The bond angle of a carbon atom depends on its hybridization and the molecular geometry.
Carbon Bond Angles Based on Hybridization
The most common bond angles for carbon are determined by its hybridization state:
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sp3 Hybridization (Tetrahedral): When a carbon atom is bonded to four other atoms, it adopts a tetrahedral geometry. The bond angle in this arrangement is approximately 109.5°. Methane (CH4) is a classic example.
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sp2 Hybridization (Trigonal Planar): When a carbon atom is bonded to three other atoms and has one pi bond (e.g., in alkenes), it adopts a trigonal planar geometry. The bond angle in this arrangement is approximately 120°. Ethene (C2H4) is an example.
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sp Hybridization (Linear): When a carbon atom is bonded to two other atoms and has two pi bonds (e.g., in alkynes), it adopts a linear geometry. The bond angle in this arrangement is 180°. Ethyne (C2H2) is an example.
Factors Affecting Bond Angles
While the above values are ideal, several factors can influence the actual bond angle:
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Lone Pairs: The presence of lone pairs of electrons on adjacent atoms can compress the bond angles. However, carbon does not commonly have lone pairs in stable organic molecules.
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Steric Hindrance: Bulky substituents can also affect bond angles, causing them to deviate from the ideal values to minimize steric strain.
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Ring Strain: Cyclic molecules, especially small rings like cyclopropane, can have significantly distorted bond angles due to ring strain. Cyclopropane has bond angles of approximately 60°, which deviate significantly from the ideal tetrahedral angle of 109.5°.
In summary, while carbon can have different bond angles depending on the specific molecule, the "normal" valence angle for a tetrahedrally bonded carbon (sp3 hybridization) is 109.5°.
