Calculations of Molecular Formulae

It may be challenging to memorise if you do not understand hydrocarbons well. However, once you know the subject well, you will find it fascinating! We’ll attempt to make this content as engaging as possible for you in this chapter! Let’s have a look at some of the properties of aromatic hydrocarbons.

Aromatic compounds are called based on the amount and type of ring substitutions. Aromatic hydrocarbons are cyclic hydrocarbons containing delocalised pi electrons between the ring’s carbon atoms. Aromaticity refers to the phenomenon’s aromatic quality. The most basic aromatic chemical is benzene. 

Their powerful, pungent fragrances have made them popular and well-known.

Properties of Aromatic Hydrocarbons

• Aromatic hydrocarbons have a variety of properties, including the fact that their primary sources are petroleum and coal. They’re well-known for their outstanding physical and chemical characteristics. Aromatic compounds with more than one benzene are known as poly-aromatic hydrocarbons. When combined with pollutants in the atmosphere, it is carcinogenic.

• Amino acids and nucleotide precursors are examples of aromatic chemicals. Non-polar hydrocarbons are hydrocarbons that are soluble in water. Unlike water molecules, these hydrocarbons cannot form ions or H-bonds. They are generally unreactive due to their increased stability, and they are regularly utilised as an inert solvent in many chemical and inorganic reactions.

• The carbon-hydrogen ratio has increased. Due to the obvious high carbon content, they are born with such a sooty yellow flame.

• They go through electrophilic and nucleophilic aromatic substitution processes.

• Alkenes and alkynes were unsaturated hydrocarbons with numerous bonds in nature. Because of the unsaturation, they tend to generate additional reactions.

• Aromatic hydrocarbons are stable due to resonance with typical electrophilic substitution processes. In these reactions, each carbon ring works as a nucleophile, while an electrophile assault on benzene is used to generate a substituted product.

• With the introduction of an electrophile, one of the H-atoms in a ring is replaced, resulting in a product that is both stable and aromatic in nature. Aromatic compounds, on the other hand, may lose their aromaticity in addition to reactions, therefore they do not tend to give these reactions.

Uses of Aromatic Hydrocarbons

• Aromatic hydrocarbons are used in a variety of industries. Toluene is often used as a solvent in model glues, whereas naphthalene is utilised as a mothball.

• Phenanthrene is an intermediate chemical used in the production of colours, explosives, and pharmaceuticals which has a separate synthesis method. Trinitrotoluene (TNT), also known as 2, 4, 6 trinitrotoluena, is a common aromatic chemical used in explosives and explosive manufacture.

• Catechol, also known as 1, 2 benzenediols or pyrocatechol, is among the most significant components of a photographic developer.

Reactions of Aromatic Compounds

Aromatic compounds can take part in a variety of processes, such as substitution, coupling, as well as hydrogenation.

The benzene ring is well-known for the stability it achieves as a result of its aromaticity. Aromatic compounds, on the other hand, can take place in a variety of chemical processes, like substitution, coupling, as well as hydrogenation. The reactivity is attributed to electrons within the benzene ring’s pi system. Whereas a continuous electron density distributed equally around in the aromatic core is the ideal representation for aromatic compounds, the alternating single and double bonds which are usually shown are particularly effective when forecasting the reactivity of aromatic compounds.

Many of the processes that occur in alkenes (carbon-carbon double bonds) also occur in aromatic compounds, however, the activation barrier is often higher to a stabilising influence of aromaticity (ca. 36 kcal/mol).

Aromatic Compounds with a Single Substituent

The substituent is introduced as a prefix to benzene whenever the benzene ring contains just one substituent and the substituent has six or fewer carbons. The alkyl groups are known by their alkane sequence, which ends in -yl: methyl (one carbon), ethyl (two carbons), propyl (three carbons), etc.

If the substituent has much more than six carbons, the alkane component is termed first, followed by the aromatic ring portion as a suffix. An aromatic ring attached to an 8-carbon chain, for example, would be 1-phenylacetate, not octylbenzene.

Aromatic Compounds with Multiple Substituents

When there are a lot of substituents, ring atoms are identified to reduce the numbers assigned to the substituted positions.

The prefix ortho– is being used unless the substituents are already on opposite sides of the ring (1,2), meta– is used if they are separated by one ring position (1,3), and para– is used if they are on opposite ends of the ring (1,4).

Polycyclic Aromatic Hydrocarbons

• Polycyclic aromatic hydrocarbons are made up of fused aromatic rings. Coal, tar, oil, as well as some prepared items like smoked salmon, burnt toast, and so on contain them.

• Naphthalene is a common example of these polycyclic hydrocarbons. Pollutants are stated to be present in these substances.

• Methylbenzene, Naphthalene, Phenanthrene, Trinitrotoluene, and o-dihydroxybenzene are examples of aromatic hydrocarbons.

Conclusion

In this topic we learned that physical features plus chemical reactivity could be used to identify and distinguish hydrocarbons. Although aromatic compounds are usually stable, they are unreactive and can only be reacted with the help of a catalyst.