Aromatic Hydrocarbons - Fundamentals
Introduction to Aromatic Hydrocarbons
Hydrocarbons are categorized into open-chain and closed-chain hydrocarbons. In the closed-chain hydrocarbons, there is another sub-divison of homonuclear and heteronuclear hydrocarbons. An aromatic hydrocarbon is a closed-chain hydrocarbon consiting of carbon atoms linked together in forming a closed ring-like structure. In the early days, aromatic hydrocarbons were characterized by their sweet smell - termed as aroma. An aromatic hydrocarbon can be homonuclear or heteronuclear both.
In modern days, aromatic hydrocarbons are also defined as benzene and derivatives of benzene. Examples are: Benzene, Pyridine, Napthalene, etc.
Figure given alongside is of Benzene (C6H6). The empirical formula of Benzene is (CH).
Characteristics of Aromatic Hydrocarbons
Following are the characteristics of aromatic hydrocarbons:
- They have closed ring-like structure and a conjugated system.
- As discussed in the introduction section, they are closed-chain hydrocarbons. Also, they have a conjugated system. It means that there exists alternate double bond or delocalized pi-electrons in the system of carbon atoms.
- They have high resistance towards addition reaction.
- No compound in nature would like to loose its property after getting invovled in a chemical reaction. If an aromatic hydrocarbon gets involved in addition reaction, it looses its aromaticity.
- They are highly unsaturated hydrocarbons. They contain multiple double bonds in their carbon structure.
- Aromatic hydrocarbons produce a dark and sooty flame when burnt completely.
- These compounds exhibit electrophilic substitution reaction.
Following are the criteria:
- The carbon structure should be cyclic and planar. All the carbon atoms should lie on the same plane.
- It should have a conjugated system.
- It should follow Huckel's rule of Aromaticity (4n+2) pi electrons where n = 0,1,2,3,... .
- Rules for Aromaticity: The 4 Key Factors – Master Organic Chemistry
- Benzene-2D-flat.png (958×1100) (wikimedia.org)
