Aromatic functional groups

Aromatic halides, in which the halogen is attached to the ring, may be prepared by direct electrophilic aromatic substitution or from arylamines via diazonium compounds (see below). 

Benzyl halides may be prepared by the free radical halogenationof the corresponding hydrocarbon using reagents such as A -chloro- or N-bromosuccinimide in the presence of light or a radical initiator. Other methods involve the substitution of benzyl alcohols. Benzyl chlorides may also be prepared by the chloromethylationof aromatic compounds. 

An aromatic ring has a significant effect on the reactivity of the carbon-halogen bond. There are two very different systems aryl halides, exemplified by chlorobenzene, and benzyl halides, exemplified by benzyl chloride. These illustrate the different effects that the presence of an aromatic ring can have on the reactivity of a functional group. 

An aryl halide such as chlorobenzene is relatively unreactive towards nucleophilic substitution. The S l and Sj. 2 pathways involve mechanisms that are not open to aryl halides. The greater s character of the sp bond makes it more difficult to cleave the bond to generate a carbo-cation. However, these restrictions do not apply to radical or carbanion chemistry. Hence, aryl halides undergo radical coupling reactions and metal insertion reactions, leading to organometallic compounds. 

Chloromethylation and the Friedel-Crafts alkylation and acylation take place normally at the ortho and para positions. The insecticide DDT (43, dichlorodiphenyltrichloroethane) is prepared from chlorobenzene and chloral (trichloroethanal). 

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Figure 5.4 Shielding/deshielding Zones for Common Non-aromatic Functional Groups...

Aromatic functional groups (benzene, naphthalene, pyridine rings) ... 

The XAD-8 resin separation of hydrophobic and hydrophilic components of WSOM was also employed by Sannigrahi et al. (2006). The 13C-NMR results indicated that WSOM in urban atmospheric particles is mostly aliphatic in nature (-95% C mass) with major contributions from alkyl and oxygenated alkyls (-80%), carboxylic acid (-10%), and aromatic functional groups (-4%). The authors also found that urban aerosol WSOC are only qualitatively similar to aqueous humic material in terms of functional group distribution. 

Quantitative FTIR data were combined with chemical and petrographic data for the 24 vitrinite concentrates and subjected to bivariate and multivariate statistical analyses in order to identify the effects of coal ification on the aliphatic and aromatic functional groups. 

An aromatic functional group is one in which an aromatic ring is directly attached to the functional group ... 

Copy this revision chart showing the relationship of aromatic dia-zonium compounds to other aromatic functional groups, and fill in the relevant reagents and conditions for the inter-relationships beside the arrows. 

This is the second volume in The Chemistry of Functional Groups series that deals with an aromatic functional group, following on from The Chemistry of Phenols published in 1993. 

Asphaltite exhibits several vibrational absorption bands mostly due to aliphatic and aromatic functional groups. The spectral range investigated here is 3700-1900cm . In such a range, the most prominent bands are those due to the aliphatic and aromatic C-H stretchings. 

FIGURE 16.6 Equations 1 to 5. Reactions of singlet oxygen with vinylic, dienic and aromatic functional groups. 

The most intense and the most useful fluorescence is found m compounds containing aromatic functional groups with low-energy rr - - iransition.s. Compounds containing aliphatic and alicyclic carbonyl structures or highly conjugated double-bond structures... 

An important prerequisite for light-induced degradation is that the plastic absorb solar UVR or visible radiation as only the absorbed light can degrade the plastic. Polyolefins in theory do not have chromophores that can absorb light effectively, but trace impurities in the plastic and some of the additives in the material act as good chromophores. Plastics such as PS, polycarbonate (PC), and polyethylene terephthalate (PET), have aromatic functional groups that absorb UV radiation. 

In addition to reduction, diazonium salts can be converted directly to various other useful aromatic functional groups. Predict the product formed when the diazonium salt 23 is treated with the following reagents ... 

The following sections describe the applications of substituted 1,1-diphenylethylene chemistry for the preparation of phenol, amino, and carboxyl functionalized polymers as well as for the preparation of polymers with aromatic functional groups which provide fluorescent labels. These examples show that anionic functionalization chemistry utilizing substituted 1,1-diphenylethy-lenes as outlined herein provides a versatile and general functionalization methodology for quantitative introduction of functional groups at the chain ends and within the polymer chain by design. 

Two important aromatic functional groups are the phenyl and benzyl groups. A phenyl group is obtained when one of the six equivalent H atoms of a benzene molecule is removed. A benzyl group is obtained by replacing one of the H atoms in a methyl group with a phenyl group. 

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