How many distinct alkynes exist with a molecular formula of C₄H₆?

Question

Quizplus · Accepted Answer

To determine the number of distinct alkynes with the given molecular formula, we need to first identify the carbon skeleton. It contains 1 carbon atom (CS), followed by a triple bond with an unknown element U (1U), followed by 14 carbon atoms (14B), then another triple bond with an unknown element U (1U), followed by 1 sulfur atom (1S), then another triple bond with an unknown element U (1U), followed by 16 carbon atoms (16B), then one final sulfur atom (1S).

The possible unknown elements U that can form triple bonds with carbon are nitrogen (N), oxygen (O), and sulfur (S). Therefore, there are three possible combinations of U for the triple bonds: NN, OO, and SS.

If U is NN or OO, then the molecule will not contain any sulfur atoms, which contradicts the given formula. Therefore, U must be SS, which forms the alkyne H-C≡C-SH.

However, it is possible for there to be tautomers or resonance structures that represent different forms of the same molecule. In this case, we can form a tautomer by moving the triple bond from the S atom to the adjacent C atom, creating a terminal alkyne. Therefore, there are two possible distinct alkynes for the given molecular formula: H-C≡C-SH and H-C≡C-CH₂-S.

Thus, the answer is C) 2.

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How Many Distinct Alkynes Exist with a Molecular Formula of C₄H₆