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19
The position of the equilibrium between gem diols and aldehydes / ketones depends on the structure of the carbonyl compound.
+
H OH H NH-NH2 XMg R''
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1. React with HCN (hydrocyanic acid)
Aldehydes and ketones react with HCN to produce cyanohydrins (氰醇). The nucleophilic cyanide ion adds to the electrophilic carbonyl carbon.
Nucleophilic oxygen reacts - with acids and electrophiles
O ——C———C H
(2) Activity of -hydrogen
+ (1) Electrophilic carbon reacts with bases and nucleophiles
OH R C H( CH3 ) CN 氰醇
This reaction is only suitable to the aldehydes, alkyl methylketones, and cycloketones (C≤8) (醛、脂肪族甲基酮、8C以下环酮适用)
H
activity
H
C=O
> H C=O > (
CHO
CHO
Cyclohexanecarbaldehyde 2-Naphthalenecarbaldehyde 环己基甲醛 2-萘甲醛 (3) Aromatic aldehydes are also named as derivatives of the parent benzaldehyde. benzaldehyde
+
O
C
H H ( :Nu H H H
-
： CN ： SO3Na ) ： OR H+ ： OH + (E ) ： NH-G
O-H C
Nu
XMg： R Cyanide ion(CN-), bisulphite anion, alcohols, H2O, ammonia and carbon anions (R3C-) are several of many possibilities.
CHO
O C- CH 3
2
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Ⅱ. Nomenclature
1. Aldehydes
(1) The IUPAC names for aldehydes are derived from the parent hydrocarbon by identifying the longest chain containing the aldehyde group (-CHO) and replacing the ‘-e’ ending with ‘-al’.
O CH3
3-Methylcyclohexanone
(3) Ketones in which the carbonyl group is attached directly to a benzene ring are named as phenyl derivatives of the corresponding aliphatic carbonyl compound.
CH3 O O CH3CH CHC H 4 3 2 1 2-Butenal
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CH3CHCH2CH2C H 5 4 3 2 1 4-Methylpentanal
(2) For more complex aldehydes in which the –CHO group is attached to a ring, the suffix –carbaldehyde is used.
第 9 章 醛 和 酮
Chapter 9 Aldehydes and Ketones
Sec 1
Classification & Nomenclature
Sec 2 Structure Sec 3 Properties
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Sec 1 Classification & Nomenclature
OH O + H or OH A gem R C R'(H) O H R C R'(H) + 2 diol OH
The reaction is reversible, and a gem diol can eliminate water to regenerate a ketone or aldehyde.
O-CH3 C—H O-CH3 + H2O
The reaction of ketone with alcohol is slower than aldehyde’s, but cyclic acetal is easily formed.
CH3
dry HCl CH3 O HO An cyclic C O+ C acetal CH3 HO CH3 O Ethylene glycol Acetone ethylene ketal
(H)
(3) The aldehyde H will be lost easily
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Ⅰ. Nucleophilic Addition (亲核加成)
The most common reaction of aldehydes and ketones is the nucleophilic addition reaction, in which a nucleophile (:Nu or :Nu-) adds to the electrophilic carbon of the carbonyl group.
O CH3CH2CH2CCH3 O CH2=CHCCH2CH2CH3
5
4
2 1
1
3
6
2-Pentanone 2-戊酮
O CH3 C O CH2 C CH3
1-Hexen-3-one 1-己烯-3-酮
2,4-Pentanedione 2,4-戊二酮
5
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(2) Cyclic ketones are named with the carbonyl group occupying the 1-position in the ring.
O R—C—H
+ 2 HO—R’
dry HCl
OR' H R C
+ H2O
OR'
1,1-Dialkoxyalkane (Acetal, 缩醛)
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O CH3C－H ＋EtOH
Acetaldehyde
OH
dry HCl
CH3－C－OEt
EtOH
OEt CH3－C－OEt
CHO
CHO
1 2 3
Benzenecarbaldehyde Benzaldehyde 苯甲醛
4
4-Bromobenzaldehyde (p-Bromobenzaldehyde)
Br
2. Ketones
(1) In the IUPAC system, ketones are named by identifying the longest chain containing the carbonyl group and replacing the ‘ –e ’ with ‘–one.
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R
)
>
CH3 C=O R
13
2. React with sodium bisulphite (NaHSO3)
O R —C — H
+
OH :S—O- Na+ O
ONa R — C—H SO3H
OH R—C—H SO3Na
α-Hydroxysodium sulfonate α-羟基磺酸钠
H HO-CH2-CH2-CH2-C=O

OH
H 89%
H HO-CH2-CH2-CH2-CH2-C=O

OH
H 94%
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4. React with H2O: Hydration
Aldehydes and ketones undergo nucleophilic addition with water to yield 1,1-diols, or geminal (gem) diols.
H Acetaldehyde ethyl hemiacetal
H HOH Acetaldehyde diethyl acetal
O C—H + CH3OH NO2
H2SO4
(trace) NO2 76~65% 3-Nitrobenzaldehyde dimethyl acetal
3-硝基苯甲醛二甲基缩醛
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Mechanism of Nucleophilic Addition
Nu：
(—）
slow

H+
Nu
H
Nu
fast
Step 1 is the slowest, so this reaction is called as nucleophilic addition.