The best replacement for carbonyl is carboxyl.

The best alternatives to carbonyl are rated as following:
★★★★★  carboxyl
★★★★★  ketone
★★★  carboxyl group
★★  acyl
★★  ferrous sulfate

Your alternative for carbonyl is not listed? Suggest!
Speaking about carbonyl, one probably shouldn't forget about amine.

Other search terms related to carbonyl and their ratings are:
★★★★★ amine
★★★★ nh2
★★★ grignard
★★ hydrazine
★ sodium borohydride
You have in mind a companion for carbonyl and it is not yet here? Propose!



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carbonyl
carboxyl
ketone