Aromatic hydrocarbons are organic compounds with more than one benzene ring having a strong, pungent smell. Let us study some examples of such aromatic hydrocarbons.
- Benzene
- Ethyl benzene
- Naphthalene
- Phenanthrene
- Toluene
- Phenol
- Hydroquinone
- Nitrobenzene
- Picric acid
- Benzoic acid
- Aniline
- Aspirine
The aromatic hydrocarbon is made up of hydrogen and carbon, forming a ring-like structure. All the types of this particular hydrocarbon have a distinct odor or, say, aroma, so the name is an aromatic hydrocarbon. In this post, let us explain some physical properties of above mentioned aromatic hydrocarbons.
Benzene
Benzene is the best example among the family of hydrocarbons most commonly found in crude oil. It is colorless, and its physical state is liquid. The melting point of benzene is 5.5°C, and the boiling point is 80.1°C. The density of benzene is 0.87gm/m3, which is much lighter than water. It is highly inflammable.
Ethyl benzene
Ethylbenzene is a monocyclic aromatic hydrocarbon with an odor similar to gasoline. The density of ethylbenzene is lighter than water, and its vapor is heavier than the air. The melting point is -95°C, and the boiling point is 136°C.
Naphthalene
Naphthalene is a white crystalline aromatic hydrocarbon which sometimes found in brownish transparent color. It is insoluble in water, and its density is greater than water. The value of density at 15°C is 1.145g/cm3. The boiling point of naphthalene is 217.97°C and its melting point is 78.2°C.
Phenanthrene
Phenanthrene is a polycyclic aromatic hydrocarbon where three benzene rings are fused together. It is a colorless crystalline solid but sometimes appears yellow. The melting point of phenanthrene is 101°C, and the boiling point is 332°C. The density is 1.18g/cm3.
Toluene
Toluene, also called methylbenzene, is a colorless toxic liquid aromatic hydrocarbon with an odor similar to paint thinner. It is insoluble in water. The melting point of -95°C, and a boiling point is 111°C. Toluene is most used as an octane booster in gasoline for the internal combustion engine and also as jet fuel.
Phenol
Phenol is a volatile white crystalline aromatic hydrocarbon that is soluble in water. The melting point of phenol is 40.5°C, and the boiling point is 181.7°C. It has a sweet and tarry odor, and its density is 1.07g/cm3.
Hydroquinone
Hydroquinone, also known as benzene-1,4-diol, is a type of aromatic hydrocarbon that belongs to the phenol group. It is white with a solid density of 1.3g/cm3. The melting point of hydroquinone is 172°C, and the boiling point is 287°C.
Nitrobenzene
Nitrobenzene is a pale yellow oil with an odor similar to almond. It freezes to give a greenish-yellow crystal. Nitrobenzene is insoluble in water, and its density is 1.199g/cm3. The melting and boiling point of nitrobenzene is 5.7°C and 210.9°C, respectively.
Picric acid
Picric acid, also known as 2,4,6 trinitrophenol(TNP), is colorless to yellow solid with a bitter taste. It is highly explosive and has a wide range of applications in the field of health and dye industry. Its density is 1.736g/cm3. The melting point and boiling point of picric acid are 122.5°C and >300°C.
Benzoic acid
Benzoic acid is a white or colorless crystalline solid. It is the simplest aromatic carboxylic acid with a faint and pleasant odor. The density of benzoic acid at 15°C is 1.2659g/cm3 and at 130°C its density is 1.074g/cm3. The melting and boiling point of benzoic acid is 122°C and 250°C, respectively.
Aniline
Aniline is an aromatic hydrocarbon that belongs to the phenol group attached to an amino group. It is a toxic, colorless liquid with a fishy odor. On heavy exposure to air, aniline darkens and turns brown. It is moderately soluble in water. The melting point of aniline is -6.30°C, and the boiling point is 184.13°C.
Aspirine
Aspirin, also called acetylsalicylic acid, is an anti-inflammatory compound that reduces pain and fever. It is a white crystalline solid whose melting point is 136°C, and boiling point is 140°C. Aspirin is readily soluble in water.
Aromatic hydrocarbon structure
Aromatic hydrocarbons are more commonly seen in petroleum and coal. Let us know the structure of the aromatic hydrocarbon.
Aromatic hydrocarbons are in a circular structure. It consists of a carbon atom linked by six equivalent σ bonds and delocalized π bonds. The π electrons share a bond by donating a carbon atom forming a ring. The delocalized π electrons are stable and have a double bond. Thus the ring has an alternative double bond.
Types of aromatic hydrocarbon
The parent of aromatic hydrocarbons is benzene, based on which aromatic hydrocarbons are classified. Let us study the types of aromatic hydrocarbons.
Aromatic hydrocarbons are classified into mainly two types;
- Mono-cyclic aromatic hydrocarbons –consist of only one benzene ring with the functional group attached to them. Examples: Toluene, ethylbenzene, xylene, etc.
- Polycyclic aromatic hydrocarbons –consisting of more than one or, say, multiple benzene rings, for example, naphthalene, biphenyl, pyrene, etc.
Polycyclic aromatic hydrocarbons are generally found in coal and oil deposits. Naphthalene is the simplest polycyclic hydrocarbon to exist.
Properties of aromatic hydrocarbon
Aromatic hydrocarbons are known for their versatile nature and have a wide range of applications in various fields. Let us list such properties of aromatic hydrocarbon.
- Aromatic hydrocarbons are rich in carbon and hydrogen. Thus they have a yellow sooty flame.
- Most of the aromatic hydrocarbons are unsaturated.
- Aromatic hydrocarbons are non-polar molecules. Most of them are insoluble in water.
- Aromatic hydrocarbons undergo both electrophilic and nucleophilic substitution reactions.
- Aromatic hydrocarbons are the most stable compound with a distinct aroma.
- Aromatic hydrocarbons are unreactive in water and cannot form ions or hydrogen bonds with water molecules.
Conclusion
Let us wrap up this post by stating that aromatic hydrocarbons are not entirely related to their smell, but the odor is just a criterion for naming them as an aromatic compounds. Aromatic hydrocarbons are also known as arenes. They are planar compounds resembling benzene in electronic configuration.
Read more about Liquid Hydrocarbon Examples.
Also Read:
- Is carbon malleable
- Carbon density
- Aliphatic hydrocarbon examples
- Liquid hydrocarbon examples
- Saturated hydrocarbon examples 2
- Hydrocarbon examples
- Halogenated hydrocarbon examples
I am Keerthi K Murthy, I have completed post graduation in Physics, with the specialization in the field of solid state physics. I have always consider physics as a fundamental subject which is connected to our daily life. Being a science student I enjoy exploring new things in physics. As a writer my goal is to reach the readers with the simplified manner through my articles.