Question

among the following organic compounds. which is most acidic ? Methane,acetylene,But-l-ene

Answer 1

acetylene is the most acidic compound

Answer 2

Answer:Acetylene

Explanation: First, write the molecular formulas and identify the hybridization of the carbon atoms (C):

Methane = CH4: Csp3

1-butene = H3C−CH2−CH=CH2: has Csp2 and Csp3

Acetylene = HC≡CH: Csp

According to Clayden’s Organic Chemistry:

“The hybridization of the orbital from which the proton is removed also affects the pKa. Since s orbitals are held closer to the nucleus than are p orbitals, the electrons in them are lower in energy, that is, more stable. Consequently, the more s character an orbital has, the more tightly held are the electrons in it. This means that electrons in an sp orbital (50% s character) are lower in energy than

those in an sp2 orbital (33% s character), which are, in turn, lower in energy than those in an sp3 orbital (25% s character). Hence the anions derived from ethane,

ethene, and ethyne increase in stability in this order and this is reflected in their pKas”.

In your case, acetylene (C sp) would be more acidic.