Hydrocarbons and Substitution Reactions

Study Notes

Hydrocarbons are the simplest organic compounds that contain only carbon and hydrogen.
They can be found naturally in crude oil, where decomposed organic matter provides an abundance of carbon and hydrogen.
Hydrocarbons can be classified as saturated or unsaturated, and can have open chain (aliphatic) or closed chain (cyclic) structures.

Saturated hydrocarbons are characterized by the presence of only sigma (σ) bonds, hence, the carbon atoms are all single-bonded.
They include alkanes (-C-) and cycloalkanes.
Saturated hydrocarbons are generally inert towards HCl, H2SO4, oxidizing agents like KMnO4 and Na2Cr2O7 at room temperature.
They are non-polar compounds that do not react with ionic compounds such as laboratory acids, bases, oxidizing agents or reducing agents.

Alkanes contain only single C-C and C-H bonds.
They have the maximum number of hydrogens bonded to each carbon.
Acyclic alkanes contain chains of C atoms (CnH2n+2), while cycloalkanes contain carbon atoms arranged in a ring (CnH2n).
Physical properties: alkanes have nonpolar C-C and C-H bonds, are insoluble in water, and soluble in non-polar organic compounds.
They have low melting and boiling points, which increase as the number of carbons increases.
Alkanes exhibit weak intermolecular forces (van der waals or London Dispersion Force).
They exhibit isomerism.

Alkanes have no functional group, so they undergo few reactions.
Complete combustion reaction: alkanes burn in the presence of O2 gas to form CO2 and H2O, producing a non-luminous flame.

Unsaturated hydrocarbons include alkenes (C=C) that contain at least one pi bond (π).
They also include alkynes, cycloalkenes, cycloalkynes, and aromatic compounds (containing a benzene ring).
Unsaturated hydrocarbons undergo addition reactions at the double bond, which is detected by Baeyer's test.
Aromatic compounds exhibit resonance, resulting in conjugative stability of the molecule.
They resist addition to the pi bonds but readily undergo electrophilic aromatic substitution.

Based on the number of carbons attached to the central carbon:
- Primary carbon is bonded to one other C.
- Secondary carbon is bonded to two other C.
- Tertiary carbon is bonded to three other C.
- Quaternary carbon is bonded to four other C.