Introduction

Relevance of the Topic

Organic Functions and, specifically, the Nomenclature of Aromatic Hydrocarbons are key elements to unveil the fascinating world of Organic Chemistry. This branch of chemistry has a huge impact on our daily lives and in various industrial areas, from pharmaceuticals, cosmetics to fuels. The concept of functionality is the backbone of organic chemistry, and today's class will focus specifically on aromatic hydrocarbons!

Contextualization

Aromatic Hydrocarbons are within the category of cyclic compounds in Organic Chemistry, which is the basis for the study of a multitude of organic compounds. The benzene ring (the simplest and most common aromatic ring) is a key structure in the constitution of many compounds found in nature and produced synthetically. By understanding its structure and nomenclature, students will be able to take a qualitative leap in the understanding and application of organic chemistry.

Theoretical Development

Components

• Structure of aromatic hydrocarbons: Characterized by the presence of one or more benzene rings, which is a cyclic ring with six carbon atoms, where there is an alternation of single and double bonds. Each carbon in the ring is bonded to a hydrogen atom. The benzene ring can be represented in two ways: one with alternating double bonds and another with a circle in the center of the hexagon representing the delocalization of π electrons.
• Resonance in aromatic hydrocarbons: A chemical phenomenon that explains the chemical behavior of aromatic hydrocarbons, as they are neither exactly aliphatic compounds (with single bonds) nor exactly unsaturated compounds (with double bonds). The benzene ring exhibits exceptional stability due to the delocalization of π electrons, which can be represented by resonant structures.

Key Terms

• Hydrocarbons: Chemical compounds consisting of carbons and hydrogens.
• Aromatic hydrocarbons: Class of hydrocarbons that have benzene rings.
• Benzene Ring: A cyclic ring of six carbons with delocalization of π electrons.
• IUPAC (Prefix, Infix, and Suffix): System used to name aromatic hydrocarbons. The prefix indicates the number of carbons, the infix can indicate the type of chemical bond, and the suffix the organic function.
• Resonance: Refers to electronic delocalization in a molecule where the most stable energy state of the molecule is not represented by a single Lewis structure, but is a combination of structures.

Examples and Cases

• Benzene: Benzene is the simplest aromatic hydrocarbon. It has a molecular formula of C6H6. Its structure is a ring of six carbons, with each carbon forming bonds with one hydrogen and two other carbons. The carbons are bonded to each other through alternating single and double bonds, forming a conjugated system.
• Toluene: Toluene is an aromatic hydrocarbon derived from benzene and has the formula C7H8. The difference is that, instead of one of the hydrogens in the benzene ring, there is a methyl group (-CH3). In nomenclature, toluene can also be named as methylbenzene.
• Naphthalene nomenclature: Naphthalene is an example of a polycyclic aromatic hydrocarbon, meaning it has more than one benzene ring. It has a molecular formula of C10H8 and a structure formed by the fusion of two benzene rings. The nomenclature may vary depending on the position of the substituents on the rings.

Detailed Summary

Key Points

• The relevance of aromatic compounds in our daily lives and industry is vast. They are essential in the production of medicines, plastics, dyes, adhesives, among others.
• Aromatic compounds are hydrocarbons that have one or more unsaturated and planar benzene rings in their structure. These rings, due to the delocalization of π electrons, have exceptional chemical stability.
• IUPAC nomenclature names benzene as the basic aromatic hydrocarbon and all others are considered derivatives of it.
• The IUPAC nomenclature system for these compounds includes a prefix (indicating the number of carbons), an infix (indicating the type of chemical bond present), and a suffix (indicating the organic function).
• Resonance is a phenomenon in which a molecule has more than one valid Lewis structure, as in the case of benzene.

Conclusions

• Understanding the concept of aromatic hydrocarbons is fundamental for the understanding of organic chemistry.
• Benzene is the most basic aromatic hydrocarbon, being the starting point for the nomenclature of other compounds in this class.
• The IUPAC nomenclature system is essential in the correct identification and naming of aromatic hydrocarbons.
• Resonance is a chemical phenomenon that explains the stability of aromatic hydrocarbons; without understanding this concept, the nature of aromatic compounds would not be fully understood.

Suggested Exercises

1. Nomenclature of Aromatic Hydrocarbons - Given the following compounds, name them using the IUPAC nomenclature system: C6H5-CH3; C6H5-CH2-CH3; C6H5-COOH.

2. Structure and Resonance - Draw the Lewis structure of benzene showing the delocalization of π electrons and explain what this means.

3. Identification of Aromatic Compounds - From a provided list of compounds, identify which are aromatic hydrocarbons and justify your answer.