Introduction to Organic Chemistry

1. Introduction to Organic Chemistry 21.1 What is Organic Chemistry? 21.2 The Unique Nature of Carbon 21.3 Classification of Organic Compounds 21.4 Factors Affecting the Physical Properties of Organic Compounds

2. Dr Seemal Jelani What is Organic Chemistry?

3. Dr Seemal Jelani Organic Chemistry • Chemistry of the compounds present in living organisms. • They all contain carbon. • Organic Chemistry is the Chemistry of Carbon.

4. Dr Seemal Jelani A variety of organic products obtained from living things Natural Sources of Organic Compounds Carbohydrates / Proteins / Fats / Vitamins / Antibiotics Living things

5. Dr Seemal Jelani Fractional distillation / destructive distillation A variety of useful products derived from crude oil and coal Natural Sources of Organic Compounds Alkanes / Alkenes / Alkynes / Aromatic hydrocarbons Crude oil or coal

6. Destructive distillation Decomposition of a solid by heating it in a closed container and collecting the volatile constituents given off.

7. Dr Seemal Jelani Inorganic compounds Organic compounds obtained from living organisms obtained from non-living sources Development of Organic Chemistry as a Science In the past …, Chemistry

8. Dr Seemal Jelani Development of Organic Chemistry as a Science In 1828, Wohler (a German chemist) (Inorganic compound) (Organic compound)

9. Dr Seemal Jelani Development of Organic Chemistry as a Science Redefining … ... Organic chemistry is the study of carbon compounds (except CO,CO2, carbonates, hydrogencarbonates, carbides and cyanides) obtained from natural sources or synthesized in the laboratories.

10. Dr Seemal Jelani The Unique Nature of Carbon

11. Dr Seemal Jelani Carbon (ground state) Ability to form four strong covalent bonds • Electronic configuration of carbon (ground state) : 1s22s22p2

12. Dr seemal Jelani Hund’s Rule Every orbital in a sub shell is singly occupied one electron before any one orbital is doubly occupied All electrons in singly occupied orbitals have the same spin

13. Dr Seemal Jelani Carbon (excited state) 21.2 The Unique Nature of Carbon (SB p.5) Ability to form four strong covalent bonds • Each carbon atom has four unpaired electrons when excited • Tend to form four strong covalent bonds

14. Dr Seemal Jelani 21.2 The Unique Nature of Carbon (SB p.5) Ability to Catenate • Carbon atoms link together to form chains of varying length, branched chains and rings of different sizes • Catenation: •  Ability of atoms in forming stable bonds with itself, hence joining up into chains or rings

15. Dr Seemal Jelani 21.2 The Unique Nature of Carbon (SB p.5) Ability to Catenate C – C > Si – Si > Ge – Ge > Sn – Sn Bond strength  as bond length  Decrease as bond length increase C – C > N – N > O – O Bond strength  (decrease) as the number of lone pairs (increase)

16. Dr Seemal Jelani 21.2 The Unique Nature of Carbon (SB p.5) Ability to Catenate CnH2n+2 n = 1,2,3,…(no limit for n) SinH2n+2 n = 1 to 6 only  Silanes GenH2n+2 n = 1 to 3 only  Germanes SnnH2n+2 Only SnH4 (Stannane) exists

17. Dr Seemal Jelani 4 bonds sp2 sp3 sp 1 bond, 3 bonds 2 bonds, 2 bonds Carbon (excited state) 21.2 The Unique Nature of Carbon (SB p.5) Ability to Form Multiple Bonds

18. Dr Seemal Jelani 21.2 The Unique Nature of Carbon (SB p.6) * X = halogens

19. Dr Seemal Jelani Classification of Organic Compounds

20. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.7) Functional Groups • Organic compounds are classified by the the presence of characteristic functional groups.

21. Dr Seemal Jelani Functional Groups

22. Dr Seemal Jelani Functional Groups • Propane does not react with sodium • Ethanol and propan-1-ol react with sodium to give hydrogen gas

23. Dr Seemal Jelani and 21.3 Classification of Organic Compounds (SB p.7) Functional Groups • have similar chemical properties •  they contain the same functional group –OH •  they are classified into the same homologous series — alcohols

24. Dr Seemal Jelani CH4 C2H6 C3H8 C4H10 21.3 Classification of Organic Compounds (SB p.12) Homologous Series A homologous series is a series of compounds that have the same functional group, and each member differs from the next member by a – CH2 – unit in their formulae. CH2 CH2 CH2

25. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.12) The first four members of straight-chain alkanes

26. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.12) The first four members of straight-chain alcohols

27. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.13) Homologous Series • Members in the same series can be represented by a general formula. • e.g. alkanes: CnH2n+2 • alkenes: CnH2n • alkynes: CnH2n-2

28. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.13) Homologous Series • Members in the same series can be represented by a general formula. e.g. alkanols: CnH2n+1OH alkanals: CnH2n+1CHO alkanoic acids: CnH2n+1COOH

29. Dr Seemal Jelani Chemical properties 21.3 Classification of Organic Compounds (SB p.13) Homologous Series Functional group of an organic compound Members of a homologous series have similar chemical properties

30. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.13) Homologous Series • The physical properties change gradually along the homologous series • e.g. the longer the carbon chain in the molecule ( or the greater the molecular mass) • the greater the attractive force between molecules •  the higher the melting point, boiling point and density

31. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.13) Some physical properties of the first 20 members of straight-chain alkanes

32. Dr Seemal Jelani 21.3 Classification of Organic Compounds (SB p.13) Some physical properties of the first 20 members of straight-chain alkanes

33. Dr Seemal Jelani Factors Affecting the Physical Properties of Organic Compounds

34. Dr Seemal Jelani Main Factors Affecting the Physical Properties of Organic Compounds 1. Structure of the functional group 1.1 Dipole moment of the molecule 1.2 Formation of hydrogen bonding 2. Length of carbon chains (London dispersion forces)

35. Dr Seemal Jelani Structure of Functional Group • Molecules having a polar functional group have a higher b.p.than others with a non-polar functional group of similar molecular masses •  Stronger intermolecular attraction among molecules

36. Dr Seemal Jelani Structure of Functional Group

37. Dr Seemal Jelani Dipole Moment of Molecule • Tetrachloromethane has 4 polar bonds in the molecule • M.p. and b.p. are very low •  the molecule is non-polar •  the molecule is tetrahedrally symmetrical •  the dipole moments of the C  Cl bond cancel each other

38. Dr Seemal Jelani Examples of Polar Molecules with Net Dipole Moment Electronegativity

39. Dr Seemal Jelani Examples of Non-polar Molecules with No Net Dipole Moment

40. Dr Seemal Jelani Let's Think 2 Solubility of Organic Molecules • Depends on the polarity of organic molecules and the solvent • Non-polar or weakly polar compoundsdissolve readily in non-polar or weakly polar solvents • Highly polar compounds dissolve readily in highly polar solvents • “Like dissolves like”

41. Dr Seemal Jelani Hexane in tetrachloromethane Hexane in water Solubility of Organic Molecules

42. Dr Seemal Jelani Intermolecular forces between hexane and Tetrachloromethane molecules Intermolecular forces among hexane molecules and those among Tetrachloromethane molecules  Why does Hexane Dissolve Readily in Tetrachloromethane?

43. Dr Seemal Jelani Why is Hexane Insoluble in Water?

44. Dr Seemal Jelani Formation of Hydrogen Bonding • Molecules having OH or  NH2 groups are able to form hydrogen bonds • Hydrogen bonds affect the physical properties of alcohols and amines with low molecular masses

45. Dr Seemal Jelani Why does Propan-1-ol have a Higher Boiling Point?

46. Dr Seemal Jelani Formation of Hydrogen Bonding • Also affect the solubility of a molecule • Molecules with OH groups are able to form hydrogen bonds with surrounding water molecules •  Soluble in water

47. Dr Seemal Jelani Length of Carbon Chains • Molecules with higher molecular masses have higher m.p., b.p. and density •  Higher molecular masses •  Large molecular sizes •  Stronger London dispersion forces among molecules

48. Dr Seemal Jelani Length of Carbon Chains • Molecules with branched chains •  b.p. and densitylower than its straight-chain isomer • Straight-chain isomers have greater surface area in contact with each other  Greater attractive force among the molecules

49. Dr Seemal Jelani Length of Carbon Chains • Molecules with branched chains •  m.p.higher than its straight-chain isomer • Branched-chain isomers are more spherical  Packed more efficiently in solid state  Extra energy is needed to break down the efficient packing

50. Dr Seemal Jelani R = CnH2n+1 –