Aromaticity planar

Covalent compounds, arising from the attack of strong oxidizing systems, such as fluorine or Mn(VII), on graphite. The aromatic planarity of the graphite sheet is destroyed, and a buckled, sp -hybridized sheet is created. 

Scheme 3.2-44. From two-dimensional n aromatics (planar 2, C2BH3) to three-dimensional o aromatics (polyhedral 15, 39 and higher members of the series) via folded aromatics (3, 2 ) connecting both classes.

Naturally, the concept of intramolecular coordination in hthium chemistry via side-arm complexation is not limited to aromatic planar aryls. Like the metalation of cyclohexane... 

The above models are representative of the active macerals, particularly vitrinite. Inert macerals, such as fusinite and micrinite, are believed to have large aromatic planar structures with fewer substituents (14) and behave similar to chars. 

At this point, we notice that the corannulene molecule provides an ideal model for addressing a very interesting problem how much aromaticity is lost when a molecule is distorted from the strongly aromatic planar structure to a nonplanar structure The answer to this question must be a key to the possible existence of superaromaticity in the C60 molecule (5). 

CS2P4-2NH3 Xray PNMR (P4 ) aromatic planar anion... 

Benzene is described by molecular orbital theory as a planar, cyclic, con jugatea molecule with six tt electrons. According to the Hiickel rule, a molecule must have 4m 2 7T electrons, where n = 0, 1, 2, 3, and so on, to be aromatic. Planar, cyclic, conjugated molecules with other numbers of tt electrons are antiaromatic. 

These compounds satisfy the criteria for aromaticity (planar, cyclic n system, and the Huckel number of 4n -I- 2 71 electrons) pyrrole, imidazole, indole, pyridine, 2-methylpyridine, pyrimidine, and purine. The systems with 6 7i electrons are pyrrole, imidazole, pyridine, 2-methylpyridine, and pyrimidine. The systems with 10 7i electrons are indole and purine. The other nitrogen heterocycles shown are not aromatic because they do not have cyclic 7i systems. 

Alkoxyazocines exist in tub conformation without conjugative stabilization, but its dianions, obtained by electrochemical or chemical reduction, exist in aromatic planar conformation <71JA16l, 71JA168>. The existence of 3,8-dimethyl-2-methoxyazocine (DMMA) dianion radical (20) along with its electron distribution and thermodynamic stability were reported for the first time in 1983 <83JA6078>. Reduction of DMMA in HMPA with metal sodium or potassium yielded an anion... 

Thermotropic polyester backbone chemistry is characterized by a high degree of aromaticity, planarity, and linearity in the chain backbone. Most common moieties are p-phenylene, 1,4-biphenyl, and 2,6-naphthalyl moieties linked by ester or amide linkages. Polymers that form liquid crystal phases in the melt are thermotropic, whereas those that form liquid crystalline phases in solution are lyotropic. The all-aromatic polyester homopolymers tend to be intractable, decomposing at temperatures well below their melting points and insoluble in most... 

Alonso et al. (2011PCCP20564) have successfully applied the neural network methodology in the study of the substituent effect on aromaticity for a set of pyrimidine derivatives with a potential push-pull character. The interplay between aromaticity, planarity, steric effect, and charge transfer properties of all substituted pyrimidine derivatives has been also discussed (2011PCCP20564). 

Aromatic ions (Section 14.7D) Cations and anions that fulfill the criteria for aromaticity (planarity, electron delocalization, and a Hiickel number of TT-electrons) and thus have additional (aromatic) stability. 

Consider the set of perpendicular -orbitals in the poly aromatic planar molecule coronene shown below. This set gives rise to a symmetry of molecular orbitals of a u and b g. Can you draw both these orbitals (Use the standard orientation of the central benzene frame, as shown in Fig. 3.10)... 

In 1992, de Mendoza" and his group reported the synthesis of a receptor for amino acids, 43, in zwitterionic form featuring a guanidinium function to bind carboxy-late, and a crown ether to recognize ammonium unit. An aromatic planar surface, the naphthalene ring, for an... 

Spectroscopic studies of conductive oligomers have been carried out mostly in solution except for a few examples [167], In solution, especially at low concentrations of the oligomers, individual molecules are widely separated and so interaction between them is likely to be weak. It is well-known, however, that once charges are introduced into an aromatic planar molecule in an appropriate way such charged species easily form molecular associates such as dimer radical cations as a consequence of interaction with the neutral molecule(s) in the vicinity. This can be observed even in relatively dilute solution or in organic glasses in which the... 

---