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Rearrangement Reactions in Organic Chemistry

Rearrangement reactions occur when one single reactant undergoes a bond and atom reorganization to yield an isomeric product. As the name suggests, a rearrangement is an intramolecular reaction whose product is an isomer of the starting material. It is often unavoidable to introduce many atoms that will be later discarded; the rearrangement itself is a process offering the best possible atom economy that is all atoms present in the reactant are found in the product.

Photochemical smog is produced from the action of sunlight on the nitrogen oxides and hydrocarbons present in the exhaust gases of the automobiles and factories. Photochemical smog, first identified in Los Angeles in the late 1940s, is nowadays a widespread phenomenon in many major cities of the world. Photochemical smog is due to the formation of free radicals. These are formed as a result of a series of photochemical changes when UV radiation from the sun is absorbed by SO2, oxides of nitrogen and hydrocarbons.

Rearrangement Reaction Examples

The rearrangement reactions can be classified or divided into several categories. For example, the mechanism of the process may be intramolecular or intermolecular. Other classification looks at specific mechanisms of the process. Also, the reactions may be classified according to the type of migration of specific groups.

Some rearrangement reaction may take place at elevated temperatures and others necessarily require the use of a catalyst or the use of a catalyst significantly improves the reaction yield. In some cases, the presence of a catalyst is the most dominant factor for the successful reaction outcome and the formation of energetically favored rearrangement products.

Among many examples of an intermolecular rearrangement, 3,3-sigmatropic rearrangement reaction reaction is an important avenue leading to functionalized amino sugars, Ichikawa et al [3,4] developed practicable synthetic approach to many amino functionalized sugars via the rearrangement of carbohydrate isocyanates.

Photochemical Smog Effects

Ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate are the primary constituents of photochemical smog. Under moist, dry, and sunny environments photochemical smog occurs. The key components of photochemical smog stem from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by cars and factories.

  • Photochemical smog poses significant problems to the skin. Ozone and peroxyl nitrate both act as potent eye irritants.
  • Photochemical smog leads to rubber weeping and substantial plant life damage. It also causes metal, stone, construction materials, rubber and painted surfaces to become corrosive.
  • The nose and throat are irritated by ozone and nitric oxide and their high concentration induces headache, chest pain, throat dryness, cough and trouble breathing.

If we monitor the primary photochemical smog precursors such as NO2 and hydrocarbons, the secondary precursors such as ozone and peroxyl nitrate, the photochemical smog will naturally be reduced. For cars, catalytic converters may typically be used and may avoid the release of nitrogen oxide and hydrocarbons into the atmosphere. Many plants such as pinus, juniperus, quercus, pyrus, and vitis can metabolize nitrogen oxide to help reduce photochemical smog by their plantation.

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