Preparation of Benzene: Aromatic Compounds in Organic Chemistry

Ans. The six carbon atoms in benzene are sp² hybridized. The two sp² hybrid orbitals of each carbon atom overlap with the sp² hybrid orbitals of adjacent carbon atoms to form six C–C sigma bonds in the hexagonal plane. The remaining sp² hybrid orbital on each carbon atom overlaps with the s-orbital of hydrogen to form six C - H sigma bonds. Each carbon atom is now left with one unhybridized p orbital. The remaining unhybridized p-orbital of carbon atoms has the possibility of forming three π bonds by the lateral overlap of three π bonds by overlap of p orbitals of C1 –C2, C3 – C4, C5 – C6 or C2 – C3, C4 – C5, C6 – C1 respectively. The six π electrons are thus delocalized and can move freely about the six carbon nuclei. The delocalized π electron cloud is attracted more strongly by the nuclei of the carbon atoms than the electron cloud localized between two carbon atoms. Therefore, the presence of delocalized π electrons in benzene makes it more stable.

Ans. Benzene and polynuclear hydrocarbons consisting of more than two benzene rings combined together are toxic and are said to contain cancer-producing (carcinogenic) properties. Such polynuclear hydrocarbons are formed due to the incomplete combustion of organic materials such as tobacco, coal, and petroleum. They find their way into the human body and go through various biochemical reactions and finally damage DNA and cause cancer. Some of the carcinogenic hydrocarbons are 1,2-Benzanthracene, 3-Methylcholanthrene, 1,2-Benzpyrene, 1,2,5,6-Dibenzanthracene, and 9,10-Dimethyl-1,2-benzanthracene. 

Ans. The characteristic of Benzene are as follows:

• Volatile and flammable nature
• carcinogenic and toxic
• colorless
• characteristic odor

Ans. A compound is considered an aromatic compound if it fulfills the Hückel Rule which states that the compound should have the following characteristics:

• It is planar
• The π electrons in the ring are completely delocalized.
• (4n + 2) π electrons in the ring are present where n is an integer (n= 0, 1, 2, .....)

Ans. The English scientist, Michael Faraday discovered benzene in 1825. However, August Kekulé in 1865 proposed that benzene has a cyclic arrangement of six carbon atoms with alternate single and double bonds and one hydrogen atom attached to each carbon atom.

Ans. The various methods of preparing benzene in the laboratory are as follows:

• Cyclic polymerization of ethyne
• Decarboxylation of benzoic acid
• reduction of phenol
• hydrolysis of sulphonic acid

Ans. Benzene has a wide range of uses. Some of its uses are as follows:

• It is used in the printing industry as many products used by them contain benzene. Some of the products that have benzene are used for cleaning printing equipment to increase the duration of their life cycle.
• Benzene is used in the production of dyes, nylon fibres, medicines, pigments, insecticides, adhesives, soaps and cleansers etc.
• It is used in manufacturing different chemicals such as ethylbenzene, cumene and cyclohexane.

Ans. The polymerisation of ethyne occurs at 873 K.

Ans. Benzene is a non-polar molecule and is colorless with a gasoline-like aroma. It is immiscible with water but is readily miscible with organic solvents. Also, it burns with a sooty flame.

Ans. When vapors of phenol pass over heated zinc dust, phenol reacts with zinc dust to convert to a phenoxide ion and a proton, which accepts an electron from Zn forming an H radical. This results in the formation of ZnO and the phenoxide ion that was formed, converts itself into Benzene.