Question

What are the main classifications of hydrocarbons? What are their generic molecular formulas?

Short answer

Hydrocarbons are classified as Saturated (Alkanes: \( C_nH_{2n+2} \)), Unsaturated (Alkenes: \( C_nH_{2n} \), Alkynes: \( C_nH_{2n-2} \)), and Aromatic, with alkanes having single bonds, alkenes and alkynes having double and triple bonds, and aromatic hydrocarbons containing benzene rings or variations thereof.

Step-by-step solution

Identify the Main Classifications of Hydrocarbons

The main classifications of hydrocarbons are based on the type of bonds between carbon atoms and the structure of the carbon chain. There are two major categories based on types of bonds: Saturated hydrocarbons and Unsaturated hydrocarbons. Saturated hydrocarbons have single bonds only and are also known as alkanes. Unsaturated hydrocarbons have one or more double or triple bonds and include alkenes (with double bonds) and alkynes (with triple bonds). Hydrocarbons can also be classified based on the structure of the carbon chain into aliphatic (which includes alkanes, alkenes, and alkynes) and aromatic hydrocarbons.

Determine the Generic Molecular Formulas

Each classification of hydrocarbons has a generic molecular formula: Alkanes have the formula \( C_nH_{2n+2} \), where \( n \) is the number of carbon atoms. Alkenes have the general formula \( C_nH_{2n} \), and alkynes have the general formula \( C_nH_{2n-2} \). Aromatic hydrocarbons, on the other hand, usually contain at least one benzene ring \( C_6H_6 \), but their structures can be more complex and the formulas vary more than those of aliphatic hydrocarbons.

Key concepts

Saturated Hydrocarbons

Saturated hydrocarbons consist exclusively of single bonds between the carbon atoms within their molecular structure. These compounds are the simplest form of hydrocarbons and are also commonly referred to as alkanes. Due to their single bonds, they are generally less reactive than unsaturated hydrocarbons, making them relatively stable compounds. A significant characteristic of saturated hydrocarbons is their systematic generic molecular formula, which is expressed as \( C_nH_{2n+2} \), where \( n \) denotes the number of carbon atoms. For instance, methane (\( CH_4 \)), ethane (\( C_2H_6 \)), and propane (\( C_3H_8 \)) are all examples of saturated hydrocarbons.

These hydrocarbons tend to have higher melting and boiling points when compared to their unsaturated counterparts of similar molecular weight. They are found in many common fuels such as propane gas, natural gas, and petrol.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons are molecules that contain at least one double or triple bond between carbon atoms. These double or triple bonds introduce kinks in the hydrocarbon chain, making these molecules more chemically active than their saturated counterparts. Unsaturated hydrocarbons are broadly divided into two categories: alkenes, with at least one double bond, having the generic molecular formula \( C_nH_{2n} \); and alkynes, with at least one triple bond, represented by the formula \( C_nH_{2n-2} \).

Ethene (\( C_2H_4 \)), with a double bond, and acetylene (\( C_2H_2 \)), with a triple bond, serve as the simplest examples of alkenes and alkynes, respectively. These hydrocarbons play a crucial role in the chemical industry, serving as fundamental building blocks for polymers and numerous other chemical compounds.

Generic Molecular Formulas

The generic molecular formulas of hydrocarbons are simple representations that provide insight into the composition of these compounds, indicating the ratio of carbon to hydrogen atoms. Alkanes, alkenes, and alkynes have distinct formulas that help in classifying and understanding the structure of hydrocarbon molecules.

Alkanes follow the formula \( C_nH_{2n+2} \), alkenes adhere to \( C_nH_{2n} \) and alkynes to \( C_nH_{2n-2} \), where \( n \) represents the number of carbons within the compound. These formulas are integral to predicting the properties of hydrocarbons and are a fundamental concept in organic chemistry. With these formulas, one can also deduce potential reactivity and the type of reactions a hydrocarbon may undergo.

Aliphatic and Aromatic Hydrocarbons

Hydrocarbons are also classified based on the overall structure of the carbon chain present in the molecule. Aliphatic hydrocarbons include linear, branched, and cyclic (non-aromatic) structures, encompassing alkanes, alkenes, and alkynes. These can be further segregated as straight-chain, branched-chain, or ring structures that do not contain delocalized electrons. Aromatic hydrocarbons, however, are characterized by the presence of a benzene ring - a hexagonal ring of carbon atoms with alternating double and single bonds.

A classic example of an aromatic hydrocarbon is benzene, \( C_6H_6 \), known for its planar structure and delocalized electrons contributing to its unique chemical stability, a concept referred to as aromaticity. Aromatic compounds have different chemical properties than aliphatic hydrocarbons and are significant in the manufacture of dyes, plastics, pharmaceuticals, and explosives.