Restricted Rotation in 9-Phenyl-anthracenes: A Prediction Fulfilled

Abstract

The calculated phenyl rotation barrier in 9-phenylanthracene has been reported as ~21 kcal mol(-1), but experimental verification of this barrier is limited by its intrinsic symmetry. V-T NMR indicated the barrier to interconversion of the syn (C(2v)) and anti (C(2h)) rotamers of 9,10-bis(3-fluorophenyl)anthracene to be ~21 kcal mol(-1). Likewise, the V-T NMR spectra of 9-(1-naphthyl)-10-phenylanthracene reveal that the rotational barrier of the unsubstituted phenyl ring is at least 21 kcal mol(-1).

Tris(tetraceno)triquinacenes: Synthesis and Photophysical Properties of Threefold Linearly Extended Tribenzotriquinacenes

“…The fusion of the planar 5,12‐diphenyltetracene units to the bowl‐shaped triquinacene core in 10 is particularly noteworthy in view of restricted internal rotation. Recently, the barrier towards rotation about the C aryl C aryl bonds in various 9,10‐arylanthracenes was determined to be ≥21 kcal mol −1 32. Actually, the 1 H NMR spectrum of 10 exhibits two distinct doublet resonances for the ortho protons of the six phenyl groups, which remain separated even at 100 °C (see the Supporting Information).…”

“…21 kcal mol À1 . [32] Actually, the 1 H NMR spectrum of 10 exhibits two distinct doublet resonances for the ortho protons of the six phenyl groups, which remain separated even at 100 8C (see the Supporting Information). The 13 C NMR spectrum of 10 also indicates apparently static phenyl groups.…”

Different Rearrangement Behaviour of the Cation or Anion Derived from the Diels–Alder Adduct of 9‐Ferrocenylanthracene and 1,4‐Benzoquinone: Ring‐Opening or Paddlewheel Formation

“…In continuation of our work on restricted molecular rotation in systems combining organometallic sandwich and triptycene moieties, [4][5][6][7][8][9] herein we describe synthetic approaches to novel 9-ferrocenyltriptycenes incorporating an unsymmetrical paddlewheel moiety, for example, 3 b and 3 c. Recently, we reported the addition of benzyne to 9-ferrocenylanthracene (2), and 9,10-diferrocenylanthracene to yield the corresponding symmetrical triptycene paddlewheels that exhibit kinetically slow interconversion of energetically degenerate diastereomers arising from rotation about the three-fold axis of the triptycene. [10] One might envisage that in unsymmetrical ferrocenyltriptycenes (3 c), similar restricted rotation of the ferrocene would give rise to energetically non-degenerate rotational conformations that could function as molecular switches.…”

Symmetry Breaking in NMR Spectroscopy: The Elucidation of Hidden Molecular Rearrangement Processes

“…Initially, 9,10-bis(3-chlorophenyl)anthracene, 21, and 9,10-bis(3-fluorophenyl)anthracene, 22, were synthesized and their variable-temperature NMR spectra were acquired. In the chlorophenyl case, 21, the phenyl ring carbons exhibited multiple 13 C resonances indicating clearly the presence of syn (C 2v ) and anti (C 2h ) rotamers; the barrier to their interconversion was found to be 21 kcal·mol −1 [45]. Moreover, in 22, not only can one see two CF environments in the fluorine NMR spectrum in solution, but also the X-ray crystal structure revealed the presence of equal quantities of syn and anti isomers; the structure of anti-22 appears as Figure 10, and reveals that the fluorophenyls adopt an angle of 85° with the plane of the anthracene thus deviating only slightly from the perpendicular orientation.…”