Consider the three hydrocarbons listed below, each capable of acting as a very weak Brønsted–Lowry acid.
I. Propyne, HC≡CCH3
II. Allyl alcohol, CH2=CHCH2OH
III. Propene, CH3CH=CH2
Use structural arguments to compare their acidities.
(a) For the conjugate base derived from each molecule, state whether the negative charge can be stabilized beyond the atom on which it originates. Identify the specific mechanism of any stabilization.
(b) Rank the three molecules from most acidic (1) to least acidic (3).
(c) Provide a thorough explanation for the ranking in part (b), commenting on why one of the molecules is considerably less acidic than the others despite being unsaturated.