Ch16 Aldehyde Keton
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Transcript of Ch16 Aldehyde Keton
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Created byProfessor William Tam & Dr. Phillis Chang
Ch. 16 - 1
Chapter 16
Aldehydes & Ketones:Nucleophilic Additionto the Carbonyl Group
Ch. 16 - 2
About The Authors
These PowerPoint Lecture Slides were created and prepared by ProfessorWilliam Tam and his wife, Dr. Phillis Chang.
Professor William Tam received his B.Sc. at the University of Hong Kong in1990 and his Ph.D. at the University of Toronto (Canada) in 1995. He was anNSERC postdoctoral fellow at the Imperial College (UK) and at HarvardUniversity (USA). He joined the Department of Chemistry at the University ofGuelph (Ontario, Canada) in 1998 and is currently a Full Professor and
Associate Chair in the department. Professor Tam has received several awardsin research and teaching, and according to Essential Science Indicators , he iscurrently ranked as the Top 1% most cited Chemists worldwide. He haspublished four books and over 80 scientific papers in top international journalssuch as J. Am. Chem. Soc., Angew. Chem., Org. Lett., and J. Org. Chem.
Dr. Phillis Chang received her B.Sc. at New York University (USA) in 1994, herM.Sc. and Ph.D. in 1997 and 2001 at the University of Guelph (Canada). Shelives in Guelph with her husband, William, and their son, Matthew.
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Ch. 16 - 3
1. Introduction
Carbonyl compounds
O
R R'ketone
O
R Haldehyde
O
R OR'ester
(R, R' = alkyl, alkenyl, alkynyl or
aryl groups)
Ch. 16 - 4
2. Nomenclature of Aldehydes &Ketones
Rules● Aldehyde as parent (suffix)
Ending with “ al”;● Ketone as parent (suffix)
Ending with “ one ”● Number the longest carbon chain
containing the carbonyl carbon andstarting at the carbonyl carbon
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Ch. 16 - 5
ExamplesCl
H
O4-Chloro-2,2-dimethylpentan al
12345
O
Br
1
2 3 4 5 6
7
6-Bromo-4-ethyl-3-heptan one
Ch. 16 - 6
group as a prefix: methanoylor formyl group
O
H
group as a prefix: ethanoyl or
acetyl group (Ac)
O
groups as a prefix: alkanoyl or
acyl groups
O
R
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Ch. 16 - 7
2-Methanoyl benzoic acid(o- formyl benzoic acid)
CO2H
H
O
4-Ethanoylbenzenesulfonic acid( p- acetyl benzenesulfonic acid)
SO3H
O
Ch. 16 - 8
3. Physical Properties
Butane
bp -0.5 oC
(MW = 58)
H
O O
OH
Propanal
bp 49 oC
(MW = 58)
Butane
bp 56.1 oC
(MW = 58)
1-Propanol
bp 97.2 oC
(MW = 60)
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Ch. 16 - 9
4. Synthesis of Aldehydes
4A. Aldehydes by Oxidation of 1o
Alcohols
R OHR H
OPCC
Ch. 16 - 10
OH O
H
PCC
CH2Cl2(90%)
PCC
CH2Cl2
OH O
H(89%)
e.g.
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Ch. 16 - 11
4B. Aldehydes by Ozonolysis of Alkenes
R'
R
H
R"
OR'
R O
H
R"1. O 3
2. Me 2S+
Ch. 16 - 12
O
OH
1. O 3, CH2Cl2, -78oC
2. Me 2S
+
e.g.
H3C
1. O 3, CH2Cl2, -78oC
2. Me 2S
O
H3C
H
+O
H H
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Ch. 16 - 13
4C. Aldehydes by Reduction of AcylChlorides, Esters, and Nitriles
LiAlH4R OH
O
R HLiAlH4
O
R OH
O
R OR'
O
R Cl
R C N
or
or
or
Ch. 16 - 14
LiAlH4 is a very powerful reducing
agent, and aldehydes are easilyreduced
● Usually reduced all the way to thecorresponding 1 o alcohol
● Difficult to stop at the aldehydestage
Not a good method tosynthesize aldehydes usingLiAlH4
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Ch. 16 - 15
Two derivatives of aluminum hydridethat are less reactive than LAH
Lithium tri- tert -butoxy
aluminum hydride
AlR
OtBu
AlLi+ H OtBu
OtBu
Diisobutylaluminum hydride
(abbreviated i- Bu2 AlH or DIBAL-H)
Ch. 16 - 16
1. LiAlH(OtBu)3, -78oC
2. H 2O
O
R Cl
O
R OR'
R C N
O
R H
1. DIBAL-H, hexane, -78 oC
2. H 2O
1. DIBAL-H, hexane
2. H 2O
Acyl chloride
Ester
Nitrile
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Ch. 16 - 17
Aldehydes from acyl chlorides: RCOCl RCHO
1.
2.
O
R Cl
O
R OH
O
R H
SOCl2
LiAlH(OtBu)3,
Et2O, -78oC
H2O
e.g.
1. LiAlH(OtBu)3, Et 2O, -78oC
2. H 2O
Cl
O
CH3
H
O
CH3
Ch. 16 - 18
Reduction of an Acyl Chloride to an Aldehyde
LiAlH(O tBu)3R C
Cl
O
R CCl
O Li+ Al(O tBu)3
H
R C
Cl
O
H
Li
Al(OtBu)3R C
Cl
O
H
Al(OtBu)3
Li
R CH
O Al(OtBu)3-LiCl
R CH
OH2O
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Ch. 16 - 19
Aldehydes from esters and nitriles :RCO 2R’ RCHORC≡ N RCHO
● Both esters and nitriles can bereduced to aldehydes by DIBAL-H
Ch. 16 - 20
Reduction of an ester to an aldehyde
R COR'
O
H
Al(i -Bu)2 R COR'
O Al(i -Bu)2
H
R C
OR'
OH
Al(i -Bu)2R C
H
O H2O
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Ch. 16 - 21
Reduction of a nitrile to an aldehyde
R C N
H
Al(i -Bu)2 Al(i -Bu)2
H
NCR
R CN
H
Al(i -Bu)2R C
H
O H2O
Ch. 16 - 22
Examples
1. DIBAL-H, hexane, -78 oC
2. H 2O(1)
O
O
OH
H
O
1. DIBAL-H, hexane, -78 oC
2. H 2O
(2) C
H
O
N
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Ch. 16 - 25
Ketones from arenes by Friedel–Craftsacylations
O
R Cl
AlCl3 R
O
+ HCl+
an alkyl aryl
ketone
Ch. 16 - 26
Ketones from secondary alcohols byoxidation
OH
R R'
O
R R'
H2CrO4
or PCC
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Ch. 16 - 27
5B. Ketones from Nitriles
R C N1. R' M, Et2O
N M
R'R
2. H 3O+
O
R'R
Ch. 16 - 28
Examples
C N
O
Me1. MeLi, Et2O
2. H 3O+
C N1. , Et 2O2. H 3O
+MgBr
O
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Ch. 16 - 29
Suggest synthesis of
O
from andBr
HO
Ch. 16 - 30
Retrosynthetic analysis
O
HO
need to addone carbon
5 carbons here 4 carbons here
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Ch. 16 - 33
Suggest synthesis of
O
from andBr
HO
Ch. 16 - 34
Retrosynthetic analysis
O
HO
no need toadd carbon
5 carbons here
5 carbons here
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Ch. 16 - 35
Retrosynthetic analysis
O
MgBr
+H
O
HO
disconnection
Ch. 16 - 36
Synthesis
O
PCC
2. H 3O+
1. , Et 2O
MgBr
HO O
OH
PCC
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Ch. 16 - 37
6. Nucleophilic Addition to the
Carbon–Oxygen Double BondStructureO
C
~ 120 o
~ 120 o
~ 120 o
● Carbonyl carbon: sp 2 hybridized● Trigonal planar structure
Nu⊖
Ch. 16 - 38
Polarization and resonance structure
C
O O
C
● Nucleophiles will attack thenucleophilic carbonyl carbon
● Note: nucleophiles usually do notattack non-polarized C=C bond
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Ch. 16 - 39
With a strong nucleophile:
C OR
R'Nu: C O:
R
R'
Nu
H Nu
C O
R
R'
Nu
HNu: +
Ch. 16 - 40
Also would expect nucleophilic additionreactions of carbonyl compounds to becatalyzed by acid (or Lewis acid)
O
C H+
O
C
HO
C
H
(protonated carbonyl group)
+
● Note: full positive charge on thecarbonyl carbon in one of theresonance forms
Nucleophiles readily attack
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Ch. 16 - 41
+ A:C OHR
R'
C OHR
R'
Mechanism
C OR
R'H A +
(or a Lewis acid)
Ch. 16 - 42
+ A:C O
R
R'
NuH
H
C OHR
R':Nu H
Mechanism
C O
R
R'
:NuH
H A +
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Ch. 16 - 43
6A. Reversibility of Nucleophilic Additions to the Carbon – OxygenDouble Bond
Many nucleophilic additions to carbon–oxygen double bonds are reversible;the overall results of these reactionsdepend, therefore, on the position ofan equilibrium
Ch. 16 - 44
6B. Relative Reactivity: Aldehydesvs. Ketones
O
R H
O
R R'
O
R OR'> >
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Ch. 16 - 45
large
small
O
R H
O
R Nu
H
Nu
O
R R'
O
R
Nu
R'
Nu
Steric factors
Ch. 16 - 46
O
CR H
O
CR R' > >< <
Electronic factors
(positive inductiveeffect from onlyone R group)
(positive inductive effect fromboth R & R' groups) carbonylcarbon less + (lessnucleophilic)
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Ch. 16 - 47
7. The Addition of Alcohols:
Hemiacetals and Acetals Acetal & Ketal Formation: Addition of Alcohols to Aldehydes
R R'
O
R R'
R"O OHH+
R R'
R"O OR"
+ R"OH
H+
R"OH
hemi-acetal(R' = H)hemi-ketal(R' = alkyl)
acetal (R' = H)ketal (R' = alkyl)
Catalyzed
by acid
Ch. 16 - 48
O
CR R'
H+
+ R"OH
Mechanism
R C
R'
O:H
OR"
H+
R C
R'
O H
+ R"OH
OH
R O
R' R"
H
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Ch. 16 - 49
Mechanism (Cont’d)
OH
R O
R' R"
H R"OHOH
R OR"
R'R"
OH
H
hemi-acetal (R' = H) or
hemi-ketal (R' = alkyl)
+
OH2
R OR"
R'R C
R'
O
R"
H2O +
Ch. 16 - 50
R C
R'
OR"
R"OH
Mechanism (Cont’d)
OR"
R O
R' R"
H
R"OH
OR"
R OR"
R'
acetal (R' = H) orketal (R' = alkyl)
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Ch. 16 - 51
Note: All steps are reversible. In thepresence of a large excess ofanhydrous alcohol and catalyticamount of acid, the equilibriumstrongly favors the formation of acetal(from aldehyde) or ketal (from ketone)On the other hand, in the presence ofa large excess of H 2O and a catalyticamount of acid, acetal or ketal willhydrolyze back to aldehyde or ketone.This process is called hydrolysis
Ch. 16 - 52
Acetals and ketals are stable in neutralor basic solution, but are readilyhydrolyzed in aqueous acid
H+OR"
R OR"
R'
H2OO
R R'+ + 2 R"OH
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Ch. 16 - 53
Aldehyde hydrates: gem-diols
H2O+OH
H3C
H
H3C O
O
H
H
Acetaldehyde Hydrate(a gem -diol)
Ch. 16 - 54
C OH
H3C OH2
Mechanism
OH2H3C
O:H
OHH3C
OHH
OHHO
HR
O
R H+ H 2Odistillation
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Ch. 16 - 55
HO
OO
O
O
OH
H
Butanal-4-ol
A cyclichemiacetal
Hemiacetal: OH & OR groupsbonded to the same carbon
7A. Hemiacetals
Ch. 16 - 56
(+)-Glucose(A cyclic hemiacetal)
OHO
HO OHOH
OH Hemiacetal: OH & ORgroups bonded to thesame carbon
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Ch. 16 - 57
Sucrose(table sugar)
O
O
OHO
OH
HOHO
OHHO
OH
OH An acetal
A ketal
7B. Acetals
Ch. 16 - 58
+O
R R'
HOOH
H3O+
O O
R R'
+ H2O
Ketone (excess) Cyclic acetal
Cyclic acetal formation is favored whena ketone or an aldehyde is treated withan excess of a 1,2-diol and a trace ofacid
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Ch. 16 - 59
+
O
R R'
HOOH
H3O+
O O
R R'
+ H2O
This reaction, too, can be reversed bytreating the acetal with aqueous acid
Ch. 16 - 60
7C. Acetals Are Used as Protecting Groups Although acetals are hydrolyzed toaldehydes and ketones in aqueous acid,acetals are stable in basic solutions
R'O OR"
R H H2O
OHNo Reaction
O O
R R'H2O
OHNo Reaction
Acetals are used to protect aldehydes andketones from undesired reactions in basicsolutions
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Ch. 16 - 61
O
OH
Br
O
Attempt tosynthesize:
from:
Example
Ch. 16 - 62
O
O
OH
BrMg
O
+
● Synthetic plan
This route will not work
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Ch. 16 - 63
BrMg
O
Reason:(a) Intramolecular nucleophilic addition
(b) Homodimerization or polymerization
BrMg
O
BrMg
O
BrMg
O
Ch. 16 - 64
Br
O O
HOThus, need to “protect” carbonyl group first
Br
O O
HOOH
, H+
(ketal)
BrMg
O O
MgEt2O
O
OMgBr
O O
aqueous H +
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Ch. 16 - 65
7D. Thioacetals
Aldehydes & ketones react with thiolsto form thioacetalsEtS SEt
R H
O
R H
2 EtSH
HA + H2O
Thioacetal
O
R R' BF3 + H2O
S S
R R'
HSSH
Cyclicthioacetal
Ch. 16 - 66
Thioacetal formation with subsequent “desulfurization” with hydrogen andRaney nickel gives us an additionalmethod for converting carbonyl groupsof aldehydes and ketones to –CH 2 –groups
H2, Raney Ni
+ NiS
S S
R R'HS SH
R R'
H H+
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Ch. 16 - 67
8. The Addition of Primary and
Secondary Amines Aldehydes & ketones react with 1 o amines to form imines and with 2 o amines to form enamines
From a 1 o amine From a 2 o amine
N
R 1 R 2
R 3
Imine
R 1
NR 5
R 2
R 3
R 4
Enamine
R 1, R 2, R 3 = C or H;R 4, R 5 = C
Ch. 16 - 68
8A. Imines
Addition of 1 o amines to aldehydes &ketones
R
R'O H2N R"
R
R'N
R"
H++
(1o amines) (imines)
[(E ) & ( Z ) isomers]
+ H2O
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Ch. 16 - 69
H2NR"
Mechanism
R R'
O H3O+
R R'
OH O
R R'
H
N R"
H
H
-H+
O
R R'
H
NHR"
(amino alcohol)
H+OH2
R R'
NHR"NR'
R
R"
H
H2O
NR'
R
R"
Ch. 16 - 70
Similar to the formation of acetals andketals, all the steps in the formation ofimine are reversible. Using a largeexcess of the amine will drive theequilibrium to the imine sideHydrolysis of imines is also possible byadding excess water in the presence ofcatalytic amount of acid
NR'
R
R"H2O
H+O
R'
R + + H2NR"
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Ch. 16 - 71
8B. Oximes and Hydrazones
Imine formation – reaction with a 1o
amineC O H2N R C N+
R + H2O
a 1 o amine an imine[(E ) & ( Z ) isomers]
aldehydeor ketone
C O H2N OH C N+
OH
+ H2O
hydroxylamine
an oxime[(E ) & ( Z ) isomers]
aldehydeor ketone
Oxime formation – reaction withhydroxylamine
Ch. 16 - 72
Hydrazone formation – reaction withhydrazine
C O H2NNH2 C N+NH2
+ H2O
hydrazine a hydrazonealdehydeor ketone
N R C C+N
+ H2O
2o amine
cat. HA O
CC
H R
H
R R
enamine
Enamine formation – reaction with a 2 o amine
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Ch. 16 - 73
8C. Enamines
N R 5+
N
+ H2O
2o amine
cat. HA O
C R 3
R 2H
R 1
R 4H
R 4 R 5
enamine
R 3R 1
R 2
Ch. 16 - 74
N R +
O
CC
H R
H
Mechanism
C C
H
O
N
R
R
H
aminoalcoholintermediate
C C
H
O
N R
R
H
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Ch. 16 - 75
C C
H
O
N R
R
H
A H +
Mechanism (Cont’d)
C C
H
O
N R
R
HH
iminium ionintermediate
C
H
CN
R
R :A + H 2O +
Ch. 16 - 76
C
H
CN
R
R
A:
Mechanism (Cont’d)
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Ch. 16 - 77
9. The Addition of Hydrogen
Cyanide: Cyanohydrins Addition of HCN to aldehydes & ketones
R R'
OHCN
OH
R R'
CN
O
R R'
CNH+
CN
(cyanohydrin)
Ch. 16 - 78
R R'
O CN
Mechanism
O
R R'
CN(slow)
NC H
OH
R R'
CN
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Ch. 16 - 79
Slow reaction using HCN since HCN is aweak acid and a poor source ofnucleophileCan accelerate reaction by using NaCNor KCN and slow addition of H 2SO4
R R'
O
NaCN
O Na
R
CN
R'
OH
R
R'
CNH2SO4
Ch. 16 - 80
R'
OHCN
R R'
R HO CN
R'R
COOH95% H 2SO4
heat
HCl, H2O
heat R'R
HO COOH
1. LiAlH4
2. H 2O R'R
HO NH2
( -hydroxy acid)
( , -unsaturated acid)
( -aminoalcohol)
Synthetic applications
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Ch. 16 - 81
10. The Addition of Ylides: The
Wittig ReactionR
R'O
aldehydeor ketone
+ (C6 H5 )3 P CR"
R"
C CR'
R
R"
R"
O P(C6 H5 )3+
phosphorus ylide(or phosphorane)
alkene[(E) & (Z) isomers]
triphenyl-phosphine
oxide
Ch. 16 - 82
Phosphorus ylides
(C6H5)3P CR"
R"(C6H5)3P C
R"
R"
(C6H5)3P CHR"'
R"(C6H5)3P: XXCH
R"'
R"+
triphenyl-phosphine
an alkyltriphenylphos-phonium halide
(C6H5)3P C
R"'
R"
H :B + H:B(C6H5)3P CR"'
R"
a phosphorusylide
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Ch. 16 - 83
Example
(C6H5)3P CH3(C6H5)3P: Br+
Methyltriphenylphos-phonium bromide
(89%)
CH3Br C6H6
(C6H5)3P CH3
Br
+ C6H5Li (C6H5)3P CH2:
+ + LiBrC6H6
Ch. 16 - 84
Mechanism of the Wittig reaction
+C
O
R R'R"
:C R"'
P(C6H5)3: :
aldehydeor ketone
ylide
R'
C CR
:O
R"
R"'
P(C6H5)3
oxaphosphetane
:
C CR
R'
R"
R"O P(C6H5)3 +
alkene(+ diastereomer)
triphenylphosphineoxide
: :
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Ch. 16 - 85
10A. How to Plan a Witting Synthesis
Synthesis of
using a Wittig reaction
Ch. 16 - 86
Retrosynthetic analysis
disconnection
O
Ph3P+route 1
BrPh3P: +route 2
PPh3
O+
Br
+ :PPh 3
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Ch. 16 - 87
Synthesis – Route 1
O
Ph3PBr:PPh 3
Br
nBuLi
Ph3P
Ch. 16 - 88
Synthesis – Route 2
PPh3 Br
O
:PPh 3
nBuLi
Br
PPh3
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Ch. 16 - 89
10B. The Horner – Wadsworth – EmmonsReaction
P OEt
O
OEt
NaH
+ H 2
P OEt
O
OEt
a phosphonateester
Ch. 16 - 90
+P OEt
O
OEt
H
O
EtO P O
O
EtONa+
84%
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Ch. 16 - 91
P OEtO
OEt
X
OEt
PEtO OEt
+
EtX +
Triethyl phosphite
The phosphonate ester is prepared byreaction of a trialkyl phosphite [(RO) 3P]with an appropriate halide (a processcalled the Arbuzov reaction)
Ch. 16 - 92
11. Oxidation of Aldehydes
R H
O O
R O
O
R OH
H3O+
KMnO4, OH
or Ag 2O, OH
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Ch. 16 - 93
12. Chemical Analyses for Aldehydesand Ketones
R
R'O + NO2
O2N
N
H
H2N
R
R'
N
NH
NO2
O2N
H
hydrazine
hydrazone(orange ppt.)
12A. Derivatives of Aldehydes & Ketones
Ch. 16 - 94
R H
O O
R O
Ag(NH3)2
H2O+ Ag
silvermirror
12B. Tollens ’ Test (Silver Mirror Test)
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Ch. 16 - 95
13. Spectroscopic Properties of
Aldehydes and Ketones13A. IR Spectra of Aldehydes and Ketones
Range (cm )
R CHO Ar CHO
C CCHO
C CCOR
RCOR ArCOR
Compound Range (cm )Compound
Cyclohexanone
Cyclopentanone
Cyclobutanone
1715
1751
1785
1720 - 17401695 - 1715
1680 - 1690
1705 - 17201680 - 1700
1665 - 1680
C=O Stretching Frequencies
Ch. 16 - 96
Conjugation of the carbonyl group witha double bond or a benzene ring shiftsthe C=O absorption to lowerfrequencies by about 40 cm -1
O Osingle bond
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Ch. 16 - 97
Ch. 16 - 98
13B. NMR Spectra of Aldehydes andKetones
13C NMR spectra● The carbonyl carbon of an aldehyde
or ketone gives characteristic NMRsignals in the 180–220 ppm region of 13C spectra
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Ch. 16 - 99
1H NMR spectra● An aldehyde proton gives a distinct 1H
NMR signal downfield in the 9–12 ppm region where almost no other protonsabsorb; therefore, it is easily identified
● Protons on the carbon are deshieldedby the carbonyl group, and their signalsgenerally appear in the 2.0–2.3 ppm region
● Methyl ketones show a characteristic(3H) singlet near 2.1 ppm
Ch. 16 - 100
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Ch. 16 - 101
Ch. 16 - 102
14. Summary of Aldehyde andKetone Addition Reactions
O
OH
R 1. RM
2. H 3O+
OH
H1. LiAlH4 or NaBH 4
2. H 3O+
OH
CN
1. NaCN
2. H 3O+
R R PPh3
RO OR
2 ROH, H +
NR
R-NH2, H+
R 2NH
H+
NR 2
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Ch. 16 - 103
END OF CHAPTER 16