Quinoline

Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colourless hygroscopic liquid with a strong odor. It is also called 1-azanaphthalene or phenazopyridine.

 Quinoline was first extracted from coal tar in 1834 by German chemist Friedlieb Ferdinand Rung; he called quinoline leukol ("white oil" in Greek). Coal tar remains the principal source of commercial quinoline. In 1842, French chemist Charles Gerhardt Obtained a compound by dry distilling quinine., strychnine, or chinchonine with potassium hydroxide; he called the compound Chinoilin or Chinolein. Runge's and Gephardt's compounds seemd to be distinct isomers beacuse they reacted differently. However, the German chemist August Hoffmann eventually recognized that the differences in behaviors were due to the presence of contaminants and that the two compounds were actually identical. Like other nitrogen heterocyclic compounds, such as pyridine derivatives, quinoline is often reported as an enviromental contaminant associated with facilities processing oil shale or coal, and has also been found at legacy wood treatment sites. Owing to its relatively high solubility in water quinoline has significant potential for mobility in the enviroment, which may promote water contamination. Quinoline is readily degradable by certain microorganism, such as Rhodococcus species Strain Q1, which was isolated from soil and paper mill sludge. Quinolines are present in small amounts in crude oil within the virgin diesel fraction. It can be removed by the process called hydrodenitrification. Quinoline is only slightly soluble in cold water but dissolves readily in hot water and  most organic solvents. Quinoline itself has few applications, ut many of its derivatives are useful in diverse applications. A prominent examole is quinine, an alkaloid found in plants. 4-Hydroxy-2-alkylquinolines (HAQs) are involved in antibiotic resistance.

Structure of Quinoline:

The IUPAC name of quinoline is phenazopyridine, which is being the b-face benzo-fused isomer. The atoms are numbered as shown below structure. The numbering beings from the Nitrogen atom and going counterclockwise around the two condensed rings. The structure of quinoline is shown as follow.

All the ring atoms in Quinoline are sp2 hybridized. The sp2 orbitals of all carbon and nitrogen atom overlap with each other and also with the s orbitals of hydrogen from C-C, C-N, and C-H π bonds. Each ring atom also possesses a P-orbital. These p-orbitals are perpendicular to the plane of the ring. Lateral overlap of these P-orbitals produce a π molecular orbital containing 10 electrons. Quinoline is an aromatic compound since it follows the Huckel's rule (i.e. 4n+2 π electron rule) for n=2. Unlike Indole, the lone pair of nitrogen of quinoline does not participate in the delocalization. Quinoline is a resonance hybrid of several canonical forms as shown below.