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Difficulty: MediumTetrahedral Carbon, Bonding, and Hybridization

In a propyne molecule (CH3−C≡CHCH_3-C\equiv CH), which hybrid orbitals overlap head-on to form the carbon-carbon single bond between the methyl carbon atom and the adjacent triple-bonded carbon atom?

  1. sp3sp^3 and spsp hybrid orbitalsAnswer
  2. B
    sp3sp^3 and sp2sp^2 hybrid orbitals
  3. C
    sp2sp^2 and spsp hybrid orbitals
  4. D
    sp3sp^3 and sp3sp^3 hybrid orbitals

Answer

The carbon-carbon single bond in propyne is formed by the head-on overlap of an sp3sp^3 hybrid orbital from the methyl carbon atom and an spsp hybrid orbital from the adjacent acetylenic carbon atom.
In propyne (CH3−C≡CHCH_3-C\equiv CH), the methyl carbon atom is attached to four atoms via single bonds, giving it a tetrahedral arrangement and sp3sp^3 hybridization. The central carbon atom is involved in a triple bond and one single bond, giving it a linear arrangement and spsp hybridization. Therefore, the single bond connecting these two carbon atoms is a σ\sigma bond formed by the head-on overlap of an sp3sp^3 hybrid orbital from the methyl carbon and an spsp hybrid orbital from the central acetylenic carbon.

Step-by-Step Solution

1
Determine the hybridization state of the methyl carbon atom (CH3−CH_3-).
The methyl carbon atom forms 4 σ\sigma bonds (3 with H atoms, 1 with C), giving it 4 electron domains and a tetrahedral geometry with sp3sp^3 hybridization.
Four equivalent bonding electron domains around a carbon atom require four sp3sp^3 hybrid orbitals.
2
Determine the hybridization state of the adjacent triple-bonded carbon atom (−C≡-C\equiv).
This carbon atom forms 2 σ\sigma bonds (1 with methyl C, 1 with terminal C) and 2 π\pi bonds, giving it 2 electron domains and a linear geometry with spsp hybridization.
Two linear bonding domains around a carbon atom require two spsp hybrid orbitals.
3
Identify the orbitals participating in the σ\sigma single bond between these two carbon atoms.
The σ\sigma single bond is formed by the end-to-end (head-on) overlap of one sp3sp^3 hybrid orbital from the methyl carbon and one spsp hybrid orbital from the acetylenic carbon.
Single bonds (σ\sigma bonds) between hybridized carbon atoms result from direct axial overlap of their respective hybrid orbitals.

Key Concept

Orbital Overlap and Carbon Hybridization in Alkynes
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Topics

Tetrahedral Carbon, Bonding, and Hybridization

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