Transcript p081 tHTE 07 PC.ppt

ANALYSIS OF ROTATIONAL
STRUCTURE IN THREE C-TYPE BANDS
IN THE HIGH-RESOLUTION INFRARED
SPECTRUM OF
trans,trans-1,3,5-HEXATRIENE
NORMAN C. CRAIG, MATTHEW C. LEYDEN, and AMIE K.
PATCHEN,Department of Chemistry and Biochemistry, Oberlin College,
Oberlin, OH 44074, USA [email protected]
TONY MASIELLO, Environmental and Molecular Sciences Laboratory,
Pacific Northwet National Laboratory, P. O. Box 999, Mail Stop k8-88,
Richland, WA 99352
1,3-Butadiene
Blue: re structure. N. C. Craig, P. Groner, D. C. McKean, J. Phys.
Chem. A, 2006, 110, 8044-8059.
Red: localized C=C and sp2-sp2 bond lengths.
cis- and trans-1,3,5-Hexatriene
B3LYP/cc-pVTZ Model
Synthesis
P2O5
R.T.
OH
20% yield
GC separation
P2O5
60oC
OH
20% yield
IR Spectrum of trans-Hexatriene at 0.1 cm-1 resolution.
C3
C1
C2
Spectroscopy – PNNL
Bruker IFS 125HR
Resolution: 0.0013 cm -1
-1
Doppler width for hexatriene at 900 cm :
-1
0.0012 cm
White cell: 19.2 m
Pressure: 0.15 Torr (C1, C2); 0.27 Torr (C3)
No. scans: 320 (C 1, C2); 256 (C3)
Absorbance Spectrum of transHexatriene
C1
C3
C2
C1 Band in Absorbance
C1 Band - Detail of Subband Assignments in R the
Branch
Center of C1 Band
0.25
0.2
Calculated
Absorbance
0.15
0.1
0.05
0
898
899
900
901
902
903
Wavenumber
Observed
C2 Band in Absorbance
C3 Band in Absorbance
Loomis-Wood Display for Part
of the C3 Band
Loomis-Wood Display of RR7,
RR , and RR Subbands in the C
8
9
3
Band
Rotational Constants
Conclusions
• Rotational analysis of nonpolar trans-hexatriene depends on highresolution (0.0013 cm-1) infrared spectroscopy.
• Rotational structure in 3 C-type bands has been analyzed.
• Hot bands from the torsional mode at 94 cm-1 and the in-plane
bend at 152 cm-1 cause congested spectra.
• GS rotational constants from GSCDs of 14(au) at 1011 cm-1, 16(au)
at 901 cm-1, and 17(au) at 683 cm-1 taken together are reported.
• US rotational constants are reported for 16(au) at 901 cm-1.
• First step toward an equilibrium structure for trans-hexatriene.
• Various carbon-13 and deuterium isotopomers must be made, and
their rotational constants found.
Support
• Dreyfus Foundation.
• Pacific Northwest National Laboratory
Operated by Battelle as a DOE Contractor.
• Oberlin College