Transcript DFBD Isomers Cols 09_PC.ppt

ANALYSIS OF THE ROTATIONAL STRUCTURE
IN A C-TYPE BAND IN THE HIGH-RESOLUTION
INFRARED SPECTRUM OF trans,trans-1,4DIFLUOROBUTADIENE-1-d1
Norman C. Craig, Christopher F. Neese, and
Deacon J. Nemchick, Department of Chemistry
and Biochemistry, Oberlin College, Oberlin, OH
44074 [email protected]
Michael Lock, Physikalisch-Chemisches Institut
der Justus Liebig Universität, Heinrich-Buff Ring
58, Giessen D-35392, Germany
Outline
• This talk has been recast as a progress report on
obtaining rotational constants needed for
determining semi-experimental equilibrium
structures of the isomers of 1,4-difluorobutadiene
(DFBD).
• Two new high-resolution IR spectra have been
recorded since the abstract was submitted.
• Analyses of the rotational structure in C-type
bands for three deuterium isotopomers of
trans,trans-DFBD and cis,cis-DFBD are reported.
Acknowledgment
Dr. Robert Sams of the Environmental
and Molecular Sciences Laboratory at
Pacific Northwest National Laboratory
recorded IR spectra of the 2-d1 species
of the trans,trans and cis,cis isomers on
a Bruker HR125 spectrometer at 0.0015
cm-1 resolution.
Semi-Experimental Equilibrium Structure
for cis,trans-1,4-Difluorobutadiene?a
17-parameter (9 bond lengths, 8 bond angles)
problem
MW spectra for normal, 4 13C species, and 5 2H
species.
C2 from the trans end lies very close to the a
axis; B0 for the 2-d1 species is anomalously
large; problems in fitting the C2H2 bond
parameters.
aN.
C. Craig, P. Groner, D. C. McKean, M. J. Tubergen, Int. J. Quant.
Chem. 2003, 95, 837-852.
Magenta RR6
Red RR7
Yellow RR8
Green RR9
Blue RR10
Brown RR11
Magenta PP6
Red PP7
Green PP8
Blue PP9
Yellow PP10
Brown PP11
Grey PP12
Orange PP13
Spectrum of cis,cis-DFBD-1-d1 and an
Improved Spectrum of trans,trans-DFBD-1-d1
• HFC=CH2 has been exchanged to
DFC=CH2 with NaOD/D2O at 120°C for
many days in a quartz vessel. By the
chemistry used to prepare the 2-d2
isotopomers from HFC=CD2, the two 1d1 isotopomers should be accessible.
Magenta RR10
Red RR11
Yellow RR12
Green RR13
Blue RR14
Brown RR15
Grey RR16
Orange RR17
Summary of High-Resolution IR Bands Analyzed to Determine
the Ground State Rotational Constants of the trans,trans and
cis,cis Isomers of 1,4-Difluorobutadiene.
Species
normala
1-d1
2-d1
1,4-d2
1-13C1 or 1,4 -13C2
2-13C1 or 2,3 -13C2
a
trans,trans
2C, 1A
1C
Exploratory (4C)
1C
cis,cis
2C
1C and more
N. C. Cra ig, M. C. Moore, C. F. Neese, D. C. Oerte l, L. Pedraza, and T.
Masiello, J. Mol. Spectrosc. 2009, 254, 39-46.
Conclusions
The semi-experimenta l equilibrium structure for the cis,trans isomer of
1,4-difluorobutadiene derived from MW spectroscopy remains in doubt.
A near "on-axis" carbon atom compromis es the structure fit.
Ground state rotational constants are known for the normal species of
the cis,cis and trans,trans isomers from the analysis of high-resolution
IR spectra.
Preliminar y analyses of the rotational structure in several IR bands of
deuterium isotopomers exist for trans,trans-1-d1, trans,trans-1,4-d2, and
cis,cis-2-d1. High-resolution IR spectra of the trans,trans-2-d1 species
have been recorded and essayed.
Preparation of 1-fluoroethylene -1-d1 by exchange promises a spectrum
of cis,cis-DFBD-1-d1 and an improved spectrum of trans,trans-DFBD-1d 1.
The method used for making the deuterium isotopomers is impractical
for the 13C isotopomers. A new synthetic strategy is being developed
for making the 13C isotopomers.
Funding
National Science Foundation (Beowulf
cluster supercomputer)
Dreyfus Foundation
Pacific Northwest National Laboratory
Department of Chemistry and Biochemistry,
Oberlin College