Hydrocarbons

This chapter introduces hydrocarbons, organic compounds made only of carbon and hydrogen. It is organized into three main families: alkanes (saturated), alkenes and alkynes (unsaturated), and aromatic hydrocarbons. For each family, you will learn their IUPAC nomenclature, methods of preparation, physical properties, and characteristic chemical reactions. The study of structural and geometrical isomerism is also a significant part of this topic.

The core of the chapter is understanding reaction mechanisms. This includes the free-radical substitution of alkanes, electrophilic addition to alkenes and alkynes, and electrophilic substitution in aromatic compounds. You will apply concepts like Markovnikov's rule to predict products. The most challenging part for many students is remembering the specific reagents and conditions for each transformation, such as the Wurtz reaction, ozonolysis, or Friedel-Crafts reactions, and applying electronic effects to predict outcomes.

This chapter heavily relies on 'Organic Chemistry, Some Basic Principles and Techniques'. A solid grasp of nomenclature, isomerism, and electronic effects like the inductive and resonance effects is necessary before starting. Mastering hydrocarbons is essential as it provides the foundation for all subsequent chapters on organic compounds containing functional groups.

Formulas for Hydrocarbons

General formula of alkanes: $C_n H_{2n+2}$ For non-cyclic, saturated hydrocarbons where n ≥ 1.
General formula of alkenes: $C_n H_{2n}$ For non-cyclic hydrocarbons with one double bond, where n ≥ 2.
General formula of alkynes: $C_n H_{2n-2}$ For non-cyclic hydrocarbons with one triple bond, where n ≥ 2.
Wurtz reaction for alkane synthesis: $2R-X + 2Na \xrightarrow{\text{dry ether}} R-R + 2NaX$ R is an alkyl group, X is a halogen. Best for preparing symmetrical alkanes.
Markovnikov's rule for addition to alkenes: $R-CH=CH_2 + HX \rightarrow R-CHX-CH_3$ The negative part of the addendum (X) attaches to the carbon with fewer hydrogen atoms.
Anti-Markovnikov addition (peroxide effect): $R-CH=CH_2 + HBr \xrightarrow{\text{peroxide}} R-CH_2-CH_2Br$ Occurs with HBr in the presence of peroxide; the Br adds to the carbon with more hydrogens.
Reductive ozonolysis of an alkene: $R_1R_2C=CR_3R_4 \xrightarrow{1. O_3} \xrightarrow{2. Zn/H_2O} R_1R_2C=O + R_3R_4C=O$ Cleaves the double bond to form aldehydes or ketones.
Huckel's rule for aromaticity: $(4n + 2) \pi \text{ electrons}$ Aromatic compounds are cyclic, planar, and have (4n+2) delocalized π electrons, where n=0, 1, 2...
Friedel-Crafts alkylation of benzene: $C_6H_6 + R-Cl \xrightarrow{\text{Anhyd. } AlCl_3} C_6H_5-R + HCl$ An electrophilic aromatic substitution to add an alkyl group to benzene.
Friedel-Crafts acylation of benzene: $C_6H_6 + R-CO-Cl \xrightarrow{\text{Anhyd. } AlCl_3} C_6H_5-CO-R + HCl$ Adds an acyl group to benzene, forming a ketone. Avoids rearrangement and polyalkylation.