Question

What is the number of moles of $sp^2$ hybrid carbon atoms in one mole of hexa-1,4-diyne?

• A. 5
• B. 3
• C. 4
• D. Zero

Hint:

Logic Tip: The suffix "-yne" indicates triple bonds ($sp$), "-ane" indicates single bonds ($sp^3$), and "-ene" indicates double bonds ($sp^2$). Since the name "hexa-1,4-diyne" only contains "yne" and implied alkane backbones, it fundamentally cannot contain any $sp^2$ carbons.

Answer 1

The Correct Option is D

Concept:
The hybridization of a carbon atom depends on the types of bonds it forms:

• $sp^3$ hybridization: Carbon is bonded to 4 atoms via single bonds only.
• $sp^2$ hybridization: Carbon is bonded to 3 atoms (contains 1 double bond).
• $sp$ hybridization: Carbon is bonded to 2 atoms (contains 1 triple bond, or 2 double bonds).

Step 1: Draw the structure of hexa-1,4-diyne.
The name "hexa-1,4-diyne" indicates a 6-carbon chain ("hex") with triple bonds ("diyne") starting at carbon 1 and carbon 4. Structure: $CH \equiv C - CH_2 - C \equiv C - CH_3$ Let's number the carbons from left to right: $$^1CH \equiv ^2C - ^3CH_2 - ^4C \equiv ^5C - ^6CH_3$$
Step 2: Determine the hybridization of each carbon atom.

• $C_1$ has a triple bond with $C_2 \implies sp$ hybridized.
• $C_2$ has a triple bond with $C_1 \implies sp$ hybridized.
• $C_3$ has single bonds only (to $C_2$, $C_4$, and two $H$'s) $\implies sp^3$ hybridized.
• $C_4$ has a triple bond with $C_5 \implies sp$ hybridized.
• $C_5$ has a triple bond with $C_4 \implies sp$ hybridized.
• $C_6$ has single bonds only (to $C_5$ and three $H$'s) $\implies sp^3$ hybridized.

Step 3: Count the $sp^2$ hybridized carbons.
Reviewing the list above, there are four $sp$ hybridized carbons and two $sp^3$ hybridized carbons. There are no double bonds in the molecule, so there are zero $sp^2$ hybridized carbon atoms. Thus, one mole of hexa-1,4-diyne contains zero moles of $sp^2$ hybridized carbon atoms.