Difference Between Aromatic and Aliphatic

The key difference between aromatic and aliphatic is that aliphatic compounds have straight, branched or cyclic structures whereas aromatic compounds contain a cyclic structure.

Organic molecules are molecules that consist of carbons. They are the most abundant molecules in living things on this planet. Organic chemists divide all the organic compounds into two groups as aliphatic and aromatic compounds. This separation is dependent on the way carbon atoms are arranged in the molecule.

CONTENTS

1. Overview and Key Difference
2. What is Aromatic 
3. What is Aliphatic
4. Side by Side Comparison – Aromatic vs Aliphatic in Tabular Form
5. Summary

What is Aromatic?

Studies about aromatic compounds started with the discovery of a new hydrocarbon by Michael faraday in 1825. This new hydrocarbon compound was named as “bicarburet of hydrogen”. Further studies about this compound showed that it has different characteristics than other organic compounds. The molecular formula of benzene is C₆H₆, and it is surprising because it has the same number of carbon atoms and hydrogen atoms. Most of the initially identified aromatic compounds were resins and essential oils, which had a fragrance. This gave them the name “aromatic.”

Kekule was the first to recognize these aromatic compounds. He also proposed the structure of benzene, which eventually became the parent compound of all the aromatic compounds. Though the formula shows a highly unsaturated nature in benzene, its reactions are contradictory. Normally, unsaturated compounds like alkene decolorize bromine; change the colour of potassium permanganate by being oxidized, etc. However, benzene doesn’t show any of these. So they show different relativities than unsaturated aliphatic compounds.

Aromatic Compounds

By saying a compound is aromatic, we mean that its π electrons are delocalized over the entire ring and that it is stabilized by the π electron delocalization. When naming monosubstituted benzene, we can adopt two methods. In some compounds, we use benzene as the parent name and we can indicate the substituent by a prefix (ex: bromobenzene). In other compounds, the compound takes a new name (ex: toluene).

In addition to simple benzene and benzene derivatives, there are other aromatic compounds. Polycyclic benzenoid aromatic hydrocarbons are one of them. This class has molecules with two or more fused benzene rings (ex: naphthalene). Furthermore, there are nonbenzenoid aromatic compounds like azulene and cyclopentadienyl anion. Other than the rings composed only on carbon atoms, there are some other aromatic molecules which are heterocyclic. Pyridine, furan, and pyrrole are some examples of heterocyclic aromatic compounds.

What is Aliphatic?

Aliphatic compounds in organic chemistry are the non-aromatic compounds. They are either cyclic or acyclic. Alkanes, alkenes, alkynes and their derivatives are the major aliphatic compounds.

These compounds can have branched or linear structures and are either saturated (alkanes) or unsaturated (alkenes and alkynes), which means they may have double bonds between carbon atoms(unsaturated) or no double bonds at all(saturated).

What is the Difference Between Aromatic and Aliphatic?

Aromatic compounds are organic compounds containing a planar unsaturated ring of atoms, which is stabilized by an interaction of the bonds forming the ring while aliphatic compounds are organic compounds whose carbon atoms link with each other in open chains, either straight or branched, rather than containing a benzene ring. Hence, the key difference between aromatic and aliphatic is that aliphatic compounds have straight, branched or cyclic structures whereas aromatic compounds contain a cyclic structure. Moreover, all aromatic compounds have a sweet, pleasant odour, but most aliphatic compounds are odourless.

Summary – Aromatic vs Aliphatic

Both aromatic and aliphatic compounds are organic compounds. The key difference between aromatic and aliphatic is that aliphatic compounds have straight, branched or cyclic structures whereas aromatic compounds contain a cyclic structure.

Reference:

1. Helmenstine, Anne Marie. “Definition of an Aliphatic Compound.” ThoughtCo, Dec. 3, 2018, Available here.

Image Courtesy:

1. “2876288” (CC0) via Pixabay
2. “Butan Lewis” By NEUROtiker ⇌ – Own work (Public Domain) via Commons Wikimedia