Topic 10 Organic chemistry• Inorganic chemistry? Chemistry of life (now
biochemistry) Carbon chemistry• Introduction• Alkanes• Alkenes• Alkohols• Halogenalkanes• Reaction pathways
• Carbon has 4 valence electron’s (1s22s22p2)• Tetrahedral structures if single bonds• Planar triangular if double bond• Linear if triple bonded
10.1 Carbon molecules
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 –CH2-• Similar chemical properties• Gradation in physical properties, such as
boiling point
Name Mole-cular 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
The first straight-chain alkanes, general formula CnH2n+2
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
1. Find the longest carbon chain and you have the ”last name” of the compound: 7→ heptane
2. Find and name substituents: 1 metyl-group3. 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
CH3 CH
CH3
CH2 CH2 CH2 CH2 CH3
Methyl-group
1 2 3 4 5 6 7
CH3 CH
CH2
CH
CH2
CH2 CH3
CH3
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
Ethyl-group
1 2 3 4 5
Methyl-group
Which names?
The names
2-methyl-propane 2-methyl-butane 2,2-dimethyl-propane
2, 3-dimethyl-butane 2,2-dimethyl-butane 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 entalpiesand low reactivity
Bond Bond enthalpy kJ/mol
Bond Bond enthalpy kJ/mol
C-C 348 Si-Si 226C-H 412 Si-H 318
Ge-Ge 188Sn-Sn 151
Alkanes have low bond polarityand low reactivity
Bond Difference in electro-negativity
C-C 0C-H 0,4C-F 1,5C-Cl 1,0C-O 1,0C-N 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 Cl-Cl 2 Cl• unpaired electron
• Compounds with unpaired electronsare called free radicals and are very reactive• Cl-Cl 2 Cl• homolytic fission• A-B A+ + B- heterolytic fission
UV
UV
The reaction of methane and chlorine by radical reactions
1. 2 Cl• + CH4 CH3Cl + HCl
2. 2 Cl• + CH3Cl CH2Cl2 +HCl
3. 2 Cl• + CH2Cl2 CHCl3 + HCl
4. 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 H2BrC-CH2Br Spontaneous at NTP
colourless red/brown 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: 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-CH2-H2C-CH2Cl
UV
TerminationTwo radicals meet and a bond is formed. R-CH2• + R’-CH2• R-CH2-CH2-R’
• The polymer is ready!
Addition polymerisation reactions (I)
**
n
**
n
Cl
Cl
**
n
High pressuren
Ethene monomer Repeating unit of polyethene, PE
n
Chloroethene monomer Repeating unit of polychloroethene (polyvinylchloride, PVC)
n
Propene monomer Repeating unit of polypropene (PP)
Addition polymerisation reactions (II)
**
n
**
F F
FF
n
F
F
F
F
n
Phenylethene monomer Repeating unit of polyphenylethene (polystyrene, PS)
n
Tetrafluorethene monomer Repeating unit of polytetrafluorethene (PTFE) 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 alcoholIsopropanol, used as windscreen de-icer
Butanol • CH3-CH2-CH2-CH2-OH
1-butanol or butan-1-olNon-water soluble
• CH3-CCH3OH-CH3
2-metyl-2-propanol or 2-metylpropan-2-ol, a tertiary alcoholWater soluble
CombustionAlcohol + 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 Carboxylic acid
CH4 CH3OH HCHO H-COOH CO2
Methane Methanol Methanal Methanoic Carbon acid
dioxide
The more bonds to oxygen, the higher oxidation state of a carbon
C H
H
H
H
C OH
H
H
H
C HH
O
C OHH
O
C
O
O
Oxidation of alcohols
• Primary alcohol Aldehyde Carboxylic acid• Secondary alcohol Ketone• Tertiary alcohol no oxidation (unless C-C-
bonds are broken)
K2Cr2O7, Potassium dichromate, a common oxidizing agent
CH3CH2OH + Cr2O72- + H+ CH3CHO CH3COOH + Cr3+ + H2O
Reactive. Stable. Distill of Reflux
when formed
C OH
H
H
C
H
H
H
C H
O
C
H
H
H
C OH
O
C
H
H
H
Other oxidizing agents KMnO4, CuO, CuSO4
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 water-
soluble etc.• Acidic reactions• Methanoic acid H-COOH• Ethanoic acid CH3-COOH• Formed by strong oxidation of primary alcohols
• Salt form: -COO- or• Name: stem + suffix: -oate ion• Methanoate H-COO-
• Ethanoate CH3-COO-
• Formed by reaction of carboxylic acid and base:
NaOH + CH3COOH Na+ + CH3COO-
Salt of Carboxylic acids
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 HalogenoalkanesReactions
C—X d+ d-
=> Iodine compounds most reactive
Bond enthalpy kJ/mol
484 338 276 238
Bond in CH3-CH2-X
C-F C-Cl C-Br C-I
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
Heterolytic fission
Mechanism for SN1-reaction
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