Preparation and Properties of Molecules Having High Steric Crowding. 1,8-Diphenylnaphthalenes
<p>The 1,8-diarylnaphthalenes have distinctive properties and geometric features which result from the forced proximity of the adjacent periaryl rings. We have developed an efficient synthetic route to 1,8-diphenylnaphthalene derivatives which involves a direct coupling between the pheny...
| Summary: | <p>The 1,8-diarylnaphthalenes have distinctive properties and
geometric features which result from the forced proximity of the
adjacent periaryl rings. We have developed an efficient synthetic
route to 1,8-diphenylnaphthalene derivatives which involves a direct
coupling between the phenyl and naphthyl rings with an organonickel
catalyst. The magnitude of the strain energy resulting from the
overcrowding in 1,8-diphenylnaphthalene 1 is determined using
combustion calorimetry. An X-ray analysis of peri-diphenyl-
acenaphthene 2 is reported. The over crowded phenyl rings of
2 are face to face and nearly perpendicular to the naphthalene ring
plane. Large structural distortions are found, especially in the
naphthalene framework. A comparison of the geometries of several
1,8-diphenylnaphthalenes having different types of steric interactions
at the 4,5 positions is made, and an analysis of distortions in terms
of induced stress vectors which act throughout the naphthalene
framework is presented. Striking effects in both the proton and C-13
nmr spectra of derivatives of 1 are found which are correlated with
a near-perpendicular solution conformation of the phenyl and naphthyl rings.</p>
<p>The phenyl rings in derivatives of 1 have surprisingly low
barriers to a 180° rotation about the phenyl-naphthyl bond.
Comparison of rotational barrier measurements for analogs and derivatives of 1
including the highly strained 1,4,5,8-tetraphenyl-naphthalene,
together with other observations, indicates that the
transition-state to phenyl-ring rotation involves substantial concurrent
warping of the naphthalene ring as a whole. Substitution in the phenyl-ring
ortho position raises the rotational barrier considerably; cis and tram
rotational isomers of 1,8-di-o-tolylnaphthalene are isolated
and studied.</p>
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