In the context of degrees of unsaturation, a carbon-carbon triple bond contributes how many degrees of unsaturation to a molecule?

• A. $1$
• B. $3$
• C. $0$
• D. $2$

Answer: (D)

Verified step by step guidance

1. Recall that the degree of unsaturation (also called the index of hydrogen deficiency) measures the total number of rings and multiple bonds in a molecule.
2. Understand that each degree of unsaturation corresponds to the loss of two hydrogen atoms compared to the fully saturated alkane formula \(C_nH_{2n+2}\).
3. Recognize that a double bond contributes one degree of unsaturation because it reduces the hydrogen count by two.
4. Know that a triple bond involves two pi bonds between the same two carbons, which means it reduces the hydrogen count by four compared to the saturated alkane.
5. Therefore, since each degree of unsaturation corresponds to two fewer hydrogens, a triple bond contributes two degrees of unsaturation.