Comparing ethyne, ethane and ethene, which of the following is the most acidic?A.EthaneB.EtheneC.EthyneD.All of these molecules have identical acidity

To determine which of the compounds—ethyne, ethene, or ethane—is the most acidic, we need to consider the structure of each molecule and the stability of their conjugate bases:

1. Understanding Acidity: Acidity is often related to the stability of the conjugate base formed after the molecule donates a proton (H⁺). The more stable the conjugate base, the stronger the acid.

2. Analyzing the Compounds:

   • Ethyne (C₂H₂): This alkyne has sp hybridization for the carbon atoms. When it loses a proton, it forms the acetylide ion (C₂H⁷⁻), which is stabilized by the high s-character of the sp hybridized carbon, resulting in stronger acidity.
   • Ethene (C₂H₄): This alkene has sp² hybridization. Upon losing a proton, it forms an anion (C₂H₄H⁻) that has less stability compared to the acetylide ion from ethyne due to the higher hybridization and less s-character.
   • Ethane (C₂H₆): This alkane has sp³ hybridization, resulting in lower acidity. The conjugate base formed (C₂H₅H⁻) is even less stable than the anion from ethene as it has the least s-character.

3. Stability of Conjugate Bases: The order of acidity can be deduced as follows:

   • Ethyne > Ethene > Ethane
   • This indicates that ethyne is the most acidic due to the stability of the acetylide ion formed after proton donation.

Final Answer

C. Ethyne is the most acidic among ethyne, ethene, and ethane.