179.0 1888.1 1707.5
MP2/6-311++G**27 unique conformations
Model Conformations of 2-Hexanol
MP2/6-311++G**75 unique conformations
configuration112233 -
E / kJ mol-1-1 rel. pop. A / MHz B / MHz C / MHz
aaa - a 0.0 1.00 6655.7 1014.3 928.7
aaa - g’ 0.7 0.74 6659.7 1005.4 918.9
aga - a 1.5 0.56 5519.9 1180.0 1114.7
g’aa - g’ 1.8 0.48 6446.0 1002.7 911.9
aaa - g 1.9 0.47 6549.7 1006.1 924.1
aag’ -a 2.3 0.40 5386.6 1162.5 1015.6
aag - a 2.4 0.39 5195.4 1143.6 1083.7
g’aa - a 2.6 0.36 6411.2 1006.7 915.6
aga - g’ 2.8 0.33 5517.3 1161.7 1098.2
agg - a 2.9 0.32 4161.2 1440.7 1320.5
Comparison to Model Structures
2 2 2
42 ,exp ,mod ,exp ,mod ,exp ,mod
,exp ,exp ,exp
I I I I I I10% I
3 I I Ia a b b c c
rmsa b c
Irms biases towards model structures that best reproduce Ib and Ic (largest I’s).
Uncertainty in the principal axis coordinates of ab initio models propagates as relative errors into calculated values for moments of inertia.
2-Pentanol Comparisons(%I)rms E / kJ mol-1 a / D b / D c / D
Conformer 1 (c > b > a)
aa – a 0.47 0.0 -1.23 -0.91 0.96
aa – g 0.72 1.9 -0.23 -1.59 0.81
aa – g’ 0.80 1.0 1.64 -0.60 0.98
g’a – g’ 1.69 2.1 1.80 0.15 0.81
g’a – a 1.87 2.8 -0.18 1.71 -0.78
Conformer 2 (a > c > b)
g’a – g’ 0.44 2.1 1.80 0.15 0.81
g’a – g 0.69 3.6 1.35 1.10 1.01
g’a – a 0.77 2.8 -0.18 1.71 -0.78
aa – g 1.39 1.9 -0.23 -1.59 0.81
Conformer 3 (a > c > b)
aa – g’ 0.35 1.0 1.64 -0.60 0.98
aa – g 0.85 1.9 -0.23 -1.59 0.81
aa – a 0.98 0.0 -1.23 -0.91 0.96
g’a – g’ 1.55 2.1 1.80 0.15 0.81
g’a – a 1.93 2.8 -0.18 1.71 -0.78
2-Hexanol Comparisons(%I)rms E / kJ mol-1 a / D b / D c / D
Conformer I (a > c > b)
aaa – a 0.44 0.0 -1.28 -0.83 0.98
aaa – g 0.64 1.9 0.06 -1.68 -0.81
aaa – g’ 0.73 0.7 1.63 -0.79 0.91
g’aa – g’ 1.82 1.8 -1.82 -0.45 0.72
g’aa – a 1.95 2.6 -0.02 1.66 0.70
Conformer II (a > c > b)
aaa – g’ 0.36 0.7 1.63 -0.79 0.91
aaa – g 0.70 1.9 0.06 -1.68 -0.81
aaa – a 0.88 0.0 -1.28 -0.83 0.98
g’aa – g’ 1.61 1.8 -1.82 -0.45 0.72
g’aa – a 1.89 2.6 -0.02 1.66 0.70
Conformer III (a > c > b)
g’aa – g’ 0.38 1.8 -1.82 -0.45 0.72
g’aa – g 0.52 3.3 1.44 0.87 1.12
g’aa – a 0.61 2.6 -0.02 1.66 0.70
2-Hexanol Comparisons
(%I)rms E / kJ mol-1 a / D b / D c / D
Conformer VI (a > b > c)
aag’ – g’ 0.25 3.3 -1.82 0.35 0.85
aag’ – a 0.65 2.3 1.00 1.11 0.88
aag’ – g 0.70 4.1 -0.54 1.48 -0.86
g’ag – g’ 1.06 4.7 -1.92 0.04 0.67
g’ag – a 1.34 5.3 0.41 1.60 0.85
g’ag – g 1.82 6.2 1.13 1.43 0.98
Conformer XIV (a >> b ~ c ~ 0)
aag’ – g’ 0.42 3.3 -1.82 0.35 0.85
g’ag – g’ 1.04 4.7 -1.92 0.04 0.67
aag’ – g 1.15 4.1 -0.54 1.48 -0.86
aag’ – a 1.29 2.3 1.00 1.11 0.88
g’ag – a 1.59 5.3 0.41 1.60 0.85
g’ag – g 1.89 6.2 1.13 1.43 0.98
(%I)rms E / kJ mol-1 a / D b / D c / D
Conformer IV (a > c > b)
aag – a 0.62 2.4 1.28 -0.78 -0.99
aag – g 0.64 4.2 -0.49 -1.69 0.45
aag – g’ 0.85 3.0 -1.55 -0.22 -1.32
g’ag’ – a 1.24 4.5 -0.34 1.77 -0.41
g’ag’ – g’ 1.37 3.7 1.72 0.08 -1.10
g’ag’ – g 1.62 5.3 1.48 0.96 1.01
g’g’a – g 1.84 5.0 1.16 0.46 1.53
gaa – a 1.87 3.6 1.20 1.30 0.35
Conformer IX (a >> c > b ~ 0)
g’ag’ – g’ 0.76 3.7 1.72 0.08 -1.10
g’ag’ – g 0.79 5.3 1.48 0.96 1.01
g’ag’ – a 1.16 4.5 -0.34 1.77 -0.41
gaa – a 1.19 3.6 1.20 1.30 0.35
gaa – g’ 1.30 3.5 -0.62 -0.19 1.69
aag – g’ 1.41 3.0 -1.55 -0.22 -1.32
aag – g 1.59 4.2 -0.49 -1.69 0.45
gaa – g 1.88 5.7 -1.34 1.53 -0.03
Hexanol Comparisons
Conformational Assignment
1aa – a
2g’a – g’
3aa – g’
4ag – a
Iaaa – aaaa – g’
IIaaa – g’aaa – a
IIIg’aa – g’g’aa – g
IVaag – a
g’ag’ – g
Vaga – a
VIaag’ – a
VIIgaa – agaa – g
VIIIaga – g’
IXg’ag’ – g’
Xg’g’a – g’
XIg’aa – aaaa – g
XIIaaa – gg’aa – a
XIIIg’ag – g’aag’ – g’
XIVaag’ – g’g’ag – g’
2-Hexanol
2-Pentanol
Acknowledgments
National Science Foundation (CHE-0240168 and CHE-0616660)
Ohio Supercomputer Center
National Science Foundation Major Resource Instrumentation Program (0215957)