chapter11 introduction of organic chemistry
TRANSCRIPT
3
At the end of this lesson, students should be able to:
Define structural formula.
Identify classes of carbons (10,20,30,40) and hydrogens
(10,20,30).
Draw structural formula in the form of expanded condensed and skeletal structures based on molecular formula.
Chemical Formula represented by :
EMPIRICALFORMULA
MOLECULARFORMULA
STRUCTURALFORMULA
• simplest formula for a compound
• shows the types of atoms present and
their relative numbers
• it may or may not be the actual chemical
formula of a molecule
Empirical Formula
• shows the actual number of atoms
• for all elements present in the molecule
e.g.
C2H4, C2H4O2
Molecular Formula
•shows the actual arrangement of atoms
in the molecule can be drawn in the form of :
expanded structurecondensed structure
skeletal structure
Structural Formula
shows all the covalent bonds
between the atoms
does not represent the actual shapes of the molecules
EXPANDED structure
Examples
Covalent bondC
H
H
H H
C
H
H
HC
H
H
H
Methane, CH4
Ethane, C2H6
C C
H H
H H
Ethene, C2H4
C CC
H
H
H C
H
H
H
2-propene, C4H8
H H
does not show single bonds between C and H atoms
BUT double and triple bonds are shown
all atoms which attached to a particular C
are written immediately after the C
condensed structure
Example 1
C C
H H
H H
Ethene, C2H4
H2C=CH2
C CC
H
H
H C
H
H
H
2-propene, C4H8
H H
CH3CH=CHCH3
Example 2
Example 3
2-Chlorobutane
C CC
H
H
H C
H
H
H
H Cl
CH3CH2CHCH3
H H @CH3CH2CH(Cl)CH3
Cl
if there are 2 or more similar groups
bonded
to the same C atom,
the group is enclosed in brackets and a subscript numeral
is used to indicate its number
Example
Pentane, C5H12
C CC
H
H
H C
H
H
H
H H
CH3(CH2)3CH3
H H
C
H
H
bonds are represented as lines C atoms assumed to be at the
beginning and end of a line
and where 2 or more lines meet does not show C and H atoms BUT
functional groups and atoms other than C and H
MUST be shown
SKELETAL structure
CH3CH(Cl)CH2CH3
Cl
C1
C2
C3
C4
H2C CH2
H2C CH2
CH2 = CHCH2OH
OH
C1 C2
C3
(i)
(ii)
(iii)
1 2 3 4
1 2
34
Examples
describes how atoms of the molecules are
arranged in space
e.g. Bromomethane
C
Br
H
H
H 2-dimensional structure
3-Dimensional structure
C
Br
HHHC
H
BrHHC
H
HBrH
Represent a bond on the plane of the paper
Represent a bond comingout of the paper
Represent a bond pointingto the back of the paper
3–Dimensional Structure of Bromoethane
CLASSIFICATION OF CARBON AND HYDROGEN ATOMS
Depending on the number of C atom bonded to it
Type of C atom No. of C atoms bonded to it Example
None12
3
4
MethylPrimary (10)Secondary (20)
Tertiary (30)
Quarternary (40)
OHH3CCH3H3C
CH2 CH3H3CCH CH3
CH3
H3C
CCH3
CH3
CH3
H3C
Classification of C atoms
H atom is also classified as 1o, 2o and 3o
depending on the class of C bonded to it e.g.
CH
CH2
CH3
H3C CH3
1o
2o
3o
Classification of H atom
1o2o
3o
1o
1o
However, there is no 40 H
21
1. Draw skeletal structure for each condensed structure given below:
CH3 CH2CH2CH3
=1 2 3 4
CH3 CH2 C N
= N
CH2 = CHCH2OH
OH
=1 2 3
22
=CH3 CH2CH CH2CH3CH3
1 2 3 4 5
CH3 CH2C-CH3 O O
=
CH2CHClH2C
H2C CH2
Cl
=
23
2.A hydrocarbon Q has the molecular formula of C4H10 . Write all the possible structural formulae of Q in the form of :
i. condensed structures
ii. skeletal structuresCH3 CH2CH2CH3
CH3 CH(CH3 )2
CH3 (CH2)2 CH3
i.
ii.
or
CH C C CH2 C CH3
H
H
H
H H
CH3 CH3
CH3
10 20
4030
1o carbon - 5 2o carbon - 23o carbon - 14o carbon - 1
10 10
10
10
20
24
26
At the end of this lesson, students should be able to:
Define functional group.Identify functional group
Explain general characteristics of homologous serries.
Classify organic compounds according toTheir functional groups.
Define homologous serries.
atoms or group of atoms in an
organic molecule which characterised the molecule
and determine the chemical properties of organic
compounds
Functional Group
Important for 3 reasons :
the sites of chemical reaction
serve as a basic for naming organic compounds
the units by which organic compounds are
divided into classes
29
Homologous Series Alkene Alkyne Arene
Functional Group
C = C (carbon-carbon double bond)
C ≡ C (carbon-carbon
triple bond)
(aromatic ring)
General Formula CnH2n CnH2n-2 CnH2n-6
IUPAC Nomenclature -ene -yne -benzene
Example CH2= CH2 ethene
CH ≡ CH ethyne methylbenze
ne
CH3
Benzene ring
30
Homologous Series Haloalkane Alcohol Ether
Functional Group
C–X halogen
–OH (hydroxyl)
–O– (alkoxy)
General Formula CnH2n+1X CnH2n+1OH CnH2n+2O
IUPAC Nomenclature
haloalkane alkanol alkoxy
alkane
Example CH3CH2Clchloroethane
CH3CH2OH ethanol
CH3OCH3 methoxy methane
31
Homologous Series Aldehyde Ketone Nitrile
Functional Group
–C–H
carbonyl
–C–
carbonyl
–C≡N(cyano)
General Formula CnH2nO CnH2nO CnH2n+1CN
IUPAC Nomenclature alkanal alkanone alkanonitrile
Example CH3C-H
ethanal
CH3COCH3
propanone
CH3CH2C≡Npropanonitril
e
O O
OO
32
Homologous Series Carboxylic Acid Ester
Functional Group
–C–OH (carboxyl)
–C–O–C
General Formula CnH2nO2 CnH2nO2
IUPAC Nomenclature alkanoic acid alkyl alkanoate
Example CH3C–OH
ethanoic acid
CH3C–OCH3
methyl ethanoate
O (carboalkoxy)
O
O
O
33
Homologous Series Acyl halide Anhydride
Functional Group –C–X
–C–O–C–
General Formula CnH2n+1COX (CnH2n+1CO)2O
IUPAC Nomenclature alkanoyl halide alkanoic anhydride
Example
CH3C–Cl
ethanoyl chloride
CH3C–O–C-CH3
ethanoic anhydride
O OO
O OO
34
Homologous Series Amine Amide
Functional group
–C–N– (amino)
–C–N–
(carboxamide)
General Formula CnH2n+1NH2 CnH2n+1CONH2
IUPAC nomenclature -amine -amide
Example CH3NH2 methanamine
CH3CONH2
ethanamide
35
C
O
CC
CHCH2C-CH3
OO
1. Circle and name all the functional groups present in the following molecules.
a.
aromatic ring
carbonyl
Carbon-carbon double bond
carboalkoxy
36
b.
CH2CH2CHCH2C-OCH3
O
NH2
O
Br
carbonyl
Carbon-carbon double bond
amino
carboalkoxy
halogen
37
2. With reference to the following structural formula:
CH3CH2CH=C-CH2CH2C-NH2 B
rO
a. Give the molecular formula.
b. Write its skeletal formula.
C7H12ONBr
Br
O
NH2
38
CH3CH2CH=C-CH2CH2C-NH2 B
rO
Carbon-carbon double bond
halogen
carboxamide
c. State 3 functional groups that exist in the molecule.
39
1. Write and name the functional groups that exist in the following molecule :
O
CH2CH2CHCH2COCH3
O
NH2
carbonyl
Carbon-carbon double bond
carboalkoxy
amino
40
OH
O CH3
CO H O H O
║ │ ║NH2 – CH-C-N-CH-C-OH │ │ H CH3-C=O
2. Identify the functional groups in the following compounds. Write and name the class of the compounds.
Homologous Series
A group of compounds with the same functional group
Homolog
Members of a homologous series
FIRST THREE MEMBERS OF THE SERIES
CH3OH Methanol
Example: ALCOHOLS
(Homologous Series)
C2H5OH Ethanol
C3H7OHPropanol
(Homolog)
A homologous series has four features :
share the same general formulaExample:
saturated aliphatic ALCOHOL CnH2n+1OH, where n = 1, 2, 3, etc.
(1)
n = 1 CH3OH methanoln = 2 C2H5OH ethanol
n = 3 CH3CH2CH2OH propanol
Have same functional group. Thus, have the same chemical properties and can prepared by same methods contain the –OH group (Hydroxyl
Group) react with carboxylic acids to give
esters can be prepared by heating dilute
sodium hydroxide solution with an appropriate alkyl halide
Example: ALL Alcohols
(2)
Each homolog differs from the homolog above or below it in the series by – CH2
CH4 methaneCH3CH3
ethaneCH3CH2CH3 propane
(3)
Example 1
HCHO methanal
Example 2
CH3CH2CHO propanal
CH3CHO ethanal
As the size of the molecules increases, boiling point and melting point increases
show a gradual change in physical properties as molar mass increases
(4)
Example
Compound Boiling pointCH4 - 162CCH3CH3 -
88.2C
48
At the end of this lesson, students should be able to:Define isomerism.
Explain constitutional isomerism.
Define and identify chirality centre and enantiomers.
Explain optical activity of a compound.
Draw a pair of enantiomers using 3-D formula.
Define stereoisomerism.
Describe and identify cis-trans isomerism.
ISOMERISM
Structural/Constitutional Isomerism Stereoisomerism
Chain Isomerism
Positional Isomerism
Functional Group Isomerism
DiastreomerEnantiomer
cis-transisomerism
otherdiastereomers49
ISOMERISM
Structural isomerism
Stereoisomerism
50
the phenomenon of the existence of 2 or more compounds with the same molecular formula
but different in structures
The different compounds : called isomer
The isomerism resulting from different order of attachment of atoms
The isomers differ in their bonding sequence; their atoms are connected differently
Chain Isomerism
Positional Isomerism
Functional Group Isomerism
51
same functional group same homologous series same chemical properties but different physical properties linear or branch chain
a) Chain isomerism different carbon chain i.e continous-chain or branched-chain.
Example : C5H12
CH3 CH2 CH2 CH2 CH3
CH2 CH3CH3 CHCH3
CH3 C
CH3
CH3
CH3
Linear form
Branch form
3 Isomers
Characteristic of Chain Isomers
Chemical properties isomers show same chemical properties
because it has same functionalPhysical properties
density and boiling point show trends according to the degree of branching
“straight” chain isomers have higher boiling points
than branched chain isomers the greater the degree of branching, the lower
the boiling point
branching decreases the effectiveness of intermolecular attractive forces, so less
energy has to be put in to separate the molecules
Boiling PointCharacteristic of Chain Isomers
- 0.5°Cstraight chain
greater branching = lower boiling point
-11.7°C branched
• same skeletal structure• different position of the functional group or
substituent groupsExample : C3H7Cl
CH3CH2CH2Cl 1-chloropropane CH3CHCH3 2-chloropropane Cl
Example : C4H8
CH2 = CHCH2CH3 1-butene CH3CH = CHCH3 2-butene
b) Positional isomerism
C8H10
1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene
CH3
CH3
CH3
CH3
CH3
CH3
58
same molecular formula have different functional groups belongs to different homologous series different chemical and physical properties
c) Functional Group isomerism
Alcohols and Ethers
Aldehydes and Ketones
Carboxylic Acids and Esters
Compounds which exhibit functional group isomerism
Alkene and Cycloalkane
ExampleALCOHOLS and ETHERS
Name ETHANOL METHOXYMETHANEClassification ALCOHOL ETHER
Functional Group -OH -OR
Physical polar O-H bond gives rise no hydrogen bondingproperties to hydrogen bonding. low boiling point
get higher boiling point insoluble in water and solubility in water
General Formula CH3CH2OH CH3OCH3
Examples
C2H6O
C3H6O
C3H6O2
ethanol dimethyl ether
propanal propanone
propanoic acid methyl ethanoate
CH3CH2OH CH3OCH3
CH3 CH2C
O
H
CH3CH2C
O
OH
CH3 CO
CH3
CH3 CO
O CH3
62
Exercise:1.State how many are isomers with the
following molecular formulae, identify the type of isomerism and draw the structural formula of the isomers.
a) C5H10
b) C5H10O2
c) CH3CH=C(Cl)CH3
d) C4H6Cl2 e) CH3CH2CH(OH)CH(Br)CH2CH3
63
Chain Isomerism
Positional Isomerism
The isomers differ in the carbon skeleton (different carbon chain i.e continous-chain or branched-chain).
The isomers have a substituent group/ functional group in different positions.
The isomers have different functional groups and belong to different homologous series with the same general formula.
Functional Group
Isomerism
Stru
ctur
aliso
mer
ismSUMMARY
64
The isomerism resulting from different arrangement of atoms in molecules.
Isomers have the same bonding sequence, but they differ in the oriention of their atoms in space.
Enantiomer Diastereomer65
cis-isomer trans-isomer
C CCl
H H
ClC C
Cl
H Cl
H
Same side
opposite side
same atom or groups of atom on the same
side
same atom or groups of atom on the opposite side
a) DiastereomerCis-Trans Isomerism/geometric isomerism
66
♫ restricted rotation about a C=C, double bond in alkenes, or a C-C single bond in cyclic compounds.
♫ each carbon atom of a site of restricted rotation has two different groups attached to it.
The requirements for geometric isomerism :
67
trans-2-butene cis-2-butene
C CH
CH3 H
CH3
C CH
H3C CH3
H
cis-1,2-dimethylcyclohexane
trans-1,2-dimethylcyclohexane
H
CH3
H
CH3
H
CH3
CH3
H
Examples :
68
H
Cl
H
Cl
H
Cl
Cl
Hcis-1,3-dichlorocyclohexane
trans-1,3-dichlorocyclohexane
69
cis-trans isomers are two different compounds different physical properties :
melting point : trans-isomer > cis-isomer boiling point : trans-isomer < cis-isomer stability : trans-isomer > cis-isomer
similar chemical properties (have the same functional group) cis-isomer : polar molecules; trans-isomer : non-polar molecules
Characteristic of Cis-Trans Isomers
If there are 3 different groups attached to the doubly bonded C,the following rule applies:
higher-priority groups are on the same side
higher-priority groups are on the opposite site
cis-isomer trans-isomer
71
C CH
CH3 CH2CH3
CH3
C CH
CH3 CH3
CH2CH3
Higher priority groups
Atom with a higher atomic number is in higher priority than an atom with lower atomic number
Higher priority groups
cis-3- methyl-2-pentenetrans-3- methyl-2-pentene72
♫ If one of the doubly bonded carbons has 2 identical groups, geometric isomerism is
not possible.
2-methyl - 2- butene
C CH
CH3 CH3
CH3
C CH
H CH2CH3
CH3
2-methyl - 1- butene
No cis – trans isomer
73
® The chiral molecule and its mirror image are
Enantiomers
Molecules/objects that are not superimposable with their mirror images are said to be
chiral.
hands glovesshoes
74
have one or more chiral carbons. A chiral carbon has four different
atoms or group atoms attached to it.
P
CQR
S* PQRS
*designates chiral centre
b) Enantiomers Are a pair of stereoisomers that are mirror-image but not superimposable.
75
Enantiomers i) 2-butanol
C*CH2CH3
H3COH
HC
CH2CH3
CH3HOH
enantiomers
CH3 CH CH2CH3
OH
76
*
ii) 2-hydroxypropanoic acid
CCOOH
H3COH
HCCOOH
CH3HOH
enantiomers
CH3 CH COOH
OH
77
*
Enantiomer
Diastereomer
a pair of mirror-image molecules that are not superimposable.
A pair of enantiomers have identical chemical & physical properties but differ in the direction of rotation of plane- polarized light. Stereoisomers that are not mirror images of each other
All physical properties of diastereomers are usually different from one another.
Stre
reoi
som
erism
78
OPTICALLY ACTIVE molecules which are optically active are
measured using : polarimeter able to rotate the plane-polarised light to be optically active molecules must contain at least one chiral C
Plane – polarised Light is composed of waves that vibrate in only one plane.
Plane – Polarised Light
A beam of light is passed through a piece of polariser prism,the emergent light vibrates in a single plane.The light is called plane-polarised light.
80
Substances that could rotate the plane-polarized light are called Optically active compounds . 81
PLANE-POLARISED LIGHT
Dextrorotatory isomer(d or +)
Laevorotatory isomer(l or -)
Clockwise rotation
Anti-Clockwise rotation
i) molecule contains a chiral carbon/chirality centre
ii) molecule is not superimposable with its mirror image.
The requirements for optically active compounds :-
A pair of enantiomer rotate the plane of polarised light by exactly the same degree
but in opposite directions.83
PRACTICE EXERCISEFor the following questions match each definition to a term from the list below.
a. Optically activeb. Diastereomer
c. Chirality centre
2. Stereoisomers that are not mirror images3. Is an atom in a molecule that is bonded to 4 different atoms or groups of atoms
1. Describes organic molecules which rotate plane-polarised light Optically
active Diastereomer
Chirality centre
86
At the end of this lesson, students should be able to:Explain covalent bond
cleavage:homolytic and heterolitic.
State relative stability of 10,20 and 30 free radicals, carbocations nad carboanions.
Define electrophile and nucleophile.
State the main types of organic reactions.
Explain the inductive effect of alkyl group
Towards the stabilities of carbocations
and carboanions.
87
• involve the breaking and making new covalent bonds
• two means of electron transfer during the breaking of covalent bond
represents the transfer of one electron.
represents the transfer of two electrons or a pair of electrons.
:
:
88
• Occurs in a non-polar bond
• involve two atoms of similar electronegativity.
• single bond breaks symmetrically,
• leaving each atom with one unpaired electron.
• Forms free radicals.
Occurs in a polar bond involve two atoms of
different electronegativities.
single bond breaks unsymmetrically,
both the bonding electrons are transferred to the more electronegative atom.
Forms cation and anion.
89
Homolytic Cleavage
Heterolytic Cleavage
A – B A B+ A – B A– B++
A – B A+ B–+
A is > electro-ve
B is > electro-ve
90
Cl – Cla.
H – CH3b.
2 Cl
H CH3+
H – Cl
(CH3)3C – Br
+ –
+ –
+H+ Cl
+ Br(CH3)3C+
uv
uv
Homolytic Cleavage
Heterolytic Cleavage
91
Unstable and highly reactive species.Formed during a reaction as a result of bond cleavage.
Three types:
Carbocation or carbonium ion
Carbanion Free radical
92
Reactive species with unpaired electronAn e deficient speciesResults from homolytic cleavageExamples
Reactive species with + charge on C atom An e deficient speciesResults from heterolytic cleavageExamples
Reactive species with - charge on C atom An e rich speciesResults from heterolytic cleavageExamples(CH3)3C
+ CH3+
(CH3)2CH+(CH3)3C- CH3
-
(CH3)2CH-
(CH3)3C CH3
(CH3)2CH
93
Carbocations, carbanions & free radicals are classified as 1o , 2o or 3o based on the number of adjacent C atoms of the:
positively charged C atom (for carbocation)
negatively charged C (for carbanion)
carbon atom with an unpaired electron(for free radical)
94
Carbocations and free radicals are electron-deficient (lack an octet around the C atom)
Both are stabilised by the electron-donating effect of alkyl groups, –R, The more highly substituted carbocations or free radicals are more stable.
95
(3o
)(2o
)(1o
)methylium
Decreasing stability
RRCR
+ H CH
+H
CH
+R
RHCH
+R
(CH3)3C
+
(3o
)(1o
)(2o
)
+(CH3)2CH
+CH3CH2
+CH3
Stability of carbocation
96
The stability of benzylium ion (a 1o aromatic carbocation) is comparable to that of 3o aliphatic carbocation.
CH2+
CH2+ CH2
+CH2+
CH2
+
Reason The positive charge on C is resonance-stabilised:
97
3o 2o 1o
(CH3)3C
(CH3)2CH
CH3CH2
CH3
RRCR
H CH
H
CH
R
RHCH
R
Decreasing stability
methyl radical
3o1omethyl radical
2o
98
Carbanions are high electron density species. (electron-rich)
Electron-donating groups ( e.g. alkyl group, –R , etc) destabilise a carbanion.
Electron-withdrawing groups (e.g. Halogen) stabilise carbanions ( reduces the electron density of carbanions)
The order of stability is the opposite to that of carbocations and free radicals
99
3o 2o 1o methyl anion
(CH3)3C
– –(CH3)2CH
–CH3CH2
–CH3
Increasing stability
RRC:R
– C:H
RR –
HC:H
R – H C:H
H–
3o 1o methyl anion
2o
100
Arrange the following species in order of increasing stability:
CH2+ CH3+ CH3
+
(CH3)2CCH2CH3
+ (CH3)3CCHCH
3
+
(CH3)3CCH2
+
a.
b.
1o 3o 2o
3o
2o
1o
101
CH2+ CH3
+c. CH2
+
(CH3)2CCH2CH3
+d.
CH3CHCH2CH2
+
CH3
CH2CHCH2CH3
+
CH3
1o
3o
CH3CHCHCH3
+
CH3 2o
1o
1o aromatic
2o
1o
102
There are 2 types of chemical reagents
Electrophile (E+) Nucleophile (Nu-)
“ loves electron ” “ loves nucleus ”
An electron-deficient species and electron-pair acceptor that attacks part of a molecule where the electron density is high (nucleophilic site)
An electron-rich species and electron-pair donor that attacks a part of a molecule where the electron density is low (electrophilic site)
103
Cations H+, H3O+, NO2
+, X + All carbocations R+
Lewis acidsAlCl3 , FeCl3 , BF3 , ZnCl2 , H2O Oxidising agents Cl2 , Br2 etc.
Electrophile Nucleophile
AnionsOH–, RO–, Cl– , CN– All carbanionsR – (species with a negative charge on carbon atoms).Lewis basesspecies which can donate lone pair electrons : NH3 , H2O, H2S, RNH2
104
Molecules with low electron density around a polar bond such as:
Electrophilic Sites in Organic Molecules
carbonyl group
haloalkane
hydroxyl group
C Oδ+ δ-
C Xδ+ δ-
C OH+δ δ-
105
Molecules with high electron density around the C-C multiple bond:
C = C
C C
Alkenes
Alkynes
Aromatic compounds
Nucleophilic Sites in Organic Molecules
106
Identify the following species as nucleophile or electrophile:
CH3OCH2CH3 AlCl3
CH3CH2OH SO3
CO2
CH3CH=CH2
CH3CH2O– (CH3)2CH +
C6H5N2+
Nu.E
E / Nu
Nu. E E
Nu. E
Nu.
107
SubstitutionRearrangementElimination
4 main types of chemical reactions
Addition
electrophilic
nucleophilic
electrophilic
nucleophilic
Free radical
108
A reaction in which atoms or groups add to adjacent atoms of a multiple bond (double or triple bond). • involve breaking of one bond
to form two sigma bonds
109
atoms or groups of atom are added to adjacent atoms of a multiple bond
atoms or groups of atom are added to adjacent atoms of a multiple bond
Initiated by electrophileTypical rxn for alkene
Initiated by nucleophileTypical rxn for carbonyl
110
Reagent : electrophileSubstrate : unsaturated compounds with
nucleophilic sites such as C=C or C≡C.Note : typical reaction of alkenes
CH2= CHCH2 CH3CHBrCH2+ HBra.
CH2=CH2 CH2(Br)CH2 (Br)+ Br2b.
CH3 + H2O CH3
OHc.
111
Reagent : nucleophileSubstrate : unsaturated compounds
with electrophilic sites such as –C=O
Note : typical reactions of aldehydes & ketones
a.
CH3CHO
+ NH3 CH3CHNH2
OH
b. CH3CCH3
O+ HC
NCH3C-CH3
OH
CN
112
A reaction in which an atom or a group in a molecule is replaced by another atom or group of atoms from the reagent.
113
+ Br2Fe Br + HBra
.
CH3+NO2+ CH3
NO2
b.
Reagent : electrophileSubstrate : aromatic nucleus, stable
with high electron density.Note : typical reaction of
aromatic compounds.
114
CH3CH2Cl + NaOH
a.
CH3CH2OH + NaCl
Brb. + KCN
CN + KBr
+ SOCl2
c. + H2O
CH3CHOHCH3
CH3CHClCH3
Reagent : nucleophilicSubstrate : saturated compounds
with polar bonds as functional group
Note : typical reactions of haloalkanes and alcohols.
115
CH3CH2CH3 + Cl2
a.
+ HCluv CH3CHCH
3 Cl
b. CH3 + Br2
uv
CH3
Br + HBr
Substitution which involves free radical as intermediate species.
Typical reaction of alkanes.
116
A reaction in which atoms or group of atoms are removed from adjacent carbon atoms of a molecule to form a multiple bond (double or triple bond)
Typical reaction of alcohols & haloalkanes.
Product: Unsaturated molecules.
117
CH3CHOH CH3
conc. H2SO4 CH2=CHCH
3
+H2Oi.
Br conc. KOHethanol, ∆
+HBrii.
118
A reaction in which atoms or groups in a molecule change position.
Occurs when a single reactant reorganises the bonds and atoms
Occur in reactions involving the formation of a carbocation intermediate
119
c. OH-C CH2C
H3
CH3
Cl
CH3
a. CH3CCH3
OCH3C=CH2
OH
tautomerism
b. CH3CHCH2OH CH3
conc. H2SO4
C CH3CH3
OH
CH3
CH3CH CHCH3CH3
Cl
120
State the type of reaction for each of the following reactions:
(CH3)3C-Br + NaOH
(CH3)3C-OH+ HBr
a.
CH3C–CH2OH CH3C=CCH3 CH3CH3
CH3 CH3
+ H2O
conc. H2SO4
b.
Elimination
Nucleophilic substitution
121
OH
HO
CH3CH3Cl
AlCl3+ HCl
+ Br2(aq)
CH3CH=CCH3 CH3
CH3CHCCH3 CH3
OH
Br
c.
d.
Electrophilic substitution
Electrophilic addition
122
CH3C–CH3 O
e.
CH3C–CH3 OH
CN+ HCN
+ Br2
Br
+ HBr
f.u
Nucleophilic addition
Free radical substitution
123
State the type of reaction for each of the following
reactions :
b. CH2 = CH2 + HBr CH3CH2Br
c. C6H6 + CH3Cl C6H5CH3 + HCl
e. CH3CH2Cl + NaOH CH3CH2OH + HCl
a. CH2 = CHOH CH3CHO
d. CH3CH2OH CH2 = CH2 + H2O
[5 marks]
rearrangement
Electrophillic addition
Electrophillic substitution
Elimination
Nucleophillic substitution
124
Nucleophilic substitution
Nucleophilic addition
Electrophilic substitution
+ HNO3
Conc H2SO4
NO2
CH3COCH3 + HCN CH3 C CH3
CN
OH
CH3CH(OH)CH2CH3
CH3CH(Cl)CH2CH3
+ SOCl2
125
Substitution
RearrangementElimination
Addition
electrophilic
nucleophilic
electrophilic
nucleophilic
Free radical
(alkene/alkyne)
(aldehyde/ketone)
(alkane)
(aromatic ring)
(R-OH, R-X)
(R-OH, RX alkene)
(Rxn involve C+ / C intermediates)