La molecola

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Conformation analysis Liquid Crista
G. Pileio.
Dipartimento di Chimica, Università della
Calabria, Italy.
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of Styrene dissolved in lline phases.
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The Molecule and the Spectrum
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Introduction
The planarity of Styrene and is probable
planarity was the subject of more both
spectroscopic and theoretical work1. Bcause of
the role of LXNMR in the study of conformational
equilibria in liquid-like solvents2, we propose
this work to study the molecule in tree nematic
pheses. With this purpose we register and
analyse, thanks to proton data in literature3,
the spectra of styrene-a-13C and styrene-ß-13C in
the tree phases ZLI1132, I35 and a 4555 mixture
of ZLI1132 and EBBA. The dipolar couplings coming
from, are used to investigate the structure and
the conformation of the molecule. The
introduction of the C-H couplings, as we can see,
lead to a more accurate conformational analysis
but open the problem of vibrational
contributions. The situation turn complex by the
possibility of a distortion in the structur as
noted in this work. Finally, the approach used
for the conformationa distribution function is
that recently introduced in a work accepted for
publication4.
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Vibrational Contibutions
Covariance Matrix
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Calculations
In the following calculations we use the new
approach4 to treat the conformational
distributions by using a direct description of
probability function in terms of a gaussian
function.
Dipolar couplings came from the analysis of the
spectra of styrene-a-13C and styrene-ß-13C in the
three nematic phases ZLI1132, I35 and 4555
ZLI1132/EBBA. Similar results have been obtained
using the standard Fourier expression depicted in
the theory.
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Table 1
from the optimization of -ene fragment and kept
fixed kept fixed from 1
fixed. Geometrical parameters of the ring were
also optimizad but not reported. They are in
agreement with standard values.
In Table 1 RMS, potential and geometrical
parameters are reported, allowing the torsional
angle to vary in column B and C, keeping it at 0
in column B and C. In A the geometrical values
from reference 1 are reported for comparison.
The data obtained in the other phases are not
reported since no significant differences were
observed.
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Table 2
from the optimization of -ene fragment and kept
fixed kept fixed from 1
fixed. Geometrical parameters of the ring were
also optimizad but not reported. They are in
agreement with standard values.
In Table 2 RMS, potential and geometrical
parameters are reported, allowing the torsional
angle to vary in column B and C, keeping it at 0
in column B and C. In A the geometrical values
from reference 1 are reported for comparison.
Note that in column C and C we introduce the
optimization of the dihedral angle of the two
enes protons.
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Considerations and References

• Data coming from each isotopomer can not
  discriminate between planar or ene out of
  ring-plane minimum structure.
• The use of the two set from the two isotopomer
  in the same phase let dicriminate in favour of
  ene out of ring-plane.
• The need to introduce out of plane deformations
  for the ene fragment in order to fit the data is
  questionable and subject of further studies.

1 J. C. Cochran, K. Hagen, G. Paulen, Q. Shen,
S. Tom, M. Traetteberg, C. Wells, J. Mol.
Struct., 413- 414, 1997, 313-326. 2 J.
W. Emsley, Encyclopedia of NMR , Ed. D. M.
Grant and R. K. Harris, Wiley, New York,
1996. 3 J. W. Emsley and M. Longeri, Mol.
Phys., 42, 2, 1981, 315-328. 4 J. W. Emsley, G.
R. Luckhurst, C. P. Stockley, Proc. R. Soc. Lond.
A, 381, 1982, 117. 5 S. Sýkora, J. Vogt, H.
Bösinger and P. Diehl, J. Magn. Reson., 1979, 36,
56. 6 G. Celebre, G. De Luca, J. W. Emsley, E.
K. Foord, M. Longeri, F. Lucchesini, G. Pileio,
J. Chem. Phys., 2003, accepted for
publication.