Topic 10 Organic chemistry
• Inorganic chemistry? Chemistry of life (now
biochemistry)  Carbon chemistry
• Introduction
• Alkanes
• Alkenes
• Alkohols
• Halogenalkanes
• Reaction pathways
10.1 Carbon molecules
•
•
•
•
Carbon has 4 valence electron’s (1s22s22p2)
Tetrahedral structures if single bonds
Planar triangular if double bond
Linear if triple bonded
Organic substances
• Carbon is often (almost always) covalently
bonded
• Other common atoms is hydrogen, oxygen,
nitrogen …..
• Molecules can be long chains or ring form
• Hydrocarbons: Compounds only containing
carbon and hydrogen
HYDROCARBONS
• Molecules containing only C and H
• Alkanes, alkenes, alkynes, arenes, cycloalkanes
Homologous series
•
•
•
•
Same general formula
Neighbouring members differ by –CH2Similar chemical properties
Gradation in physical properties, such as
boiling point
The first straight-chain alkanes,
general formula CnH2n+2
Name
Molecular
formula
Structural formula
Boiling
point (oC)
Methane
CH4
CH4
- 162
Ethane
C2H6
CH3-CH3
- 89
Propane
C3H8
CH3-CH2-CH3
- 42
Butane
C4H10
CH3-CH2-CH2-CH3
- 0,5
Pentane
C5H12
CH3-CH2-CH2-CH2-CH3
36
Hexane
C6H14
CH3-CH2-CH2-CH2-CH2-CH3
69
Explain the trend! Predict the boiling point of heptane!
Different ways of representing
structural formulas
Skeletal formula
Empirical formula?
Isomers
Same molecular formula but different structural formulas
Butane have 2 isomers:
• CH3-CH2-CH2-CH3
Butane
• CH3-CH-(CH3)-CH3
Methyl-propane
Methyl-group
C
H
3
H
C
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
3
1
2
3
4
5
6
7
1. Find the longest carbon chain and you have
the ”last name” of the compound: 7→ heptane
2. Find and name substituents: 1 metyl-group
3. Number the carbons in the chain so that
substituents gets as low no. as possible: the
methyl-group is attached at carbon no. 2
4. Put it together:
2-methyl-heptane
Ethyl-group
C
H
3
Methyl-group
C
H
2
H
C
C
H
C
H
C
H
C
H
3
2
3
1
2
3
4
5
C
H
2
1. Find the longest carbon chain and you have the
”last name” of the compound: 5→ pentane
2. Find and name substituents: 1 metyl-group and
1 ethyl-group
3. Number the carbons in the chain so that
substituents gets as low no. as possible: the
methyl-group is attached at C no. 3, and the
ethyl-group at C no. 2
4. Put it together:
3-etyl-2-methyl-pentane
Which names?
The names
2-methyl-propane
2, 3-dimethyl-butane
2-methyl-butane
2,2-dimethyl-butane
2,2-dimethyl-propane
2-methyl-pentane
10.2 Alkanes
• Homologous series of a saturated
hydrocarbon with only single bonds between
carbon atoms
• General formula CnH2n+2
• Low m.p. and b.p. due to only van der Waal´s
forces
• Often gases and liquids at
room temperature
• Low reactivity
Alkanes have high bond entalpies
and low reactivity
Bond
C-C
C-H
Bond
enthalpy
kJ/mol
348
412
Bond
Si-Si
Si-H
Bond
enthalpy
kJ/mol
226
318
Ge-Ge
Sn-Sn
188
151
Alkanes have low bond polarity
and low reactivity
Bond
C-C
C-H
C-F
Difference in
electronegativity
0
0,4
1,5
C-Cl
C-O
C-N
1,0
1,0
0,5
The higher the difference
in electronegativity,
the higher the reactivity
in reactions with e.g.
nucleophiles
(as we shall see later…)
About hydrocarbons
• Alkanes and other hydrocarbons are good
fuels
• Complete combustion: Hydrocarbons + oxygen
 Carbon dioxide + water +heat
• If oxygen is limited then incomplete
combustion: carbon monoxide, CO and
elementary carbon, C, may be formed
Combustion of octane
• Complete (with plenty of O2):
C8H18 + 25 O2
16 CO2 + 18 H2O
• Incomplete (not enough O2):
C8H18 + 9 O2
C + CO +2 CO2 + 9 H2O
Reactivity
• Alkanes can react with radicals- eg. chlorine in
UV-light
UV
Cl-Cl
2 Cl•
unpaired electron
• Compounds with unpaired electrons
are called free radicals and are very reactive
UV
• Cl-Cl
2 Cl•
homolytic fission
• A-B
A+ + Bheterolytic fission
The reaction of methane and chlorine by
radical reactions
1.
2.
3.
4.
2 Cl• + CH4  CH3Cl + HCl
2 Cl• + CH3Cl  CH2Cl2 +HCl
2 Cl• + CH2Cl2  CHCl3 + HCl
2 Cl• + CHCl3  CCl4 + HCl
• A mixture of chlorinated methanes is achieved
• Radical reactions involve an initiation step, one or
more propagation steps, and a termination step
Radical reactions
10.3 Alkenes
• Homologous series of unsaturated hydrocarbons
with one or more double bonds between carbon
atoms
• General formula CnH2n
• Low m.p. and b.p.
due to only
van der Waal´s forces
• Often gases and liquids at
room temperature
Ethene
CH2=CH2
Propene
CH3-CH=CH2
Butene
CH3-CH2-CH=CH2
1-Butene or But-1-ene
CH3-CH2=CH-CH3
2-Butene or But-2-ene
Pentene
CH3-CH2-CH2-CH=CH2
1-Pentene or Pent-1-ene
CH3-CH2-CH2=CH-CH3
2-Pentene or Pent-2-ene
Reactions of alkenes
• Reactive double bonds
• Low activation energy
• Addition and
polymerization reactions
Addition reactions with bromine and
hydrogen chloride
• H2C=CH2 + Br2 
colourless
red/brown
H2BrC-CH2Br
Spontaneous at NTP
colourless
Used as proof of C-C-double bonds
• H2C=CH2 + HCl  H3C-CH2Cl
Spontaneous at NTP
Addition reactions with hydrogen and
water
• H2C=CH2 + H2  H3C-CH3
E.g. Ni-catalyst. Industrially important when
transformation of vegetable oil to margarine
• H2C=CH2 + H2O  H3C-CH2OH
Catalyst: H2SO4, H3PO4 or Al2O3
~300oC, 7 MPa. At 1 atm the reversed reaction is
favoured. Synthesis of alcohols
Polymerisation reactions
• Alkenes forming plastics, making plastics
• Radical reactions involving Cl2 and UV-light
• Initiation:
UV
Cl-Cl
2 Cl•
• Propagation; adding monomers to a long chain, e.g.
H2C=CH2 + Cl•  •H2C-CH2Cl
monomer
•H2C-CH2Cl + H2C=CH2  •H2C-CH2-H2C-CH2Cl
•H2C-CH2-H2C-CH2Cl + H2C=CH2 •H2C-CH2-H2C-CH2H2C-CH2Cl
Termination
Two radicals meet and a bond is formed.
R-CH2• + R’-CH2•  R-CH2-CH2-R’
• The polymer is ready!
Addition polymerisation reactions (I)
High pressure
n
Ethene monomer
Cl
n
Chloroethene monomer
n
Propene monomer
*
n
*
Repeating unit of polyethene, PE
n
*
*
Cl
Repeating unit of polychloroethene (polyvinylchloride, PVC)
*
n
*
Repeating unit of polypropene (PP)
Addition polymerisation reactions (II)
n
n
*
P h e n y le t h e n e m o n o m e r
R e p e a t in g u n it o f p o ly p h e n y le t h e n e ( p o ly s t y r e n e , P S )
F
F
n
F
F
F
T e t r a f lu o r e t h e n e m o n o m e r
*
*
F
n
*
F F
R e p e a t in g u n it o f p o ly t e t r a f lu o r e t h e n e ( P T F E )
Teflon
Benzene ring
• Identify when present in structural formula, phenyl
ring
Functional groups
• C-C double and triple bonds, phenyl ring
• Other elements bonded in different ways with
the carbon chain; alcohol, aldehyde, keton,
carboxylic acid, amine, ester, halide
• Give the molecule other chemical and physical
properties
10.4 Alcohols
• The functional group –OH
• Name: stem + the suffix –anol (or as prefix: hydroxy)
• H-bonds => higher b.p., smaller ones (C1-C3)
are water-soluble
• Methanol
CH3OH
Wood spirit, formed by pyrolysis of wood. Highly
toxic!
• Ethanol
CH3-CH2-OH
Alcohol, formed during fermentation of sugar.
Technically very important;
In drinks, as a solvent,
desinfectant and fuel
Propanol
• CH3-CH2-CH2-OH
1-propanol or propan-1-ol a primary alcohol
• CH3-CHOH-CH3
2-propanol or propan-2-ol a secondary alcohol
Isopropanol, used as windscreen de-icer
Butanol
• CH3-CH2-CH2-CH2-OH
1-butanol or butan-1-ol
Non-water soluble
• CH3-CCH3OH-CH3
2-metyl-2-propanol or 2-metylpropan-2-ol, a
tertiary alcohol
Water soluble
Combustion
Alcohol + Oxygen  Carbon dioxide + water
CH3-CH2-OH + 3 O2

2 CO2 + 3 H2O
Redox reactions in organic chemistry
• The carbon with a functional group (eg. –OH)
will be oxidised first
• Oxidation: Add oxygen and/or remove
hydrogen from the carbon
• Reduction: Add hydrogen and/or remove
oxygen from the carbon
oxidation 
reduction 
Alcohol
Aldehyde
CH4
CH3OH
HCHO
H-COOH
CO2
Methane
Methanol
Methanal
Methanoic
acid
Carbon
dioxide
H
H
H
C
H
H
H
C
H
Carboxylic acid
O
O H
H
O
C
H
H
O
C
O H
C
O
The more bonds to oxygen, the higher oxidation state of a carbon
Oxidation of alcohols
• Primary alcohol  Aldehyde Carboxylic acid
• Secondary alcohol  Ketone
• Tertiary alcohol  no oxidation (unless C-Cbonds are broken)
K2Cr2O7, Potassium dichromate,
a common oxidizing agent
H
H C
H
H
H
C O
H H C
H
O
H
C H H C
H
CH3CH2OH + Cr2O72- + H+  CH3CHO 
C O
H
H
CH3COOH + Cr3+ + H2O
Reactive.
Stable.
Distill of
when formed
Reflux
Other oxidizing agents KMnO4, CuO, CuSO4
O
Aldehyde
• The functional group –CHO or
• Name: stem + suffix: -anal
• Dipoles => slightly higher bp’s, smaller ones
are water-soluble etc.
• Quite reactive compounds
• Methanal H-CHO
• Ethanal CH3-CHO
• Formed by light oxidation of primary alcohols
Ketone
• The functional group –CO- or
• Name: stem + suffix: -anone
• Dipoles => slightly higher bp’s, smaller ones
are water-soluble etc.
• Propanone (acetone) CH3-CO-CH3
• Pentane-2-one CH3-CO-CH2-CH2-CH3
• Formed by oxidation of secondary alcohols
Carboxylic acids
• The functional group –COOH or
• Name: stem + suffix: -anoic acid
• H-bonds => higher bp’s, smaller ones are watersoluble etc.
• Acidic reactions
• Methanoic acid H-COOH
• Ethanoic acid CH3-COOH
• Formed by strong oxidation of primary alcohols
Salt of Carboxylic acids
•
•
•
•
•
Salt form: -COO- or
Name: stem + suffix: -oate ion
Methanoate H-COOEthanoate CH3-COOFormed by reaction of carboxylic acid and
base:
NaOH + CH3COOH
Na+ + CH3COO-
Halogenoalkane
• Functional group: -X (-F, -Cl, -Br, -I)
• Name: e.g. prefix: Chloro- + alkane
• Chloromethane CH3-Cl
• Bromoethane CH3-CH2-Br
Ester
• Identify when present in structural formula
• Functional group: -COOC-
• Alcohol + carboxylic acid  ester + water
• Condensation reaction or esterification
Amines
• Identify when present in structural formula
• Relatives to ammonia; weak base
• Functional group –NH2
• H-bonds => higher bp’s, smaller ones are
water-soluble etc.
• Name: stem + suffix: -ylamine (or prefix amino-)
• Ethylamine CH3-CH2-NH2
10.5 Halogenoalkanes
Reactions
Bond
enthalpy
kJ/mol
Bond in
CH3-CH2-X
484
338
276
238
C-F
C-Cl
C-Br
C-I
C—X
d+ d=> Iodine compounds most reactive
Nucleophiles and electrophiles- often
needed in organic reactions
• Nucleophile- nucleus
lover
• Has free electronpair
and whole or part
negative charge
• The larger the negative
charge - the better the
nucleophile
• Eg: C=C, H2O, -OH, -CN,
NH3
• Electrophile-electron
lover
• Has whole or part
positive charge
• The larger the positive
charge - the better the
Electrophile
• Eg: C=O, H+, C-Cl,
Substitution reactions
CH3-CH2-Cl (aq) + -OH (aq)  CH3-CH2-OH (aq) + Cl- (aq)
• The nucleophilic hydroxide ion, OH-, attacks the positively
charged, electrophilic carbon
• Curly arrows are used in mechanisms to show how electron
pair moves
• The substitution reaction can proceed by two different
pathways, mechanisms SN1 and SN2
SN2
• Substitution Nucleophilic bimolecular
• Bimolecular = two species in the rate
determining step. Rate = k [org]*[Nu]
• Favoured when primary halogenoalkanes. Less
steric hindrance from neighbouring groups.
• HL: If reactant is chiral (optic active) the
product is also optic active. But with inversion
in the structure.
SN2 Mechanism
Nucleophile attack
Transition state
Leaving group
Bonds breaks and forms
Enthalpy diagram for SN2
Enthalpy
Reaction coordinate
SN1
• Substitution Nucleophilic monomolecular
• Monomolecular = one species in the rate
determining step. Rate = k [org]
• The rate determining step is the formation of
a carbocation, an intermediate, which is only
stable on a tertiary carbon
• Favoured when tertiary halogenoalkanes
(electrophile). The formed carbocations are
stabilised by inductive effect.
Stability of carbocations
Mechanism for SN1-reaction
Heterolytic fission
Enthalpy diagram for SN1-reaction
.
10.6 Reaction pathways
• Deduce reaction pathway given the starting
materials and the product
• Conversions with more than two stages will
not be assessed. Reagents, conditions and
equations should be included
• The compound and reaction types in this topic
are summarized in the scheme on the next
slide
1-3. Substitution via radical mechanism. Induced by homolytic cleavage of Cl2
by UV-light.
4. Addition reaction. Hydrogen halide, spontaneous at STP
5. Addition reaction. H2 and Ni-catalyst
6. Addition reaction. Halogene, spontaneous at STP
7. Poly-addition. Radical mechanism. Initiation, prolongation and termination
8. Substitution reaction with NaOH; SN1 or SN2
9. Oxidation of primary alcohol with acidified K2Cr2O7. Distillation to get the
product
10. Oxidation of primary alcohol with acidified K2Cr2O7. Reflux to get the
product
11. Oxidation of secondary alcohol with acidified K2Cr2O7