Aldehydes and Ketones Flashcards
Reaction with a primary amine gives an…
Imine
- an organic compound containing the group —C=NH or —C=NR where R is an alkyl or other group.
Reaction with a secondary amine gives an…
Enamine
- An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates. The word “enamine” is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group containing both alkene (en-) and alcohol (-ol). Enamines are considered to be nitrogen analogs of enols.
Which is the more acidic carboxylic acids and why?
Which is the more acidic carboxylic acids and why?
Explain the following relative order of reactivity; this trend is observed whenever these carbonyl compounds react with nucleophiles.
Rank the following carboxylic acid derivatives in order of decreasing reactivity with nucleophiles and explain briefly.
Reactivity is correlated to the ability of an adjacent lone pair to donate into the π*CO of the carbonyl.
- Esters are less reactive than acid chlorides, because the O lone pair (2p) is a much better donor than the Cl lone pair (3p).
- Among the esters, an electron-withdrawing group on the aromatic ring reduces the electron density on the O, making it a worse donor and increasing reactivity of the carbonyl. An electron-donating group on the aromatic ring increases electron density on O, making it a better donor and decreasing reactivity of the carbonyl.
- Amides are less reactive than esters because N is less electronegative than O, so the N lone pair is a better donor than the O lone pair. Nitriles are even less reactive since π*CN is a worse acceptor than π*CO .
- Carboxylates are least reactive because the O lone pair is an excellent donor and because the negative charge repels electron-rich nucleophiles.
Match the carboxylic acids below with the pK a values listed at right. Explain your ranking.
In general, EWGs stabilize the carboxylate anion conjugate base by induction, favoring dissociation and leading to a stronger acid. Thus more EWGs on an acid make it stronger. By the same token, the closer the EWGs are to the carboxylate, the better they are able to stabilize it (inductive effects exert their force through the sigma bond framework of molecules, thus they diminish rapidly with increasing distance).
Explain the trend in pKa values observed for formic acid, acetic acid, and carbonic acid, respectively.
