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Chemistry

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    $\begingroup$ It does react, for example in the formation of enol ethers, and technically the protonation of a carbonyl group is also an example. It's a much harder nucleophile than the alpha carbon and therefore reacts with different things. $\endgroup$
    – orthocresol
    Commented Sep 27, 2015 at 14:23
  • $\begingroup$ >Is there any reason for the low reactivity of the oxygen? || Yes. It is in $sp^2$ hybridization state, meaning it binds its lone pairs extremely strong. It seems, however, that it can react with strong electrophyles like proton. It also should act as one in synthesis of pyrilium salts, but I was unable to find a proposed mechanism. Also, technically the nucleophilic oxygen in Wittig synthesis is derived from carbonyl oxygen, but is not one at the moment of attack $\endgroup$
    – permeakra
    Commented Sep 27, 2015 at 20:57
  • $\begingroup$ @orthocresol Isn't protonation of the carbonyl an acid-base reaction though? (i.e. not a nucleophile-electrophile reaction) $\endgroup$
    – SasQ
    Commented Nov 18, 2021 at 0:49
  • $\begingroup$ @SasQ Those labels aren't mutually exclusive. H+ is an electrophile, and anything that gets protonated is acting as a nucleophile towards it. $\endgroup$
    – orthocresol
    Commented Nov 18, 2021 at 0:50
  • $\begingroup$ Well, in that case we would have to treat the entire conjugate base as a leaving group that leaves the proton, wouldn't we? $\endgroup$
    – SasQ
    Commented Nov 18, 2021 at 1:17