1. Gas Phase Conformational Distributions
for the 2-Alkylalcohols 2-Pentanol
and 2-Hexanol
from Microwave Spectroscopy
M. J. Tubergen, A. R. Conrad, R. E. Chavez III, I. Hwang
Department of Chemistry, Kent State University
R. D. Suenram, J. J. Pajski, B. H. Pate
Department of Chemistry, University of Virginia

2. Alkenes: 1-pentene through 1-dodecene
Background
1-heptanal
13 conformational isomers
J. M. Fisher et al. J. Mol. Struct. 795 (2006) 143.
Alkenes: 1-pentene through 1-dodecene
1-pentene
1-octene
Spectra from 4 (of 5)
conformation isomers
Spectra from 15 (of 131)
conformational isomers

3. Alkanes 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 (1996)
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.
Microwave Studies of 2-Methylpentane
R. K. Bohn
RH04, Thursday 2:16 p.m.

4. 2-Butanol 2-Butanol Complexes
DE = 2.9 kJ mol-1
DE = 3.4 kJ mol-1
DE = 0 kJ mol-1
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. 205 (2001) 38.
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, J. Mol. Spectrosc. 214 (2002) 97.
A.K. King and B.J. Howard, Chem. Phys. Lett. 348 (2001) 343.

5. Kent State FTMW Range: 10 – 24 GHz Resolution: < 2 kHz
Repetition Rate: Hz
Scan Rate: 600 MHz / day

6. UVa Chirped Pulse Broadband (no cavity) 7.5 – 18.5 GHz.
G.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 ms 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 kHz
Precision: ~ 10 kHz
10000 cycle average takes ~ 26 minutes
Equivalent to 10 – 30 pulse average of comparable cavity instrument.

7. Broadband Spectra

8. 2-pentanol spectral fitting
relative
intensity 10 3 1

9. 2-hexanol spectral fitting

10. 2-hexanol spectral fitting

11. Structural Configurations
Definition of Conformational Structures
aa – a
a: 180º
g: +60º
g’: -60º
t1t2 – w
t1t2t3 – w
aaa – a

12. Model Conformations of 2-Pentanol
MP2/ G**
27 unique conformations

13. Model Conformations of 2-Hexanol
MP2/ G**
75 unique conformations

14. Comparison to Model Structures
DIrms 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.

15. 2-Pentanol Comparisons
(%DI)rms
DE / kJ mol-1
ma / D
mb / D
mc / D
Conformer 1 (mc > mb > ma)
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
g’a – a
1.87
2.8
-0.18
1.71
-0.78
Conformer 2 (ma > mc > mb)
0.44
g’a – g
0.69
3.6
1.35
1.10
1.01
0.77
1.39
Conformer 3 (ma > mc > mb)
0.35
0.85
1.55
1.93

16. 2-Hexanol Comparisons (%DI)rms DE / kJ mol-1 ma / D mb / D mc / D
Conformer I (ma > mc > mb)
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 (ma > mc > mb)
0.36
0.88
1.61
1.89
Conformer III (ma > mc > mb)
0.38
g’aa – g
0.52
3.3
1.44
0.87
1.12
0.61

17. 2-Hexanol Comparisons (%DI)rms DE / kJ mol-1 ma / D mb / D mc / D
Conformer VI (ma > mb > mc)
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
g’ag – g
1.82
6.2
1.13
1.43
0.98
Conformer XIV (ma >> mb ~ mc ~ 0)
0.42
1.04
1.15
1.29
1.59
1.89

18. H e x a n o l C m p r i s (%DI)rms DE / kJ mol-1 ma / D mb / D mc / D
Conformer IV (ma > mc > mb)
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 (ma >> mc > mb ~ 0)
0.76
0.79
1.19
gaa – g’
3.5
-0.62
-0.19
1.69
1.41
1.59
gaa – g
1.88
5.7
-1.34
-0.03

19. Conformational Assignment
2-Pentanol 1
aa – a 2
g’a – g’ 3
aa – g’ 4
ag – a
2-Hexanol I
aaa – a
aaa – g’ II
III
g’aa – g’
g’aa – g IV
aag – a
g’ag’ – g V
aga – a VI
aag’ – a
VII
gaa – a
gaa – g
VIII
aga – g’ IX
g’ag’ – g’ X
g’g’a – g’ XI
g’aa – a
aaa – g
XII
XIII
g’ag – g’
aag’ – g’
XIV

20. Acknowledgments National Science Foundation
(CHE and CHE )
Ohio Supercomputer Center
National Science Foundation Major Resource
Instrumentation Program ( )