09 Aldehydes and Ketones Free Online FlashCards

What structural feature defines an aldehyde?

An aldehyde has a carbonyl carbon bonded to at least one hydrogen: $\mathrm{R{-}CHO}$.

What is the geometry around a carbonyl carbon?

The carbonyl carbon is $\mathrm{sp^2}$-hybridized and trigonal planar.

Where does a nucleophile attack a carbonyl group?

Nucleophiles attack the electrophilic carbonyl carbon.

What happens to the carbonyl during nucleophilic addition?

The nucleophile bonds to the carbonyl carbon as the $\mathrm{C{=}O}$ $\pi$ electrons shift to oxygen, forming a tetrahedral alkoxide intermediate.

What alcohol forms when an aldehyde is reduced?

Hydride addition followed by protonation converts an aldehyde into a primary alcohol: $\mathrm{R{-}CHO \rightarrow R{-}CH_2OH}$.

What structural feature defines a ketone?

A ketone has a carbonyl carbon bonded to two carbon groups: $\mathrm{R{-}CO{-}R'}$.

How is charge distributed across a carbonyl bond?

The $\mathrm{C{=}O}$ bond is polarized: oxygen is partially negative, $\delta^-$, and carbon is partially positive, $\delta^+$.

Why are aldehydes generally more reactive than ketones?

Aldehydes are generally more reactive because they have less steric crowding and less electron donation to the carbonyl carbon than ketones.

Why is carbonyl nucleophilic addition not substitution?

It is addition because the nucleophile adds and the $\mathrm{C{=}O}$ $\pi$ bond becomes a $\mathrm{C{-}O}$ single bond; there is usually no suitable leaving group.

How can acid promote carbonyl addition by a weak nucleophile?

Protonating the carbonyl oxygen increases the electrophilicity of the carbonyl carbon, enabling attack by a weaker nucleophile such as water.

What alcohol forms when a ketone is reduced?

Hydride addition followed by protonation converts a ketone into a secondary alcohol: $\mathrm{R{-}CO{-}R' \rightarrow R{-}CH(OH){-}R'}$.

What is a common mild reagent for reducing aldehydes and ketones?

$\mathrm{NaBH_4}$ is a common, comparatively mild reagent for reducing aldehydes and ketones.