topic 10 organic chemistry inorganic chemistry? chemistry of life (now biochemistry) carbon...

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