Nomenclature & Introduction of Major Families of Organic Compounds

1. Nomenclature & Introduction of Major Families of Organic Compounds

2. Classification of Hydrocarbons alkadienes, etc. cycloalkadienes, etc. Huckel rule

3. 1. Hydrocarbons Organic compounds containing carbon and hydrogen only.

4. (a) Alkanes (CnH2n+2) Alkanes are hydrocarbons that contain only C – C and C – H single bonds(except CH4) Relatively inert as the  bonds are strong  saturated hydrocarbons contain the maximum possible number of hydrogen atoms per molecule

5. The first 10 members of the unbranched (acyclic) alkane series are : CH4Methane C6H14Hexane C2H6 Ethane C7H16Heptane C3H8 Propane C8H18Octane C4H10 Butane C9H20Nonane C5H12Pentane C10H22Decane

6. Cycloalkanes are alkanes in which all or some of the carbon atoms are arranged in a ring

7. Most stable due to less angle strain Cycloalkanes in skeletal forms Angle strain arises from repulsions between adjacent bond pairs

8. Cycloalkanes in skeletal forms

9. Alkanes and Cycloalkanes • General formula of acyclic alkanes: CnH2n+2 • General formula of cycloalkanes: Q.1 CnH2n

10. Methane (CH4) Ethane (CH3CH3) Propane(CH3CH2CH3) The First Three Members of Alkanes

11. Starting from C4H10, two or more structures are possible for the same molecular formula. This phenomenon is called isomerism. The different structures with the same molecular formula are called isomers.

12. Q.2 C4H10 All carbon atoms are sp3 hybridized - zigzag

13. Q.2 C5H12

14. Q.2 C6H14

15. Nomenclature of Alkanes IUPAC Conventions

16. Straight-Chain Alkanes

17. Branched-Chain Alkanes • Name the longest possible straight chain  give the parent name for the alkane

18. Branched-Chain Alkanes • Name the substituent groups – the branches CnH2n+1– Alkyl groups (derived from alkanes) CH3 – methyl C2H5 – ethyl

19. propyl isopropyl C3H7 –

20. sec-butyl secondary, 2 carbon butyl tert-butyl tertiary, 3 carbon isobutyl C4H9 –

21. 3. Number the positions of the substituent groups with the smallest possible numbers 2 2-methyl 2-methylbutane

22. If more than one substituent group of the same kind exist, the numbers are denoted by prefixes. 2  di 3  tri 4  tetra 5  penta 6  hexa

23. tetramethyl tetramethylmethane

24. 2 propane 2,2-dimethylpropane

25. 5 1 1,5,5-trichloro 1,5,5-trichlorohexane

26. 6 2 5 1   1,5,5-trichloro 2,2,6-trichloro ‘Lowest numbers’ does NOT refer to the smallest sum

27. 3 2 prefix is not considered • If two or more different substituent groups exist, they are named in alphabetical order but NOT in numerical order of their positions. 2,2-dimethyl 3-ethyl 3-ethyl-2,2-dimethylpentane

28. 3   tert-butyl 3-ethyl-2,2-dimethylpentane 3-tert-butylpentane

29. (b) Alkenes (CnH2n) One C=C double bond More reactive than alkanes due to weaker  bond  unsaturated hydrocarbons NOT contain the maximum possible number of hydrogen atoms per molecule

30. cyclopropene cyclobutene (b) Alkenes (CnH2n) First member is ethene (ethylene) Cyclic structures are possible

31. cyclopentene cyclohexene (b) Alkenes (CnH2n) First member is ethene (ethylene) Cyclic structures are possible Q.3 CnH2n-2

32. Starting from C4H8, isomerism occurs Structural isomerism : • same molecular formula • different linking orders of atoms

33. Chain isomerism Position isomerism Functional group isomerism Different carbon skeletons Functional groups in different positions Structural isomerism Different functional groups

34. Geometrical isomerism Optical isomerism Same linking order of atoms Stereoisomerism Different spatial arrangements of atoms

35. Geometrical Isomerism e.g.cis-but-2-ene and trans-but-2-ene

36. Both substituent groups are on the same side w.r.t. the axis of the C=C double bond Both substituent groups are on the opposite sides w.r.t. the axis of the C=C double bond

37. cannot be inter-converted at lower temperatures

38. maximum overlap of pz orbitals minimum overlap of pz orbitals Rotation about the axis of a double bond through an angle of 90o results in the breaking of the π bond

39. Geometrical Isomerism Arises from restricted rotation about the axis of the C=C double bond.

40. trans cis Position isomers Q.4 Chain isomerism position isomers Geometrical isomers

41. Position isomers Chain isomerism Q.4

42. Q.4 Functional group isomerism

43. Chain isomerism Q.4 A total of 11 isomers

44. C5H8 Q.4 C5H6

45. 1 pent-1-ene 2 pent-2-ene

46. 2 pent-2-ene (2E)-pent-2-ene trans Geometrical Isomerism cis (2Z)-pent-2-ene

47. E/Z notation If there are three or four different groups attached to the C atoms of C=C double bond E/Znotation rather than the cis/trans notation is used to name the stereoisomers of a molecule. E : in opposition to  trans Z : together  cis http://en.wikipedia.org/wiki/Cahn-Ingold-Prelog_priority_rule

48. 3 2 (2Z)-3-methylpent-2-ene 1 3 2 (2E)-3-methylpent-2-ene 1

49. 1 3 Q.4 2-methylbut-1-ene 2 1 2-methylbut-2-ene 2 3-methylbut-1-ene Functional group has a higher priority than branches

50. Q.4 cyclopentane methylcyclobutane