Organic chemistry is the branch of chemistry that deals with the study of carbon compounds (except simple oxides such as CO and COâ‚‚, carbonates, and carbides). Organic compounds mainly consist of carbon and hydrogen, and may also contain oxygen, sulfur, nitrogen, and halogens. They form the basis of life processes and are found in living organisms, fuels, plastics, detergents, drugs, and more.
Carbon is unique because it forms a very large number of compounds — over 10 million known — due to:
| Properties of Carbon in Organic Chemistry | |
|---|---|
| Tetravalency | Carbon has 4 valence electrons and forms 4 stable covalent bonds. |
| Catenation | Carbon atoms bond with themselves to form long chains, branches, and rings. |
| Formation of multiple bonds | Carbon forms C–C, C=C and C≡C bonds with great stability. |
| Hybridization | Carbon mixes orbitals (sp³, sp², sp) to form different molecular shapes. |
Organic compounds share certain characteristics that differentiate them from inorganic compounds.
| Unique Property | Description |
|---|---|
| Low melting and boiling points | Organic compounds are usually covalent and have weak intermolecular forces. |
| Combustibility | Most organic compounds burn in air to produce COâ‚‚ and Hâ‚‚O. |
| Isomerism | Organic molecules can have the same formula but different structures. |
| Stability | Most organic compounds are thermally unstable and decompose on heating at high temperature leaving behind a black char of carbon. |
| Nature | Organic compounds are covalent in nature |
| Flammability | Organic compounds are generally flammable producing lots of heat . |
Hybridization is the process by which carbon mixes its atomic orbitals (2s and 2p) to form new orbitals of equal energy called hybrid orbitals. Hybridization determines the shape of organic molecules.
1. sp³ Hybridization: This occurs when one 2s orbital mixes with three 2p orbitals of carbon to form four identical sp³ hybrid orbitals. Each sp³ orbital contains one unpaired electron and forms a sigma (σ) bond with another atom. The four sp³ orbitals arrange themselves as far apart as possible, forming a tetrahedral shape with bond angles of 109.5°. An example is methane (CH₄), where carbon forms four single bonds with hydrogen atoms. The tetrahedral geometry allows for maximum separation between electron pairs, minimizing repulsion.
2. sp² Hybridization: In this type, one 2s orbital mixes with two 2p orbitals to form three sp² hybrid orbitals, leaving one unhybridized p orbital. The three sp² orbitals form sigma (σ) bonds in a plane, giving the molecule a trigonal planar shape with bond angles of 120°. The remaining unhybridized p orbital forms a pi (π) bond with another p orbital, creating a double bond. An example is ethene (C₂H₄), where each carbon forms three sigma bonds (two with hydrogen, one with carbon) and one pi bond (C=C).
3. sp Hybridization: This occurs when one 2s orbital mixes with only one 2p orbital to form two sp hybrid orbitals, leaving two unhybridized p orbitals. The sp orbitals are arranged linearly, 180° apart, forming sigma (σ) bonds, while the two unhybridized p orbitals overlap sideways to form two pi (π) bonds, resulting in a triple bond. An example is ethyne (C₂H₂), where each carbon forms two sigma bonds (one with hydrogen, one with carbon) and two pi bonds (C≡C). The linear shape minimizes electron repulsion between the orbitals.
| Type | Bonding | Shape | Bond Angle | Example |
|---|---|---|---|---|
| sp³ | Four sigma (σ) bonds | Tetrahedral | 109.5° | CH₄ (Methane) |
| sp² | Three sigma + one pi (π) bond | Trigonal planar | 120° | C₂H₄ (Ethene) |
| sp | Two sigma + two pi (π) bonds | Linear | 180° | C₂H₂ (Ethyne) |
Summary:
- sp³ → 4 sigma bonds, tetrahedral, bond angle 109.5°, single bonds (alkanes)
- sp² → 3 sigma + 1 pi bond, trigonal planar, bond angle 120°, double bonds (alkenes)
- sp → 2 sigma + 2 pi bonds, linear, bond angle 180°, triple bonds (alkynes)
Hybridization explains the shape and bonding patterns in organic molecules and is essential for understanding their chemical behavior.