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Chem 1152: Ch. 14
Aldehydes and Ketones
IntroductionIntroduction
Aldehyde: Carbonyl group with one or two H attached.•Named by replacing –e with –al (IUPAC).•The aldehyde C is always numbered as 1.
O
R H
O
R R
O
H H
Ketone: Carbonyl group with two C attached.•Named by replacing –e with –one (IUPAC).•Numbered from end closest to carbonyl group
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Common Aldehydes and KetonesCommon Aldehydes and Ketones
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Naming AldehydesNaming Aldehydes
O
HCH3
pentanal
Cl
O
H
5-chloropentanal
H O
CH3CH3
2-ethylbutanal
CH3
O
H
CH3
CH3
3,4-dimethylhexanal
Cl
CH3 O
H
5-chloro-2-methylbenzaldehyde
Cl
O
H
m-chloro-benzaldehyde
CH3
O
CH3 O
H
5-methoxy-2-methylbenzaldehyde
Drawing AldehydesDrawing Aldehydes
2-bromo-2-methylpropanal
2-hydroxy-5-methoxybenzaldehyde
CH3
O
OH O
H
Br H
O
3-bromo-4-phenylbutanal
BrCH3
H
O
CH3
3-chloropentanal
CH3
Cl
H
O
Naming KetonesNaming Ketones
2-pentanone 5-chloro-2-pentanone 1-chloro-3-pentanone
4-ethylcyclohexanone 2-fluoro-5-methyl-4-octanone
O
CH3 CH3
Ketone: Carbonyl group with two C attached.•Named by replacing –e with –one (IUPAC).•Numbered from end closest to carbonyl group
ClO
CH3
O
Cl
CH3
O
CH3CH3
F O
CH3
CH3
Physical PropertiesPhysical Properties
CH3
OH
CH3 CH3
CH3
OCH3
O
CH3 H
Carbonyl O cannot form H-bonds between molecules, but can form weaker dipolar bonds. Carbonyl O can form H-bonds with water (polar solvent) for low MW ketones and aldehydes.
BP values lower than similar alcohols, but higher than those of alkanes.
O
R R
O
R R
δ-
δ-
δ+
δ+
Intermoleculardipolar
H HO
Hydrogen bond δ+
δ-
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Hydrogenation Rxn – AldehydesHydrogenation Rxn – AldehydesAldehyde hydrogenation rxnAldehyde hydrogenation rxn
Alcohol oxidation rxnAlcohol oxidation rxn
H-OH+RC
O
HH
H
(O)+ R C
O
H
(O)R C
O
OH
Carboxylic acid
Primary alcoholaldehyde
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Hydrogenation Rxn – AldehydesHydrogenation Rxn – AldehydesAldehyde hydrogenation rxnAldehyde hydrogenation rxn
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
butanal
CH3
O
H
CH3
CH3
3,4-dimethylhexanal
+ H HPt
O
HCH3
+ H HPt
O
HCH3
HH
O
HCH3
1-butanol
CH3 HH
O
CH3
CH3 H
3,4-dimethyl-1-hexanol
Hydrogenation Rxns – KetonesHydrogenation Rxns – KetonesKetone hydrogenation rxnKetone hydrogenation rxn
H-OH+RC
O
HR
H
(O)+ R C
O
R
Secondary alcohol ketone
Alcohol oxidation rxnAlcohol oxidation rxn
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Hydrogenation Rxns – KetonesHydrogenation Rxns – Ketones
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
+ H HPt
O
CH3CH3
HH
O
CH3CH3
2-butanone 2-butanol
Ketone hydrogenation rxnKetone hydrogenation rxn
+ H H
Pt
CH3CH3
CH3
OCH3
H CH3
CH3
CH3
OH
CH3
4,4-dimethyl-3-hexanone
4,4-dimethyl-3-hexanol
Addition of alcohol to aldehydes and ketonesAddition of alcohol to aldehydes and ketones
Hemiacetal is unstable, hard to isolate. With excess alcohol and an acid catalyst, a stable acetal is formed.
Note the bidirectional arrows
O
R H
+ H
R
O
RO
HO
R H
H+, RO-H
RO
RO
R H + H-O-H
Hemiacetal Hemiacetal intermediateintermediate
acetalacetal
O
R R
+ H
R
O
RO
HO
R R
H+, RO-H
RO
RO
R R + H-O-H
Hemiketal Hemiketal intermediateintermediate
ketalketal
Hydrolysis of acetals and ketalsHydrolysis of acetals and ketals
“Cutting by water” is essentially the reverse of the addition of alcohol to either aldehyde or ketone.
aldehydealdehydeacetalacetal
RO
RO
R H +H
H
O H+ O
R H
2 R-OH+
alcoholalcohol
ketoneketoneketalketal alcoholalcohol
RO
RO
R R +H
H
O H+ O
R R
2 R-OH+
Intramolecular addition of alcohols to aldehydeIntramolecular addition of alcohols to aldehyde
C1 is hemiacetal carbon. Attached to it you will find: H, OH, OR and R, just like non-cyclical compounds.
Intramolecular Intramolecular hemiacetalhemiacetalglucoseglucose
C
C
C
C
CH2
C
OH
OH
OH
OH
HO H
H
H
H
H O1
2
3
4
5
6
*CH2OH
C
C
C C
O
C
6
5
4
3 2
1
OH
H
OH
OH
OH
H
H
H
HR
Aldehyde Rxns – Testing for AldehydesAldehyde Rxns – Testing for Aldehydes
Benedict’s Reagent reacts with ketones that have an alcohol on the adjacent carbon (e.g., glucose)
Products include a red precipitate of copper (I) oxide
Tollens’ Reagent (reacts with all aldehydes, but not ketones)Tollens’ Reagent (reacts with all aldehydes, but not ketones)
Benedict’s Reagent (reacts with aldehydes, alpha-hydroxy ketones)Benedict’s Reagent (reacts with aldehydes, alpha-hydroxy ketones)