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Difficulty: HardTetrahedral Carbon, Bonding, and Hybridization

Consider the organic compound 3-methylbut-1-yne, which has the condensed structural formula HC≡C−CH(CH3)2HC\equiv C-CH(CH_3)_2. How many carbon atoms in a single molecule of this compound are sp3sp^3 hybridized?

Answer: 3 / three / 3 carbon atoms / 3 carbons

Answer

There are 3 sp3sp^3 hybridized carbon atoms in one molecule of 3-methylbut-1-yne.
In 3-methylbut-1-yne (HC≡C−CH(CH3)2HC\equiv C-CH(CH_3)_2), there are 5 total carbon atoms. The two terminal/alkyne carbons (C1C_1 and C2C_2) participate in a triple bond, giving them 2 σ\sigma bonds each and an spsp hybridization state. The central methine carbon (C3C_3) is bonded to four distinct atoms (C2C_2, HH, and two methyl carbons) via single σ\sigma bonds, making it sp3sp^3 hybridized. The two methyl group carbons (C4C_4 and C5C_5) are each single-bonded to three hydrogen atoms and C3C_3, making them sp3sp^3 hybridized as well. Thus, exactly 3 carbon atoms are sp3sp^3 hybridized.

Step-by-Step Solution

1
Expand the condensed structural formula to identify every carbon atom and its bonding environment.
The expanded structure is H−C1≡C2−C3H(C4H3)(C5H3)H-C_1 \equiv C_2 - C_3H(C_4H_3)(C_5H_3), containing a total of 5 carbon atoms.
Expanding the formula clarifies the number of single (σ\sigma) and multiple bonds connected to each carbon atom.
2
Determine the hybridization state of the triply bonded carbon atoms (C1C_1 and C2C_2).
C1C_1 and C2C_2 are each involved in one triple bond and one single bond, forming 2 σ\sigma bonds and 2 π\pi bonds. Thus, both C1C_1 and C2C_2 are spsp hybridized.
A carbon atom with 2 steric domains (linear geometry) uses spsp hybrid orbitals.
3
Determine the hybridization state of the methine carbon atom (C3C_3) and the two methyl carbon atoms (C4C_4 and C5C_5).
C3C_3 forms four single σ\sigma bonds (one to C2C_2, one to HH, and two to methyl carbons). C4C_4 and C5C_5 each form four single σ\sigma bonds (one to C3C_3 and three to HH). Therefore, C3C_3, C4C_4, and C5C_5 are all sp3sp^3 hybridized.
A carbon atom bonded to 4 separate atoms via single σ\sigma bonds has 4 steric domains (tetrahedral geometry) and undergoes sp3sp^3 hybridization.
4
Count the total number of sp3sp^3 hybridized carbon atoms.
3 carbon atoms (C3C_3, C4C_4, and C5C_5) are sp3sp^3 hybridized.
Combining the results from steps 2 and 3 gives 2 spsp carbons and 3 sp3sp^3 carbons.

Key Concept

Identification of carbon hybridization states (sp3,sp2,spsp^3, sp^2, sp) in aliphatic molecules
Estimated Time:1m 30s
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Topics

Tetrahedral Carbon, Bonding, and Hybridization

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