[jestquim]

 In a problem bulletin, the following exercise has been proposed to me:

1. Indicate whether the following statements are true or false. Justify your answer:

(a) Alkynes, in general, are less reactive than alkenes.
b) In nucleophilic addition, ketones have, mostly, a higher reaction rate than aldehydes.
c) Fisher esterification is the method with the highest yield for the synthesis of esters.
d) The reaction of a terminal alkyne with potash (KOH) produces an acetylide salt.
e) The following acids are ordered from highest to lowest acidity: trichloroacetic acid > dichloroacetic acid > chloroacetic acid > acetic acid.
f) The pKa of phenol is higher than that of meta-chloroperbenzoic acid (mCPBA).

My attempted solution

a) I think the statement is true, because I have it in the class notes. But, I would not know how to justify it correctly.
b) False. Ketones are more sterically hindered than aldehydes, so they undergo such reactions less effectively.
c) False. Fisher esterification is reversible, that is, when we obtain the final product (ester) there are still appreciable amounts of the reactants (carboxylic acid and alcohol) remaining in the reaction medium. A more effective procedure would be the reaction of the acid chloride with the alcohol in pyridine.
d) False. But, I would not know how to justify it.
e) True. I would try to justify it by the inductive -I effect, but the acidity of carboxylic acids messes me up a bit.
f) True. But, I tried to look up a table with pKa values and, on the exam, I wouldn't have access to it. So, I don't know how I would reason this.

I hope you can help me. Thanks!

[Babcock_Hall]

For d) think about the equilibrium of the reaction.

[rolnor]

If alkynes are more acidic then alkenes then  they are more reactive towards base compared to alkenes. How about other reactions, say bromination? Also, how do you define "more reactive" is it lower energy of activation or what?

[Babcock_Hall]

IMO question a) is open-ended.  That having been said, it is also possible that either a true or a false answer could be justified.  Reductions of alkenes vs. alkynes is an interesting case to consider.