alkenes and alkynes (ii) 9.1 introduction: additions to alkenes we shall study other examples of...
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Alkenes and alkynes (II)
9.1 Introduction: Additions to alkenes
We shall study other examples of additions to the double bonds of alkenes. We begin with the additions of hydrogen halides, sulfuric
acid, water (in the presence of an acid catalyst), and halogens.
C C + A-B A C C BAddition
An Addition reaction
C C
H C C X
Alkene
H X
HOSO2OHH C C OSO2OH
H C C OH
HOH
Alkyl halide
Alkyl hydrogen sulfate
Alcohol
X C C X
X - X
Dihaloalkane
1. An addition reaction results in the conversion of one pi π -bond
and one sigma-bond into two sigma bonds
C C X C C YX - Y+
Bonds broken
2 - Bonds formed
sp2
sp3
Addition
2. The electrons of the pi-bond are exposed. Because the pi-
bond results from overlapping p orbital, the pi electrons lie above
and below the plane of the double bond:
C C
sp2
Electrophiles Ç×µçÊÔ¼Á
H+, X+,Lewis acids; BF3 and AlCl3Metal ions; Ag+, Hg2+, Pt2+,
Love elctrons
Hydrogen halides react with alkenes
H+ Cl-
Carbocation (Õý̼Àë×Ó£©
H + Cl- H Cl
Slow fast
C CC C
H
Cl
sp2
sp3
H+ Cl-H
+ Cl-
slow fast
Addition Reaction Mechanism
Carbocation (Õý̼Àë×Ó£©
9.2 Addition of Hydrogen Halides to Alkenes: Markovnikov’
s Rule ( 马氏规则)
What is it Mar’s Rule?-----The addition of HX to an alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms.
H2C CHCH3 + H+X- CH2CHCH3
H X
Markovnikov addition productCarbon atom with the greater number of hydrogen atoms
Markovnikov’s Rule ( 马氏规则)
H2C CCH3 + HCl CH2C(CH3)2
H Cl
(not ClCH2CH(CH3)2
CH3
tert-Butyl chloride2-Methylpropene
CH3
+ HCl
Cl
CH3
H
Methylcyclohexene 1-Chloro-1-Methylcyclohexane
A mechanism for addition of a hydrogen halide to an alkene
(two steps;)
Step 1 + HXSlow
H
+
rate-determining step
Step 2
H
+ + X-fast
H X
9.2A Theoretical explanation of Markovnikov’s Rule
CH
CH2 + H-Br CH3CHCH2H
Br
Markovnikov addition product
(not BrCH2CHCH3)H3C
H
Methyl push electron
1. Electronic Effects ( 电子效应)
H2C C + HCl CH2C(CH3)2
H Cl
(not ClCH2CH(CH3)2
CH3
tert-Butyl chloride2-Methylpropene
CH3
CH3
+ HCl
Cl
CH3
H
Methylcyclohexene 1-Chloro-1-Methylcyclohexane
2. The Stabilities of carbocation
(碳阳离子的稳定性解释马氏规则)
CH
CH2 + H-Cl
CH3CHCH2H
Markovnikov addition product
H3C
+b
a
CH3CHCH2
+
Cl-CH3CHClCH3
2o C+
Cl-CH3CH2CH2Cl
Anti-Mar's Rule1o C+
Stable
Unstable
2o C+ 1o C+
a
bH
The Stabilities of carbocation
C CH2+ H-Cl
CH3CCH2H
Markovnikov addition product
H3C
+b
a
CH3CCH2
+
Cl-CH3CClCH3
3o C+
Cl-CH3CHCH2Cl
Anti-Mar's Rule
1o C+
Stable
Unstable
3o C+ 1o C+
a
bH
CH3
CH3
CH3
CH3
CH3
Mar’s Rule help us to predict the outcome of the addition
reactionH2C C + HCl CH2C(CH3)2
H Cl
(not ClCH2CH(CH3)2
CH3
tert-Butyl chloride2-Methylpropene
CH3
Major Product
H2C C + I-Cl CH2C(CH3)2
I Cl
(not ClCH2CI(CH3)2
CH3
2-Chloro-1-iodo-2-methylpropane2-Methylpropene
CH3
(Major product)
9.2D An exception to Markovnikov’s Rule
( 马氏规则例外)The addition of HBr to alkenes, it is Only when HBr is used in the presence of peroxides (ROOR), it is an exception to Mar’ R
ule.
CH3CH=CH2 + HBr
ROORCH3CH2CH2Br
Major product
CH3CHBrCH3
Mar's product
Ionic reaction
Free radical reaction
9.3 Stereochemistry of the Ionic Addition to an alkene
CH3CH2CH=CH2 + HCl CH3CH2CHCH3*
Cl
(± )-2-Chlorobutane
We got a racemic form? Do you know why?
CH3CH2CH=CH2 + HCl CH3CH2CHCH3*
Cl
(± )-2-Chlorobutane
H+
CH2H
C+
H CH2CH3
Cl-H3C
Cl
H3CH2C
HCl-
CH3
ClH
CH2CH3
Achiral, trigonalPlanar carbocation( S )-2-Chlorobutane
(50%)( R )-2-Chlorobutane (50%)
Enantiomers
A recemic form (ÍâÏûÐýÌ壩
9.4 Addition of sulfuric acid to alkenes
+ HO S OH
O
O
C C
H
+
Step 1, The alkene accepts a proton (H+) from sulfuric acid to form a carbocation
CarbocationSulfuric acid
Slow
Alkene
C C
H
+
Carbocation
+ -O S OH
O
O
Hydrogen Sulfate ionÁòËáÇâ¸ù¸ºÀë×Ó
C C
H
OSO2OH
Alkyl hydrogen sulfateÍé»ùÇâÁòËáõ¥
fast
Step 2, The carbocation reacts with a hrdrogen sulfate ion to form an alkyl hydrogen sulfate
The addition of sulfuric acid is also regioselective ( 区域选择
性)
+ HO S OH
O
O
Sulfuric acidPropene
CH3CH=CH2
CH3CHCH2+
CH3CH2CH2+
Mar's addition
Anti Mar's addition
More Stablecarbocation
Less Stablecarbocation
HOSO2O-
CH3CHCH3
OSO2OH
Isopropyl hydrogen sulfate ÁòËáÇâÒì±ûõ¥
HOSO2O-
CH3CH2CH2OSO3H
Propyl hydrogen sulfate ÁòËáÇâÕý±ûõ¥
9.4A Alcohol from alkyl hydrogen sulfates
( 从硫酸氢乙酯制醇)Alkyl hydrogen sulfates can be easily
hydrolyzed to alcohols by heating them with water
+ HO S OH
O
O
Sulfuric acidPropene
CH3CH=CH2 CH3CHCH2+Mar's addition
More Stablecarbocation
HOSO2O-
CH3CHCH3
OSO2OH
Isopropyl hydrogen sulfate ÁòËáÇâÒì±ûõ¥H2O
Heat
CH3CHCH3
OH
+ H2SO4
Isopropanol
9.5 Addition of water to alkenes: Acid-catalyzed
hydrationThe acid-catalyzed addition of water to the double bond of an alkene is a method for the preparation of low molecular weight alc
oholsC C
Alkene
+
Water
C C
OH
H
Alcohol
HOHH+
Hydration (証죩
This reaction is followed Markovnikov's addition Rule
An example is the hydration of 2-methylpropene
C C
2-Methylpropene(Isobutylene)
+
Water
H3C C
CH3
C
H
OHH
H
tert-Butyl alcohol
H3C H
HH3C
HOHH+
Hydration (証죩
This reaction is also followed Markovnikov's addition Rule
Mechanism for the hydration of 2-methylpropene
C C
2-Methylpropene(Isobutylene)
+ H3C C
CH3
C
H
H
HH3C H
HH3C
HOHH+
Hydration (証죩 H
+
Step 1.
+ H2O
Carbocation
Slow
+
Step 2. H3C C
CH3
C
H
H
H
++ H2O:
Carbocation
H3C C
CH3
C
H
H
H
O+ H
H
fast
H3C C
CH3
C
H
H
H
O+ H
H
Step 3. +H2O:
fast
H3C C
CH3
CH3
O H
+ H3O+
tert-Butyl alcohol
Alkenes hydration is followed the occurrence of rearrangements
CH
CH2
3,3-Dimthyl-2-butene
+ H3C C
CH3
CHHOHH2SO4
Hydration (証죩 H
2o Carbocation
Slow
+C
CH3
CH3
H3C
CH3
+CH3
H3C C
CH3
C
3o Carbocation
CH3
CH3
+
H
H3C C
CH3
C CH3
CH3+
H
H2O:
OH2
-H+
H3C C
CH3
C CH3
CH3
H
OH
2,3-Dimethyl-2-butanol(Major product)
-CH3 immagration
9.6 Addition of bromine and chlorine to alkenes
1. Alkanes react with bromine
R H + Br2
Room temp
in the dark, CCl4
No appreciable reaction
Alkane
R H + Br2
Room temp
sunlight, CCl4Alkane
R Br + HBr
Alkyl halide Hydrogen bromide(detected by moist blue litmus)
(red brown)(Colorless)
2. Addition of bromine and chlorine to alkenes
+ Br2
Room temp
in the dark, CCl4
Alkene (red brown) Br Br
Vic-Dibromide(ÁÚ-¶þä廯Î (colorless)
Because of rapid decolorization of Br2/CCl4, it is a useful test for carbon-carbon multiple bonds (¼ìÑéÖؼü£©
Distinguish alkanes with alkenes (区别烷烃和烯烃)
+ Br2
Room temp
in the dark, CCl4
Alkene (red brown)
CH2=CH2 CH2BrCH2Br
1,2-Dibromoethane
(Colorless)
CH3CH3 Br2
Room temp
in the dark, CCl4
(red brown)
+ No reaction
Alkane
Distinguish cycloalkanes with cycloalkenes (区别环烷烃和环烯
烃)
+ Br2
in the dark, CCl4
cyclohexene (red brown)
Br2
Room temp
in the dark, CCl4
(red brown)
+ No reaction
trans-1,2-Dibromocyclohexane
cyclohexane
(Colorless)
Br
Br
H
H
3. Addition reaction of chlorine to alkenes
+ Cl2
2-butene2,3-Dichlorobutane
(Colorless)
CH3CH=CHCH3 CH3CHClCHClCH3-9oC
CH3CH2CH=CH2 + Cl2-9oC 1,2-Dichloropentane
(Colorless)
CH3CH2CHClCH2Cl
1-Pentene
9.6A Mechanism of halogen addition
Electrophiles Ç×µçÊÔ¼Á+ Br Br
Br+
Bromonium ion(äåÎÌÀë×Ó£©
Br-
Br+
Br
BrBr
Br
+
trans-Dibromide trans-Dibromide
9.7 Stereochemistry of the addition of halogens to alkenes
It is anti addition ( 反式加成)
Br2
CCl4
Br
H
H
Br
cyclopentene trans-1,2-Dibromocyclopentane(E)-1,2-Dibromocyclopentane
This anti addition of bromine to cyclopentene can be explai
ned by a mechanism
Br2
CCl4
cyclopentene
BrH H
+
Br-
Bromonium ion
BrH
BrH
HBr
HBr
+
Enantiomer
trans-1,2-Dibromocyclopentane(E)-1,2-Dibromocyclopentane
9.7A Stereospecific reactions (立体专一性反应)
trans-2-Butene
Bromonium ion
H
H3C H
CH3
+ Br2
H3C
HCH3
HBr+
Br-
ab
(chiral ÊÖÐÔ·Ö×Ó£©
Br
Br
H3C
H
H
CH3
Br
Br
H
H3C CH3
H
a
b
(2R, 3S) (meso ÄÚÏûÐý£©
(2R, 3S) (meso ÄÚÏûÐý£©
£¨¶Ô³ÆÖÐÐÄ£©
£¨¶Ô³ÆÖÐÐÄ£©
trans-2-Butene reacts with bromine
Cis-2-Butene reacts with bromine
cis-2-Butene
Bromonium ion
H3C
H H
CH3
+ Br2
H
H3CCH3
HBr+
Br-
ab
(achiral ·ÇÊÖÐÔ·Ö×Ó£©
Br
Br
H
H3C
H
CH3
a
b
(2R, 3R) ( chiral ÊÖÐÔ·Ö×Ó£©£¨ÎÞ¶Ô³ÆÖÐÐÄ£©
Br
Br
H3C
H CH3
H
£¨ÎÞ¶Ô³ÆÖÐÐÄ£©Enantiomer (¶ÔÓ³Òì¹¹Ì壩
(2S, 3S) ( chiral ÊÖÐÔ·Ö×Ó£©
9.8 Halohydrin formation (卤代醇的形成)
If the halogenation of an alkene is carried out in aqueous solution (rather than in carbon tetrachloride), the major product of the overall reaction is not a vic-dihalide, but rather it is a
halo alcohol called a halohydrin.
+ X2 + H2OC
X
C
OH
+ C
X
C
X
Halohydrin vic-Dihalide
Major product Minor product
Halohydrin formation can be explained by the following mechan
ism:
+ X H2OX
+Step1.C C
X+
Halonium ion
Step2. C C
X+
Halonium ion
H2O X-
Anti-addition
C
X
C
OH
+ C
X
C
X
Halohydrin vic-Dihalide
Major product Minor product
Isobutene reacts with bromine in water
C CH2
H3C
H3C
Br2
CH3
CH3C CH2
Br+
:OH2
H3C
CH3
+OH2
CH2Br
- H+
H3C
CH3
OH
CH2Br
(73%)
9.9 Radical addition to alkenes: The anti-Markovnikov addition o
f hydrogen bromideR O O R
An organic peroxideÓлú¹ýÑõ»¯Îï
R O O H
An organic hydroperoxideÓлú¹ý Ñõ»¯Çâ
HC CH2
HBrH3C H3C CHCH3
Br
No peroxideÎÞ¹ýÑõ»¯Îï
Markovnikov addition·ûºÏÂí¶û¿Æ·òÄá¿Æ·ò¼Ó³É
HC CH2
HBrH3C H3C CH2CH2
Br organic peroxide Óлú¹ýÑõ»¯Îï
Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³ÉR O O R
Do you know why?
HC CH2
HBrH3C H3C CH2CH2
Br organic peroxide Óлú¹ýÑõ»¯Îï
Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³ÉR O O R
Do you know why?
It is a free radical reaction (×ÔÓÉ»ù·´Ó¦£©
HC CH2
HBrH3C H3C CHCH3
Br
No peroxideÎÞ¹ýÑõ»¯Îï
Markovnikov addition·ûºÏÂí¶û¿Æ·òÄá¿Æ·ò¼Ó³É
It is an ionic reaction £¨ Àë×Ó·´ Ó¦£©
Free Radical reaction
R O O R
An organic peroxideÓлú¹ýÑõ»¯Îï
Step 1.heat
2 R O
Chain Initiation
Step 2. R O + HBr ROOH + Br
HC CH2Br
H3C
Chain Propagation
CH3CHCH2BrStep 3.
H3C CHCH2
Br
Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³É
Step 4. CH3CHCH2Br H Br+
H
9.9A Other radical additions to alkenes
Tetrabromomethane (CBr4) reacts with 1-octene(1- 辛烯 )to yield 1,1,1,3-tetrabromonon
ane
CH3(CH2)5CH=CH2 + CBr3 CH3(CH2)5CHCH2CBr3
Br
1,1,1,3-tetrabromononane
(1,1,1,3-ËÄäåÐÁÍ飩
Br
Radical additions
ROOR
The mechanism for this reaction is as follows:
Chain Inition
Step 1 RO OR 2RO
RO + Br CBr3ROBr + CBr3Step 2
CH3(CH2)5CHCH2CBr3
Br
1,1,1,3-tetrabromononane
(1,1,1,3-ËÄäåÐÁÍ飩
Chain Propagation
Step 3 CH3(CH2)5CH=CH2 + CBr3 CH3(CH2)5CHCH2CBr3
Step 4 CH3(CH2)5CHCH2CBr3 Br CBr3+
Other examples of radical additions to alkenes are the
following:CH3(CH2)3CH=CH2 + HCCl3
ROOR
peroxideCH3CH2CH2CH2CH2CCl3
1,1,1-Trichlorohexane1-Hexene
(CH3)2C=CH2 + CH3CH2SHROOR
peroxide(CH3)2CHCH2SCH2CH3
Isobutene
CH3CH2C=CH2
CH3
+ CCl4 CH3CH2CCH2CCl3
CH3
Cl
1,1,1,3-Tetrachloro-3-methylpentane
peroxide
ROOR
Isopentene
9.10 Radical polymerization of alkenes ( 烯烃的自由基聚
合) :Addition polymers ( 加成聚合)
m CH2=CH2
EthyleneMonomer (µ¥Ì壩
Polymerization
ROOR* CH2CH2 *
n
Polyethylene (¾ÛÒÒÏ©£©polymer (¸ß·Ö×Ó»ò¾ÛºÏÎ
£¨m and n are large numbers)
m CH2=CH
Styrene (±½ÒÒÏ©£©Monomer (µ¥Ì壩
Polymerization
ROOR* CH2CH *
n
Polystyrene (¾Û±½ÒÒÏ©£©polymer (¸ß·Ö×Ó»ò¾ÛºÏÎ
£¨m and n are large numbers)
Other common addition polymers
m CH2=CH
Chloroethene (ÂÈÒÒÏ©£© (µ¥Ì壩
Polymerization
ROOR* CH2CH *
n
Poly(vinyl chloride) (¾ÛÂÈÒÒÏ©£©
Cl Cl
m CH2=CH
Acrylonitrile (±ûÏ©ë棩 (µ¥Ì壩
Polymerization
ROOR* CH2CH *
n
Polyacrylonitrile (¾Û±ûÏ©ë棩 Orlon °ÂÂÚ
CN CN
m CF2=CF2
Tetrafluoroethene (ËÄ·úÒÒÏ©£© (µ¥Ì壩
Polymerization
ROOR* CF2CF2 *
n
Polytetrafluoroethene (¾ÛËÄ·úÒÒÏ©£© £¨ËÜÁÏÍõ£©(Teflon)
m CH2=CCOOCH3
Methyl methacrylate (¼×»ù±ûÏ©Ëá¼×õ¥£© (µ¥Ì壩
Polymerization
ROOR* CH2C *
n
Poly(methyl methacrylate) (¾Û¼×»ù±ûÏ©Ëá¼×õ¥£© £¨Óлú²£Á§£©
CH3 CH3
COOCH3
9.11 Oxidations of alkenes ( 烯烃的氧化) : Syn hydroxyl
ation (顺式 - 羟基化作用)Alkenes undergo a number of reactions in which the carbon-carbon double bond is oxidized. Potassium permanganate (KMnO4) or osmiun tetroxide ( OsO4), for example, can be used to oxidize alkenes to 1,2-diols
(1,2- 二醇) called glycols (乙二醇) .C C
cold 5% KMnO4
or OsO4, Na2SO3OH OH
Syn-1,2-diols
C C
H
H
H
H
cold 5% KMnO4
or OsO4, Na2SO3
H
H
H
H
OH OH
1,2-Ethanediol(ethylene glycol)
Ethene
C C
H
H
H
H3C
cold 5% KMnO4
or OsO4, Na2SO3
H
H
H
H
OH OH
1,2-Propanediol(1,2-±û¶þ́ ¼£©(propylene glycol)
Propene
9.11A Syn hydroxylation of alkenes----Mechanism
C C
cold 5% KMnO4
O O
Mn
O O-
NaOH, H2O
Mn
O
O O
O-
Syn-1,2-diols
OH OH
OH-
H2O
C COsO4, Na2SO3
O O
Syn-1,2-diols
OH OH
Os
O O-
OH-
H2O
Os
O
O O
O
+ MnO4-
O
Mn
O
O O-
H H
H2O
OH-
OH OH
H H
cis-1,2-Cyclopentanediol(a meso compound)
Cold
+ OsO4
O
Os
O
O O
H H
NaHSO3
OH OH
H H
cis-1,2-Cyclopentanediol(a meso compound)
However, osmium tetroxide is highly toxic and is very expensive.
9.12 Oxidative cleavage of alkenes
Alkenes are oxidatively cleaved to salts of carboxylic acids by hot permanganate solu
tions.KMnO4
Acetic acid(ÒÒËᣩ
OH-, heatH3CHC CHCH3 2 CH3COOH
KMnO4
Acetic acid(ÒÒËᣩ
OH-, heatH3CC CHCH3 2 CH3COOH
CH3
CH3CCH3
O
+
acetone
CH3CH2C CH2
CH3
KMnO4
Carbon dioxide
OH-, heatCH3CH2CCH3
O
+
Butanone
O=C=O + H2O
An unknown alkene with the formula C7H12 undergoes oxidation by hot basic KMnO4 to yield, after acidifi
cation, only one product:
KMnO4, OH-, heat1,
2, H+C7H12 CH3CCH2CH2CH2CH2COOH
O
Unknown alkene(δ֪ϩÌþ)
CH3
1-Methylcyclohexene
9.12A Ozonolysis of alkenes ( 烯烃的臭 O3 氧化)
-O
O
O
O
O
O
Initial ozonideÒ»¼¶³ôÑõ»¯Îï
Second ozonide¶þ¼¶³ôÑõ»¯Îï
O
O O
Zn, H2OO O+
Aldehydes or ketones (È©»òͪ£©
reduction
The overall process of ozonolysis followed by reduction with zinc and water amounts to a disconnection of the carbon-carbon double bond
in the following fashion.
( 2 ) Zn, H2O reduction
R
R
R''
H
( 1 ) O3, CH2Cl2, -78oCR
R
O O
R''
H
+
Aldehydes (È©)
ketones (ͪ£©
( 2 ) Zn, H2O reduction
H3C
H3C
CH3
H
( 1 ) O3, CH2Cl2, -78oC
( 2 ) Zn, H2O reduction
CH
H
H
H
( 1 ) O3, CH2Cl2, -78oCH3C
CH3
H3C
H3C
O O
CH3
H
+
Acetaldehyde (ÒÒÈ©)
Acetone (±ûͪ£©
CH
H
O O
H
H
+
Formaldehyde (¼×È©)
Isobutylaldehyde (Ò춡ȩ£©
CH3
H3C
9.14 Addition of bromine and chlorine to alkynes
Br2, CCl4C C C C
Br
Br
Dibromoalkene
Br2, CCl4C C
Br
Br
Br
BrTetrabromoalkane
Cl2, CCl4C C C C
Cl
Cl
Dichloroalkene
Cl2, CCl4C C
Cl
Cl
Cl
ClTetrachloroalkane
It is usually possible to prepare a dihaloalkene by simply adding one molar equivalent of the halo
genBr2, (1 mol)
C C CH2OH C C
H3CH2CH2C
Br
Br
CH2OH
( 80%)
CH3CH2CH2
CCl4
HOOCC CCOOHBr2, (1mol)
C C
HOOC
Br
Br
COOH
( 70%)
CCl4Acetylenedicarboxylic acid(¶¡È²¶þËᣩ
trans or (E)-2,3-Dibromobutenedicarboxylic acid(2£¬3-¶þä嶡ϩ¶þËᣩ
9.15 Addition of hydrogen halides to alkynes ( 炔烃与卤化氢的
加成)C C C C
H
Cl
chloroalkene
HClHCl
follow Mar's RuleC C
H
H
Cl
Clgem-Dichloride
C C C C
H
Br
bromoalkene
HBrHBr
follow Mar's Rule
C C
H
H
Br
Brgem-Dibromide
C CHH3C C CH2
Cl
H3C
2-Chloropropene
HClHCl
follow Mar's Rule
H3C C C H
Cl
Cl
H
H
2,2-Dichloropropane
9.19 Simple chemical tests for alkanes, alkenes, alkynes, alkyl h
alides, and alcohols
9.19A Chemical tests
9.19B Concentrated sulfuric acid (H2SO4)
Alkenesalkynesalcohols H2SO4
AlkanesAlkyl halides
cold
Soluble in H2SO4
insoluble in H2SO4
9.19C Bromine in carbon tetrachloride ) (Br2/CCl4)
Alkenesalkynes
Br2 / CCl4
AlkanesAlkyl halidesalcohols
Decolorization of bromine
do not react with brominein the absence of light
9.19D Cold dilute potassium permanganate (KMnO4)
Alkenesalkynes
cold KMnO4
AlkanesAlkyl halidesalcohols
The deep-purple color of KMnO4 disappearto form MnO2
do not react with KMnO4
9.19E Alcoholic silver nitrate (AgNO3 / ROH)
AlkenesAlkynesAlcohols AgNO3Alkanes
ROHAlkyl halides
No reaction
AgX
9.19F Silver Nitrate in ammonia (AgNO3 / NH3)
AlkenesAlcohols
Ag(NH3)2+
Alkanes
OH-
Alkyl halides
AlkynesRC CH
No reaction
RC CAg
(terminal alkynes)
Special Topic C-----Divalent carbon compounds: Carbenes ( 卡宾 or
碳烯)
• Neutral divalent carbon compounds are called carbenes ( 卡宾 CH2: Methylene )
• Most carbenes are highly unstable compounds.• The reactions show a stereospecificity• The reactions of carbenes are also of great sy
nthetic use
C.1 Structure of methylene (carbenes)
1. The preparation of carbenes
:CH2 N N:+
Heat
Light:CH2 :N N:+
DiazomethaneÖصª¼×Íé
Methyleneor carbene
Nitrogen
1.
2. H3C C
CH3
CH3
OKHCCl3 + (CH3)3COH + :CCl3-
:CCl2 + Cl-
+ K+
Dichlorocarbene¶þÂÈ¿¨±ö
potassium tert--butoxide
C.2 Reactions of Methylene
Methylene reacts with alkenes by adding to the double bond to form cyclopropa
nes:CH2
Methyleneor carbene
+
Dichlorocarbene¶þÂÈ¿¨±ö
R
H
H
R
+
R
H
H
R
:CCl2
Cl Cltrans-
trans-