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Analysis of the Rotational Structure in the High-Resolution Infrared Spectrum of trans-Hexatriene-1,1-d2 and -cis-1-d1
Norman C. Craig, Hannah A. Fuson, and Hengfeng Tian Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH
44074, USA [email protected]
Thomas A. BlakeEnvironmental Molecular Sciences Laboratory, Pacific Northwest National
Laboratory, Richland, WA 99352
Goal
Do the isomers of hexatriene (HTE) show greater structural effects of -electron delocalization than does butadiene?
Preliminary data for the C6 backbone of cis-HTE say “Yes,” as do B3LYP calculations with a cc-pVTZ basis set.
New work: analysis of C-type bands in high-resolution IR spectra of trans-HTE-1,1-d2 and -cis-1-d1.
Method: Semi-Experimental Equilibrium Structure
• Obtain ground state rotational constants from the rotational structure in high-resolution IR bands. (Nonpolar trans-HTE is MW silent.)
• Do so for a full series of isotopologues.• Use quantum chemistry (triple zeta level) to compute
vibration-rotation constants (alphas). • Find equilibrium rotational constants (k = a,b,c)
• Obtain an re structure from a global fit of all the equilibrium rotational constants.
Be, k B0, k 1/ 2 k,i1
n
Synthesis
IR spectrum (0.1 cm-1 resol.) of trans-HTE-1,1-d2 and -cis-1-d1
d2
d2
d2
d1
C-Type Bands Analyzed
tHTE-1,1-d2
29 (902 cm-1) CH2 out-of-plane flapping
31 (722 cm-1) CD2 out-of-plane flapping
tHTE-cis-1-d1
31 (803 cm-1) CD out-of-plane flapping
C-type Band (0.0015 cm-1 resol.) of trans-HTE-1,1-d2
Detail of C-type Band at 902 cm-1 of trans-HTE-1,1-d2
Finer Detail of C-type Band at 902 cm-1
C-type Band (0.0015 cm-1 resol.) of trans-HTE-1,1-d2
Rotational Constants for trans-Hexatriene-1,1-d2 Ground state 29(a") C-type
902 cm-1 A/cm-1 0.801882(1) 0.795541(4) B/cm-1 0.041850(2) 0.041881(2) C/cm-1 0.039804(1) 0.039767(2)
J 1010/cm-1 0.9218a 0.9218a
K 108/cm-1 0.9723a 0.9723a
K 106/cm-1 1.837(2) 1.837b
JK 108/cm-1 -2.65(5) -2.65b
J 109/cm-1 1.62(4) 1.671(4) -0.9946 -0.9944 0/cm-1 902.05
std. dev./cm-1 0.00033 0.00042 c/amu Å2 -0.3223 -0.2064
No. trans. 980d 292 Ka' 5-22e, 8-19f 5-7 Jmax 95 85
a Calculated with the B3LYP/cc-pVTZ model. b Ground state values. c Inertial defect, = Ic - Ia
- Ib. d 599 GSCDs from the 902 cm-1 band; 381 from the 722 cm-1 band. e 902 cm-1 band ( 29). f 722 cm-1 band ( 31).
C-type Band (0.0015 cm-1 resol.) of trans-HTE-cis-1-d1
Loomis-Wood Display for C-type Band of trans-Hexatriene-cis-1-d1
• RR13 yellow RR16 blue
• RR14 magenta RR17 brown
• RR15 red
Rotational Constants for trans-Hexatriene-cis-1-d1
Ground state 31(a") C-type
803 cm-1 A/cm-1 0.809388(1) 0.8053839(9) B/cm-1 0.043532(2) 0.0435516(8) C/cm-1 0.041319(1) 0.0412748(9)
J 1010/cm-1 1.0870a 1.0870a
K 108/cm-1 1.0844a 1.0844a
K 106/cm-1 2.150(2) 1.901(5)
JK 108/cm-1 -3.03(4) -2.61(2)
J 109/cm-1 1.67(4) 1.666(3) -0.99424 -0.99404 0/cm-1 803.01823(3)
std. dev./cm-1 0.00035 0.00038 b/amu Å2 -0.093759 0.420146
No. trans. 893 1409 Ka' 3-21 3-14 Jmax 94 98
a Calculated with the B3LYP/cc-pVTZ model. b Inertial defect, = Ic - Ia
- Ib.
ConclusionsAnalysis of the rotational structure in the high-resolution
(0.0015 cm-1) infrared spectrum of two C-type bands of trans-hexatriene-1,1-d2 and of a C-type band of trans-hexatriene-cis-1-d1 has yielded ground state rotational constants for the two species.
Prior work gave ground state rotational constants for the normal species.1
Good progress has been made toward the rotational constants needed for a semi-experimental structure of trans-hexatriene. See the following talk.
1. N. C. Craig, M. C. Leyden,M. C. Moore, Amie K. Patchen, T. van den Heuvel, T. A. Blake, T.
Masiello, R. L. Sams J. Mol. Spectrosc. 2010, 262, 49-60.
Support
Dreyfus Foundation
Environmental and Molecular Sciences Laboratory, PNNL
National Science Foundation
Oberlin College