Dipole Parallel-Alignment in the Crystal Structure of a
Polar Biphenyl: 4'-Acetyl-4-Methoxybiphenyl (AMB)
Rainer Glaser,* Nathan Knotts, Zhengyu Wu, and
Department of Chemistry,
University of Missouri-Columbia,
Columbia, Missouri, 65211 (USA)
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The crystal structure
of (MeO, Acetyl)-biphenyl syn-AMB features
perfect dipole-parallel alignment along the long axis
within 2-dimensional layers and also near-perfect
dipole-parallel alignment in the stacking direction.
In contrast, the crystal structure of
the analogous "(MeO, Acetyl)-phenyl", 4-methoxyacetophenone
(syn-MAP), is not polar.
The MP2(full)/6-31G* optimized structures of
(MeO, Acetyl)-biphenyl AMB
with syn conformation,
(t = 42.9o,
a = -0.3o,
m = 0.3)o
and anti conformation,
(t = 42.9o,
a = -0.5o,
m = 0.0o).
Space-filling models of a 2d-layer viewed down the c direction with
acetyl groups in the foreground, respectively.
Each AMB molecule engages
in two (ff|ee) contacts A
and two (ff|ee) contacts B
as well as two (ff|ff) contacts C
and two (ff|ff) contacts D.
For comparison, the crystal structure of biphenyl itself at room
also contains planar biphenyls with
Figure 5. (in paper only)
The dipole moments of the AMB molecules are additive in the c
Across the layer interface, each AMB molecule engages
in two EN-CH2-H...O contacts with another
AMB molecule. These
interactions are responsible for the syn conformation
and the directionality of the layer stacking in the
Perspectives of the EN-CH2-H...O
that contribute to interlayer bonding;
d(OCH2-H...O=C) = 2.672 Ang. and
d(COCH2-H...O) = 2.715 Ang.