I was assigned the following question and I cannot decide which is the correct answer.
Which is the most stable structure?
(a) pentane-2,4-dione
(b) 4-hydroxypent-4-en-2-one
(c) (Z)-4-hydroxypent-3-en-2-one
(d) (Z)-penta-1,3-diene-2,4-diol
I am confused between options (c) and (d). Both seem to be stable due to resonance, but I think (d) should have more resonance as the oxygen's lone pair in the $\ce{-OH}$ bond will also participate in resonance making it more stable.
But the answer is given as (c).
Could you please explain why (c) is more stable than (d).