Jul 7, 2016
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Correct any of my statements if they're wrong:

Alkynes are relatively acidic.
This stems from their high s-character.
S-character is acidic because electrons are near the nucleus.
Highly electronegative atoms have a higher affinity for electrons.
A higher affinity for electrons means electrons will be closer to the nucleus of the atom.
This makes the atom an electron acceptor, which counts as a base.

Why then is an alkyne not considered relatively basic? Thanks for the help!
 

theonlytycrane

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A general alkyne has a pKa ~ 25, which is even higher than water. An alkyne is relatively more acidic than an alkane, but it's a fairly weak acid overall. Weak acids can be equally crappy weak bases sometimes too. Know how alkynes compare to alkenes and alkanes, but don't think about any of these as really acidic or basic overall. To deprotonate an alkyne, usually we use a super strong base, which says something.

source: http://www.masterorganicchemistry.com/2010/06/18/know-your-pkas/
 
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aldol16

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A higher affinity for electrons means electrons will be closer to the nucleus of the atom.
This makes the atom an electron acceptor, which counts as a base.

Why then is an alkyne not considered relatively basic? Thanks for the help!
A Lewis acid accepts electrons. A Lewis base donates electrons. I think you have that definition messed up.

In any case, when we talk about basicity, we're talking about the molecule as a whole - that is, can an alkyne accept a proton? It can, but it doesn't really want to because it'll then have a positive charge on an sp2 carbon.