1. Organic Chemistry: Introduction IB Topic 10

2. Fundamentals of Organic Chemistry Section 10.1

3. What is organic chemistry? Organic Chemistry The study of carbon, the compounds it makes and the reactions it undergoes. The study of carbon, the compounds it makes and the reactions it undergoes. Over 16 million carbon-containing compounds are known. Over 16 million carbon-containing compounds are known.

4. Carbon Carbon can form multiple bonds with other carbon and with atoms of other elements. Carbon can form multiple bonds with other carbon and with atoms of other elements. Carbon can make four bonds since it has 4 valence electrons and most often bonds to H, O, N and S. Carbon can make four bonds since it has 4 valence electrons and most often bonds to H, O, N and S. Because the C-C single bond and the C-H bond are strong, carbon compounds are stable. Because the C-C single bond and the C-H bond are strong, carbon compounds are stable. Carbon can form chains and rings. Carbon can form chains and rings.

5. Hydrocarbons Hydrocarbons are organic compounds that only contain carbon and hydrogen Hydrocarbons are organic compounds that only contain carbon and hydrogen Some types of hydrocarbons include Some types of hydrocarbons include  Alkanes  C n H 2n+2  Alkenes  C n H 2n  Alkynes  C n H 2n-2

6. Hydrocarbons Classified as: Saturated Saturated - all C-C single bonds Unsaturated Unsaturated - contain double or triple C-C bonds Aliphatic Aliphatic – straight chains with single C-C bonds Cyclic Cyclic – ring structures with single C-C bonds Aromatic arenes Aromatic – ring structures of alternating single and double C-C bonds (arenes)

7. Homologous Series A homologous series is a series of related compounds that have the same functional group. Homologous compounds… For example, differ from each other by a – CH 2 – unit (methylene group) Can all be represented by a general formula (alkanes – C n H 2n+2 ) Have similar chemical properties Have physical properties that vary in a regular manner as the number of carbon atoms present increases

8. Homologous series – Alkanes

9. # C Prefix Alkane (ane) C n H 2n+2 1meth CH 4 methane 2eth C2H6C2H6C2H6C2H6ethane 3prop 4but 5pent 6hex

10. Trends in Boiling Points What is the trend? AlkaneFormula Boiling Pt./ o C methane CH 4 -162.0 ethane C2H6C2H6C2H6C2H6-88.6 propane C3H8C3H8C3H8C3H8-42.2 butane C 4 H 10 -0.5

11. Trends in Boiling Points Intermolecular forces present: Intermolecular forces present: Simple alkanes, alkenes, alkynes → van der Waals’ forces (nonpolar) → lower b.p. Simple alkanes, alkenes, alkynes → van der Waals’ forces (nonpolar) → lower b.p. Aldehydes, ketones, esters & presence of halogens (polar) → dipole: dipole forces → slightly higher b.p. Aldehydes, ketones, esters & presence of halogens (polar) → dipole: dipole forces → slightly higher b.p. Alcohol, carboxylic acid & amine → hydrogen bonding (w/ O, N, F) → even higher b.p. Alcohol, carboxylic acid & amine → hydrogen bonding (w/ O, N, F) → even higher b.p.

12. Formulas Empirical Formula: Smallest whole number ratio of atoms in a formula Molecular Formula: Formula showing the actual numbers of atoms Molecular Formula Empirical Formula CH 4 C2H6C2H6C2H6C2H6 CH 3 C 6 H 12 O 6 C4H8C4H8C4H8C4H8 C 8 H 16

13. Formulas Structural Formula Bond angles are drawn as though 90 o. The true shape around C with 4 single bonds is tetrahedral and the angle is 109.5 o. Show every atom and every bond. Can use condensed structural formulas. Hexane: CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 (condensed s.f.) M.F. = C 6 H 14 E.F. = C 3 H 7

14. Writing structural formulae Write the condensed structural formula for the following two compounds. For branches, write them in parantheses with the C they branch from.

15. Isomers Isomers: different compounds that have the same molecular formula Structural isomers: an isomer in which the atoms are joined in a different order so that they have different structural formulae Three kinds: chain isomers, positional isomers, functional group isomers Warning! Some molecules may seem like isomers, but there is free movement around C-C single bonds; they can rotate.

16. Isomers Chain isomers: branches are placed in different spots on the C-C backbone

17. Isomers Positional isomers: important functional groups are moved around on the C-C backbone, but the backbone does not change

18. Isomers Functional group isomers: certain atoms are rearranged on the C-C backbone to form different functional groups

19. Drawing structural formulae Draw out the structural formulas and write the condensed formula for all isomers that can be formed by: CH 4 C 2 H 6 C 3 H 8 C 4 H 10

20. Naming compounds 1.Determine the longest carbon chain 2.Use the prefix to denote the number carbons in the chain 3.Use the suffix “-ane” to indicate that the substance is an alkane 4.If the chain is branched, the name of the side chain will be written before the main chain and will end with “–yl”

21. Naming compounds Methylpropane Methylbutane Dimethylbutane

22. Naming compounds 1Meth-6Hex- 2Eth-7Hept- 3Prop-8Oct- 4But-9Non- 5Pent-10Dec-

23. longer than 4 carbons For chains longer than 4 carbons with side chains: 5.Number the carbons in the chain consecutively, starting at the end nearest side chains. 6.Designate the location of each substituent group by an appropriate number and name. 2 or more side chains And with 2 or more side chains: 5.Use prefixes di-, tri-, tetra-, to indicate when there are multiple side chains of the same type. 6.Use commas to separate numbers and hyphens to separate numbers or letters. 7.Name the side chains in alphabetical order.

24. Alkenes have one (or more) carbon to carbon double bonds Suffix changes to “-ene” When there are 4 or more carbon atoms in a chain, the location of the double bond is indicated by a number. Begin counting the carbons closest to the end with the C=C bond Numbering the location of the double bond(s) takes precedence over the location of side chains 1-butene 2-butene 24 Naming compounds

25. Functional Groups (p. 243)

26. Naming Carbon Rings To name a molecule with a ring, follow the steps as previously described for branches and functional groups. The numbering of the base chain/ring begins at the functional group. Double/triple bonds start the ring, if present. For the base chain/ring, insert a “cyclo-” prefix before the Latin number prefix. Example:

27. Classifying molecules With reference to the carbon that is directly bonded to an alcohol or amine group or a halogen: Primary = carbon atom is only bonded to one other carbon Primary = carbon atom is only bonded to one other carbon Secondary = carbon atom is bonded to two other carbons Secondary = carbon atom is bonded to two other carbons Tertiary = carbon atom is bonded to three other carbons Tertiary = carbon atom is bonded to three other carbons

28. Aromatic Hydrocarbons Presence of a benzene ring. August Kekule proposed a structure with a ring of C with alternating single and double bonds. Unsymmetrical with different lengths of bonds. Experimentally, it was discovered that the bonds are, in fact, the same length (140 pm) Single bond – 154 pm; double bond – 134 pm Bond order of 1.5 Actually symmetrical!

29. Aromatic Hydrocarbons Delocalized electrons from the ½ bond – resonance!

30. Aromatic Hydrocarbons Benzene is uncharacteristically stable. When adding H to this molecule, you would expect the enthalpy to change 3 times that of adding H to cyclohexene, but it isn’t – it’s much less. This difference in energy (expected vs. actual) is known as resonance energy or delocalization energy.

31. Functional Group Chemistry Section 10.2

32. Alkanes Simplest hydrocarbons Low bond polarity Strong covalent bonds C-C (346 kJ mol -1 ) C-H (414 kJ mol -1 ) Relatively inert Important reactions: Combustion Halogenation

33. Combustion of Alkanes Used as fuels (propane, butane, octane, etc) for the large energy released Volatility decreases as the length of C-chain increases – short chains used as fuel Undergoes complete combustion in presence of excess O 2 to produce CO 2 and H 2 O.

34. Combustion of Alkanes Undergoes incomplete combustion in presence of limiting O 2 to produce CO and H 2 O. CO irreversibly binds hemoglobin the blood thus reducing its oxygen-carrying capacity. Suffocation results

35. Quick Question Deduce the balanced equations for the complete combustion of: 1.Propane 2.Pentane 3.Hexane

36. Types of Reactions Substitution: replacement of individual atoms with other single atoms or with a small group of atoms. Addition: two molecules are added together to produce a single molecule. Elimination: the removal of two substituents from the molecule.

37. Halogenation of Alkanes Halogenating alkanes increases reactivity. Free-radical substitution and elimination Free-radical refers to a species that is formed when a molecule undergoes homolytic fission: two electrons of a covalent bond are split evenly between two atoms resulting in two atoms with a single electron. Heterolytic fission: both electrons in the bond are transferred to one atom resulting in cation and anion

38. Halogenation of Alkanes Example: methane reacts with chlorine in the presence of UV light:

39. Halogenation of Alkanes 3 stages to free-radical substitution: 1.Initiation 2.Propagation 3.Termination

40. Halogenation of Alkanes Initiation: homolytic fission of the chlorine molecule in presence of UV light produces 2 free- radicals

41. Halogenation of Alkanes Propagation: first stage is reaction of methane and chlorine free-radical to produce methyl radical.

42. Halogenation of Alkanes Propagation: second stage is the reaction of methyl radical with chlorine to produce chloromethane and chlorine radical

43. Halogenation of Alkanes Termination: reduces the concentration of radicals. Radicals begin to react with other radicals.

44. Alkenes Unsaturated hydrocarbons – contain at least one C-C double bond. Double bond makes them more reactive than corresponding alkane Undergoes addition reactions. Test for unsaturation: bromine water Addition of alkene to bromine water adds Br to molecule, thus rendering it colorless.

45. Hydrogenation Addition of hydrogen Important in food industry – removing the double- bond increases melting point thus making a substance that is solid rather liquid at room temperature Partial hydrogenation of fats and oils can be harmful to health – saturated vs unsaturated fats.

46. Halogenation of Alkenes Electrophilic halogenation of symmetrical alkenes involves addition of elemental halogens resulting in dihalogenated alkane:

47. Halogenation of Alkenes Example: but-2-ene and bromine

48. Halogenation of Alkenes Addition of hydrogen halide, HX, to a symmetrical alkane results in mono-halogenated alkane:

49. Polymerization of Alkenes Plastics industry utilizes addition polymerization Reaction of many smaller monomers with a C=C linking together to form a polymer. Monomer ethane supplied by petrochemical industry undergoes addition polymerization to form polyethene. Any monomer with a C-C double bond can undergo polymerization wherever the double bond is located.

50. Polymerization of Alkenes

51. Alcohols Can undergo complete combustion reactions to form CO 2 and H 2 O.

52. Oxidation of Alcohols

53. Oxidation of Alcohols Oxidation of primary alcohols occurs in two steps. First step produces an aldehyde. Second step produces a carboxylic acid.

54. Oxidation of Alcohols Aldehydes can be recovered using distillation. Distillation involves the gentle evaporation of liquids utilizing the difference in boiling points. The gas is collected and cooled into a pure distillate.

55. Oxidation of Alcohols Oxidation of secondary alcohols produces a ketone.

56. Oxidation of Alcohols To get a carboxylic acid, the aldehyde has to remain in the solution with the oxidizing agent for a longer amount of time. Instead of distillation, a reflux column is used. Refluxing is a technique that involves the cyclic evaporation and condensation of a volatile reaction mixture, preserving the solvent as it is does not evaporate.

57. Condensation reaction of alcohol and carboxylic acid Esters are derived from carboxylic acids Applications include flavoring agents, medications, solvents, and explosives. Esterification – a reversible reaction that occurs when a carboxylic acid and an alcohol are heated in the presence of a catalyst (e.g. H 2 SO 4 )

58. Nucleophilic substitution A halogenoalkane can undergo other reactions. The polar carbon-halogen bond, C-X, creates an electron deficient carbon making it open to ‘attack’ by electron-rich species known as nucleophiles – species that contain a lone pair of electrons and sometimes a full negative charge.

59. Electrophilic substitution Benzene does not readily undergo addition reactions but will undergo electrophilic substitution reactions. Electrophiles – electron-poor substance capable of accepting an electron pair. The double-bond attracts the electrophile but the stability of benzene leads to substitution NOT addition (like with alkenes).

60. Nucleophilic substitution

61. Electrophilic substitution