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Chapter 17

CHMB42 Chapter 17


Department
Chemistry
Course Code
CHMB42H3
Professor
Wanda/ Lana
Chapter
17

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Chapter 17: Carbonyl Compounds II
Nomenclature of Aldehydes and Ketones
The systematic name of an aldehyde is obtained by replacing the final “e” on
the name of the parent hydrocarbon with “al” (ethanal, 2-bromopropanal or
methanal).
Terminal “e” is removed only to avoid two successive vowels (hexanedial, e
isn’t removed).
If a compound has two functional groups, the one with the lower priority is
indicated by a prefix and the one with the higher priority by a suffix.
The systematic name of a ketone is obtained by replacing the final “e” on the
end of the name of the parent hydrocarbon with “one.”
The chain is numbered in the direction that gives the carbonyl carbon the
smallest number (3-hexanone, 6-methyl-2-heptanone or acetone).
If the ketone has a second functional group of higher naming priority, the
ketone oxygen is indicated by the prefix “oxo.”
Increasing Priority: Alkyl Halide < Ether < Alkane < Alkyne < Alkene < Amine <
Alcohol < Ketone < Aldehyde < Nitrile < Amide < Ester < Carboxilic Acid
Relative Reactivities of Carbonyl Compounds
Since a hydrogen is electron withdrawing compared to an alkyl group, an
aldehyde is more reactive than a ketone toward nucleophilic attack
(formaldehyde < aldehyde < ketone).
Steric factors also contribute to the greater reactivity of an aldehyde, making
the carbonyl carbon of an aldehyde more accessible to the nucleophile than is
the carbonyl carbon.
Relative Reactivities of Carbonyl Compounds: Acyl Halide > Acid Anhydride >
Aldehyde > Ketone > Ester ~ Carboxylic Acid > Amide > Carboxylate Ion.
Aldehydes and ketones are not as reactive as carbonyl compounds in which Y- is
a very weak base but more reactive in which Y- is a relatively strong base.
How Aldehydes and Ketones React
Aldehydes and ketones do not undergo acyl substitution reactions.
Nucleophilic Addition Reaction: irreversible reaction when a nucleophile adds to
the carbonyl group of an aldehyde or a ketone and nothing is expelled due to
nucleophile being a strong base.
If the nucleophile is a relatively weak base, the product of the reaction will
again be the tetrahedral compound but reversible.
Nucleophilic Addition-Elimination Reaction: if the attacking atom of the
nucleophile has a lone pair and there is sufficient acid to protonate the OH
group of the tetrahedral compound, water can be eliminated from the addition
product (reversible).
Reactions of Carbonyl Compounds with Grignard Reagents
Addition of a Grignard reagent to carbonyl compounds leads to the formation of
a new C-C bond, with the Grignard reagent acting as a nucleophile that’s a
strong base.
Aldehydes and ketones undergo nucleophilic addition reactions with Grignard
reagents.
When a Grignard reagent (RMgX) reacts with formaldehyde, the addition
product is a primary alcohol.
When a Grignard reagent (RMgX) reacts with an aldehyde other than
formaldehyde, the addition product is a secondary alcohol.

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When a Grignard reagent (RMgX) reacts with a ketone, the addition product is a
tertiary alcohol.
In a Grignard reagent, the R group acts as a nucleophile attacking the C in C=O.
A Grignard reagent can also react with carbon dioxide, giving a carboxylic acid
as a product that has more than one carbon atom than the Grignard reagent.
Class I carbonyl compounds (ester or acyl chloride) undergo two successive
reactions with the Grignard reagent (nucleophilic acyl substitution reaction then
a nucleophilic addition reaction).
oNucleophilic attack by the Grignard reagent forms a tetrahedral
intermediate that is unstable because it has a group that can be
expelled.
oThe tetrahedral intermediate expels methoxide ion, forming a ketone.
The reaction doesn’t stop at the ketone stage because ketones are more
reactive than esters toward nucleophilic attack.
oReaction of the ketone with a second molecule of the Grignard reagent,
followed by protonation of the alkoxide ion, forms a tertiary alcohol.
oThe alcohol should have two identical alkyl groups bonded to the tertiary
carbon.
Reactions of Carbonyl Compounds with Acetylide Ions
Terminal alkyne can be converted into an acetylide ion: CH3CCH + NaNH2/NH3
CH3CC-.
Acetylide ions are strong bases that react with a carbonyl compound to form a
nucleophilic addition product (adds a new C-C bond), then a weak acid is added
to the reaction mixture to protonate the alkoxide ion.
Reactions of Carbonyl Compounds with Hydride Ion
A hydride ion is another strongly basic nucleophile that reacts with aldehydes
and ketones to form nucleophilic addition products.
Mechanism for the reaction of an aldehyde or a ketone with hydride ion
(NaBH4):
oAddition of a hydride ion to an aldehyde or ketone form an alkoxide ion
(the H- ion attacks the C in C=O).
oSubsequent protonation by an acid produces an alcohol. The overall
reaction adds H2 to the carbonyl group.
oReduction Reaction: addition of a hydrogen to a compound.
Mechanism for the reaction of an acyl chloride with hydride ion:
oThe acyl chloride undergoes a nucleophilic acyl substitution reaction
because it has a group that can be replaced by hydride ion; produces an
aldehyde.
oThe aldehyde undergoes a nucleophlic addition reaction with a second
equivalent of hydride ion, forming an alkoxide ion, which, when
protonated, gives a primary alcohol.
Lithium aluminum hydride (LiAlH4) is more reactive than sodium borohydride
(NaBH4) so it reduces all carbonyl groups; sodium borohydride only reduces
aldehydes and ketones.
Lithium aluminum hydride produces two alcohols, one corresponding to the acyl
portion of the ester and one corresponding to the alkyl portion.
The mechanism for esters is the same as the mechanism for acyl chlorides but
gives two alcohols as products.
Diisobutylaluminum Hydride (DIBALH): used as the hydride donor at a low
temperature of -780C so the reaction can be stopped after the addition of one
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