The key difference between naphthenes and aromatics is that the naphthenes have only single bonds between carbon atoms whereas the aromatics have both single bonds and double bonds between carbon atoms.
We call naphthenes “cycloalkanes”. These are cyclic aliphatic hydrocarbon compounds. We can obtain them from petroleum. The general formula for these compounds is CnH2n. Moreover, the carbon atoms in these rings are saturated. Aromatics are cyclic hydrocarbons having single bonds (sigma bonds) and double bonds (pi bonds) in an alternating pattern. Therefore, we can observe delocalization of electrons in these compounds, and we call aromatics, “arenes”.
CONTENTS
1. Overview and Key Difference
2. What are Naphthenes
3. What are Aromatics
4. Side by Side Comparison – Naphthenes vs Aromatics in Tabular Form
5. Summary
What are Naphthenes?
Naphthenes are cyclic hydrocarbon compounds having the general formula CnH2n. We can obtain these compounds from petroleum oil via refining. These compounds have one or more saturated ring structures. This means, all the carbon atoms in the ring structures are bonded to each other via only single bonds (no double bonds or triple bonds present). Therefore, these are essentially alkanes. Hence, we call them “cycloalkanes”. The atoms that are present other than carbon are hydrogen atoms. But these hydrogen atoms do not form the ring; they remain attached to the carbon atoms in the ring. According to the number of carbon atoms in these structures, we can name them as cyclopropane, cyclobutane, cyclopentane, cyclohexane, etc.
Figure 01: Cyclobutane
However, there should be at least three carbon atoms to form a cycle, hence the smallest member of these naphthenes is cyclopropane. We call the large cycloalkanes, having more than 20 carbon atoms as “cycloparaffins”. Since the ring area allows these molecules to contact more with each other, the intermolecular attraction forces (London forces) between them are very strong. Hence, the boiling points, melting points, densities of these molecules are higher than that of non-cyclic alkanes having the same number of carbon atoms. Simple and large naphthenes are very stable. Small naphthenes have low stability (due to ring strain). Thus, they are reactive. They can undergo nucleophilic aliphatic substitution reactions.
What are Aromatics?
Aromatics are cyclic hydrocarbon compounds which are consist of conjugated planar ring system with delocalized pi electron clouds. In other words, these structures have an alternating pattern of single bonds and double bonds between the carbon atoms which creates the ring structure. There are no discrete single bonds or double bonds. We call them “arenes”. The name aromatic comes due to the sweet aroma of these compounds.
Figure 02: Some Aromatics
Aromatics can be either monocyclic or polycyclic. Some other compounds which we call “heteroarenes” are also categorized as aromatics. These compounds have atoms other than carbon which forms the ring. But they are aromatics because they form a conjugated pi system and a delocalized electron cloud as well.
What is the Difference Between Naphthenes and Aromatics?
Naphthenes are cyclic hydrocarbon compounds having the general formula CnH2n. These molecules have only carbon atoms which make up the ring. In addition, they have only single bonds between the carbon atoms of the ring. Aromatics are cyclic hydrocarbon compounds that consist of conjugated planar ring system with delocalized pi electron clouds. These molecules may have other atoms such as nitrogen along with the carbon that makes up the ring. Moreover, they have both single bonds and double bonds between carbon atoms in the ring as an alternating pattern. This is the main difference between Naphthenes and Aromatics.
Summary – Naphthenes vs Aromatics
Naphthenes and aromatics are very important hydrocarbon compounds which we can obtain from petroleum oil. The difference between naphthenes and aromatics is that the naphthenes have only single bonds between carbon atoms whereas the aromatics have both single bonds and double bonds between carbon atoms.
Reference:
1. Helmenstine, Anne Marie. “What Are Naphthenes?” ThoughtCo, ThoughtCo. Available here
2. “Aromatic Hydrocarbon.” Wikipedia, Wikimedia Foundation, 27 June 2018. Available here
Image Courtesy:
1.’Cyclobutane-buckled-3D-balls’By Ben Mills – Own work, (Public Domain) via Commons Wikimedia
2.’Aromatic molecules’By Chris Evans, Dr. Roger Peters, Dr. Mike Thompson, Chris Gadsby, Ken Partridge, Roy Mylan, Yehoshua Sivan, Tom Nation, Dr. David Follows, Vikash Hemnath Seeboo (CC0) via Commons Wikimedia