PROPERTIES OF AROMATIC COMPOUNDS

Aromatic hydrocarbons are nonpolar, and are insoluble in water. They commonly undergo reactions like aromatic electrophilic substitution reactions and reduction reactions. 

Aromaticity of compounds is based on certain rules. According to Huckel s rule, the number of pi electrons present should be a number denoted by the formula 4n + 2, where n is 0,1,2,3, Hence, for compounds to be consid- 

Test whether you can recognize the aromaticity of the structures in the examples that follow  

Step 2 - See whether there is a cyclic p orbital overlap. 

Number of pi electrons — 6 Cyclic overlap ofp orbitals - Yes Aromatic - Yes 

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We 11 examine the chemical properties of aromatic compounds from two different perspectives... 

While benzene was the first aromatic system studied, the formulation of HtickePs rule and the theory behind it created an impetus to prepare non-benzenoid species such as the tropylium cation and cyclopentadienyl anion that also obeyed Huckel s rule to see if these species were also aromatic. This required that the properties of aromatic compounds be defined. 

In his first published paper on the structure of benzene in 1922, Ingold stated his aim to unify aliphatic and aromatic chemistry by studies of ring formation of unsaturated systems. He argued that chemists must accept the Dewar formulation, using a bridged phase of benzene, in order to relate the properties of aromatic compounds to the facts of aliphatic chemistry. 31... 

The special properties of aromatic compounds and conjugated systems are related to the regular alternation of single and second-order C-C bonds along molecular chains. Each second order bond is associated with a balanced charge circulation and a couple of odd electrons with paired spins. The... 

Predict the properties of aromatic compounds and the effects that aromatic rings have on neighboring parts of the molecule. 

All previous examples referred to the anomalies due to out-of-plane distortions of the aromatic rings. Properties of aromatic compounds could also be affected by in-plane angle distortions caused by a fusion of a small ring and an aromatic residue. Among various compounds which have been designed and synthesized for investigations into these effects, the most interesting data were obtained for tris(benzocyclobutadieno)benzene 197, easily prepared by the... 

An empirical steric index, denoted as 2D, for substituted benzene rings and defined as the 6-term sum of the distances, given by the L Sterimol length parameter, between the six atoms bonded to the benzene carbon atoms, i.e. the value of the external perimeter of the benzene ring [Taillander et ai, 1983 Ravanel et al., 1985]. It represents the perimeter of the efficacious section and describes the steric properties of aromatic compounds. 

J. Malkin, Photochemical and Photophysical Properties of Aromatic Compounds, CRC Press, Boca Raton, 1992, pp. 117, 201. 

Aromatic compounds have not only been of academic interest ever since organic chemistry became a scientific discipline in the first half of the nineteenth century but they are also important products in numerous hydrocarbon technologies, e.g. the catalytic hydrocracking of petroleum to produce gasoline, pyrolytic processes used in the formation of lower olefins and soot or the carbonization of coal in coke production [1]. The structures of benzene and polycyclic aromatic hydrocarbons (PAHs) can be found in many industrial products such as polymers [2], specialized dyes and luminescence materials [3], liquid crystals and other mesogenic materials [4]. Furthermore, the intrinsic (electronic) properties of aromatic compounds promoted their use in the design of organic conductors [5], solar cells [6],photo- and electroluminescent devices [3,7], optically active polymers [8], non-linear optical (NLO) materials [9], and in many other fields of research. 

Solution In order to answer this question, a knowledge of the properties of aromatic compounds is necessary. 

We have dealt with the theoretical side of aromaticity, but what does it mean in practice What peculiar properties of aromatic compounds do porphyrins partake of that allow them to do what they do Once again, we shall consider benzene as the model aromatic compound and then see how its properties appear, modified, in porphyrins. 

Magnetic Properties of Aromatic Compounds and Aromatic Transition States... 

If the transition state of the Diels-Alder reaction is indeed aromatic, it should exhibit the typical magnetic properties of aromatic compounds, such as anomalous NMR shifts, and diamagnetic susceptibility anisotropy and exaltation. Unfortunately, properties of transition states are difficult to measure. However, NMR... 

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