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 (1s 2 2s 2 2p 2 ) 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 Carbon is often (almost always) covalently bonded Other common atoms is hydrogen, oxygen, nitrogen ….. Other common atoms is hydrogen, oxygen, nitrogen ….. Molecules can be long chains or ring form Molecules can be long chains or ring form Hydrocarbons: Compounds only containing carbon and hydrogen 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 –CH 2 - Similar chemical properties Gradation in physical properties, such as boiling point

NameMole- cular formula Structural formulaBoiling point ( o C) MethaneCH EthaneC2H6C2H6 CH 3 -CH PropaneC3H8C3H8 CH 3 -CH 2 -CH ButaneC 4 H 10 CH 3 -CH 2 -CH 2 -CH 3 - 0,5 PentaneC 5 H 12 CH 3 -CH 2 -CH 2 -CH 2 -CH 3 36 HexaneC 6 H 14 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 69 The first straight-chain alkanes, general formula C n H 2n+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: CH 3 -CH 2 -CH 2 -CH 3 Butane CH 3 -CH-(CH 3 )-CH 3 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-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 Methyl-group

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 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 C n H 2n+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 BondBond enthalpy kJ/mol BondBond enthalpy kJ/mol C-C348Si-Si226 C-H412Si-H318 Ge-Ge188 Sn-Sn151

Alkanes have low bond polarity and low reactivity BondDifference in electro- negativity C-C0 C-H0,4 C-F1,5 C-Cl1,0 C-O1,0 C-N0,5 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 O 2 ): C 8 H O 2 16 CO H 2 O Incomplete (not enough O 2 ): C 8 H O 2 C + CO +2 CO H 2 O

Reactivity Alkanes can react with radicals- eg. chlorine in UV-light Cl-Cl 2 Cl unpaired electron Compounds with unpaired electrons are called free radicals and are very reactive Cl-Cl 2 Cl homolytic fission A-B A + + B - heterolytic fission UV

The reaction of methane and chlorine by radical reactions 1.2 Cl + CH 4  CH 3 Cl + HCl 2.2 Cl + CH 3 Cl  CH 2 Cl 2 +HCl 3.2 Cl + CH 2 Cl 2  CHCl 3 + HCl 4.2 Cl + CHCl 3  CCl 4 + 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 C n H 2n Low m.p. and b.p. due to only van der Waal´s forces Often gases and liquids at room temperature

Ethene CH 2 =CH 2 Propene CH 3 -CH=CH 2 Butene CH 3 -CH 2 -CH=CH 2 1-Butene or But-1-ene CH 3 -CH 2 =CH-CH 3 2-Butene or But-2-ene Pentene CH 3 -CH 2 -CH 2 -CH=CH 2 1-Pentene or Pent-1-ene CH 3 -CH 2 -CH 2 =CH-CH 3 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 H 2 C=CH 2 + Br 2  H 2 BrC-CH 2 Br Spontaneous at NTP colourless red/brown colourless Used as proof of C-C-double bonds H 2 C=CH 2 + HCl  H 3 C-CH 2 Cl Spontaneous at NTP

Addition reactions with hydrogen and water H 2 C=CH 2 + H 2  H 3 C-CH 3 E.g. Ni-catalyst. Industrially important when transformation of vegetable oil to margarine H 2 C=CH 2 + H 2 O  H 3 C-CH 2 OH Catalyst: H 2 SO 4, H 3 PO 4 or Al 2 O 3 ~300 o C, 7 MPa. At 1 atm the reversed reaction is favoured. Synthesis of alcohols

Polymerisation reactions Alkenes forming plastics, making plastics Radical reactions involving Cl 2 and UV-light Initiation: Cl-Cl 2 Cl Propagation; adding monomers to a long chain, e.g. H 2 C=CH 2 + Cl  H 2 C-CH 2 Cl monomer H 2 C-CH 2 Cl + H 2 C=CH 2  H 2 C-CH 2 -H 2 C-CH 2 Cl H 2 C-CH 2 -H 2 C-CH 2 Cl + H 2 C=CH 2  H 2 C-CH 2 -H 2 C-CH 2 - H 2 C-CH 2 Cl UV

Termination Two radicals meet and a bond is formed. R-CH 2 + R’-CH 2  R-CH 2 -CH 2 -R’ The polymer is ready!

Addition polymerisation reactions (I)

Addition polymerisation reactions (II) 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 CH 3 OH Wood spirit, formed by pyrolysis of wood. Highly toxic! Ethanol CH 3 -CH 2 -OH Alcohol, formed during fermentation of sugar. Technically very important; In drinks, as a solvent, desinfectant and fuel

Propanol CH 3 -CH 2 -CH 2 -OH 1-propanol or propan-1-ol a primary alcohol CH 3 -CHOH-CH 3 2-propanol or propan-2-ol a secondary alcohol Isopropanol, used as windscreen de-icer

Butanol CH 3 -CH 2 -CH 2 -CH 2 -OH 1-butanol or butan-1-ol Non-water soluble CH 3 -CCH 3 OH-CH 3 2-metyl-2-propanol or 2-metylpropan-2-ol, a tertiary alcohol Water soluble

Combustion Alcohol + Oxygen  Carbon dioxide + water CH 3 -CH 2 -OH + 3 O 2  2 CO H 2 O

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 CH 4 CH 3 OH HCHO H-COOH CO 2 Methane Methanol Methanal Methanoic Carbon acid dioxide 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-C- bonds are broken)

K 2 Cr 2 O 7, Potassium dichromate, a common oxidizing agent CH 3 CH 2 OH + Cr 2 O H +  CH 3 CHO  CH 3 COOH + Cr 3+ + H 2 O Reactive. Stable. Distill of Reflux when formed Other oxidizing agents KMnO 4, CuO, CuSO 4

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 CH 3 -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) CH 3 -CO-CH 3 Pentane-2-one CH 3 -CO-CH 2 -CH 2 -CH 3 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 CH 3 -COOH Formed by strong oxidation of primary alcohols

Salt form: -COO - or Name: stem + suffix: -oate ion Methanoate H-COO - Ethanoate CH 3 -COO - Formed by reaction of carboxylic acid and base: NaOH + CH 3 COOH Na + + CH 3 COO - Salt of Carboxylic acids

Halogenoalkane Functional group: -X (-F, -Cl, -Br, -I) Name: e.g. prefix: Chloro- + alkane Chloromethane CH 3 -Cl Bromoethane CH 3 -CH 2 -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 –NH 2 H-bonds => higher bp’s, smaller ones are water-soluble etc. Name: stem + suffix: -ylamine (or prefix amino-) Ethylamine CH 3 -CH 2 -NH 2

10.5 Halogenoalkanes Reactions C—X  +  - => Iodine compounds most reactive Bond enthalpy kJ/mol Bond in CH 3 -CH 2 -X C-FC-ClC-BrC-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, H 2 O, - OH, - CN, NH 3 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 CH 3 -CH 2 -Cl (aq) + - OH (aq)  CH 3 -CH 2 -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 S N 1 and S N 2

SN2SN2 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.

S N 2 Mechanism Nucleophile attack Transition state Leaving group Bonds breaks and forms

Enthalpy diagram for S N 2 Enthalpy Reaction coordinate

SN1SN1 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 S N 1-reaction

Enthalpy diagram for S N 1-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 Cl 2 by UV-light. 4. Addition reaction. Hydrogen halide, spontaneous at STP 5. Addition reaction. H 2 and Ni-catalyst 6. Addition reaction. Halogene, spontaneous at STP 7. Poly-addition. Radical mechanism. Initiation, prolongation and termination 8. Substitution reaction with NaOH; S N 1 or S N 2 9. Oxidation of primary alcohol with acidified K 2 Cr 2 O 7. Distillation to get the product 10. Oxidation of primary alcohol with acidified K 2 Cr 2 O 7. Reflux to get the product 11. Oxidation of secondary alcohol with acidified K 2 Cr 2 O 7