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Understanding Organic Compounds: Bonds, Homologous Series, and Functional Groups

This guide delves into the world of organic compounds, explaining fundamental concepts such as the electronic structure of carbon, bond formation, and the characteristics of homologous series. It highlights the organization of organic compounds into groups defined by functional groups, which determine their chemical behavior. The text includes details about alkanes, alkenes, alcohols, and carboxylic acids, alongside structural formulas and properties. A special focus is on how molecular size affects physical properties like boiling point and viscosity.

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Understanding Organic Compounds: Bonds, Homologous Series, and Functional Groups

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  1. Introduction • What is the meaning of the following phrases? • “Organic” chicken • Raised without the use of drugs, hormones or synthetic chemicals • Organic lifestyle • - simple, healthy and close to nature

  2. Bond Formation of Carbon Electronic structure of carbon is 1s22s22p2 Hence an atom of carbon has 4 valence electrons and it can form 4 covalent bonds by sharing electrons with 4 other atoms (H, O, N, S and halogens).

  3. Homologous Series Organic compounds are classified into families of compounds known as homologous series. A homologous series is a series in which each successive member increases by the unit -CH2- . Compounds in the same homologous series have the following properities: a. have the same general formula Eg. The general formula of alkane, a homologous series is CnH2n+2.

  4. Homologous series B Are different from the next member by a - -CH2 group.

  5. Homologous series c. Show a gradual change in physical properties. As the number of carbon atoms in the molecule increases, - melting and boiling points increase - viscosity (ability to flow) increases d. Can be prepared by similar methods e. Have similar chemical properties because they have the same functional group.

  6. Functional Group A functional group is any atom or group of atoms that gives the characteristic properties to a molecule and which defines the chemistry of an organic compound.

  7. Functional Group Name ending Homologous series Functional group Nil (contain only single bonds) -ane Alkane

  8. Name ending Homologous series Functional group -ene Alkene Functional Group Carbon - carbon double bond

  9. Name ending Homologous series Functional group -ol Alcohol Functional Group Hydroxyl group

  10. Name ending Homologous series Functional group -oic acid Carboxylic acid Functional Group Carboxyl group

  11. Name ending Homologous series Functional group -oate ester Functional Group Ester group

  12. Name ending Homologous series Functional group -amine amine Functional Group

  13. Identify all the functional groups

  14. Identify all the functional groups

  15. Classifying and Naming The naming of is divided into two parts: a) first part tells the chain length, which is the no. of carbon atoms. Name start with No. of carbon atoms Meth- 1 eth- 2 pro- 3

  16. Name start with No. of carbon atoms but- 4 5 6 Classifying and Naming Pent- Hex-

  17. 2 carbon atoms alkane 4 carbon atoms alcohol Classifying and Naming 2. Second part shows the homologous series. Ethane An alkane with 2 carbon atoms Butanol An alcohol with 4 carbon atoms

  18. Alkanes • saturated hydrocarbons • The general formula is CnH2n+2 • Hydrocarbons contain hydrogen and carbononly. • The names of alkanes end in -ane

  19. Alkanes Structural formula Physical state Name Molecular formula Gas Bp = -162°C CH4 methane

  20. Alkanes Structural formula Physical state Name Molecular formula Gas Bp = -89°C C2H6 ethane Condensed structural formula: CH3CH3

  21. Structural formula Physical state Name Molecular formula Gas Bp = -42°C propane Alkanes C3H8 Condensed structural formula: CH3CH2CH3

  22. Structural formula Physical state Name Molecular formula Gas Bp = -0.5°C Butane Alkanes C4H10 Condensed structural formula: CH3CH2CH2CH3

  23. Alkanes

  24. Alkanes (Page 3) Alkane with 5 carbon atoms = pentane Alkanes with 6 carbon atoms = hexane Alkanes with 7 carbon atoms = heptane

  25. Alkanes (Page 3) Alkane with 8 carbon atoms = octane Alkanes with 9 carbon atoms = nonane Alkanes with 10 carbon atoms = decane Alkanes are often described to be saturated, they contain only carbon-carbon single bonds and contain the maximum no. of H atoms per carbon.

  26. Properties of Alkanes (Pg 4) 1. Alkanes are covalent compounds. 2. They have low boiling points. Why? Alkanes are simple molecular compounds. The induced dipole-induced dipole forces between the molecules are weak and only a small amount of energy is needed to overcome these weak forces.

  27. Properties of Alkanes 3. As the no. of carbon atoms in a molecule increases, the boiling point becomes higher.

  28. Properties of Alkanes Alkanes are non-polar molecules. The intermolecular forces between the molecules are weak induced dipole-induced dipole forces . As the carbon chain gets longer, the no. of electrons increases, resulting in stronger induced dipole-induced dipole forces between the molecules, hence boiling point increases.

  29. Properties of Alkanes • 4. As the no. of carbon atoms in a molecule increases, the alkane become more viscous. • 5. As the no. of carbon atoms in a molecule increases, the alkanes becomes less flammable. • Alkanes are usually • insoluble in water • 7. Alkanes are usually less dense than water.

  30. Reactions of Alkanes • Alkanes are saturated and hence fairly unreactive. They undergo the following reactions: • Combustion • When combustion is complete, i.e., carried out in the presence of excess O2, alkanes burn to give carbon dioxide and water. • E.g combustion of butane – see white board • Alkanes are mostly used as • fuel as they produce energy when burnt. • Bottled gas which contains butane is used for cooking. Butane is also a fuel in cigarette lighter.

  31. Reactions of Alkanes When combustion is incomplete, i.e. the supply of O2 is inadequate, the products are carbon monoxide, soot and Water. Example 2CH4 (g) + 3O2 (g)  2CO (g) + 4H2O (g) CH4 (g) + O2 (g)  C (s) + 2H2O (g)

  32. Substitution with halogens Alkanes react with halogens in the presence of UV/sunlight . UV light is needed to start the reaction. It is used to break the covalent bonds in halogen molecule (E.g Cl2) to produce chlorine radicals. Cl-Cl  2Cl• The chlorine radicals are highly reactive and would attack the alkane molecule.

  33. Substitution with halogens Example – Substitution of methane with chlorine CH4 (g) + Cl2 (g)  CH3Cl (g) + HCl (g) Or equation showing full structural formula: See white board.

  34. Substitution with halogens

  35. Formation of crude oil

  36. Oil Rig

  37. Fractional Distillation of petroleum, Pg 9 • Petroleum or crude oil is a complex mixture of 150 hydrocarbon molecules. • Separation of petroleum into useful fractions is called refining, and it is done in oil refineries. • Refining consists of 3 basic steps: • 1. *Fractional distillation of petroleum • 2. *Cracking • 3. Reforming (Eg Converting straight-chain alkanes into branched-chain alkanes)

  38. 2nd step in Oil Refining

  39. 3rd step in Oil Refining b

  40. Oil Refineries in Singapore

  41. Fractional Distillation of Petroleum, Pg 10 • The different components in the crude oil have different boiling points and fractional distillation separates the components as a result of this property. • Each fraction consists of a mixture of hydrocarbon molecules that boils over a range of temperature.

  42. Fractional Distillation of Petroleum, Pg 9

  43. Fractional Distillation

  44. Cracking, Pg 10 A process in which involves splitting larger hydrocarbon molecules into smaller molecules by subjecting them to high temp and pressure, usually in the presence of a solid catalyst. Large hydrocarbons  short-chain alkanes + short-chain alkenes E.g C11H24  C2H4 + C9H20

  45. Cracking

  46. Thermal Cracking The alkanes are usually heated to a temperature between 500-800C.

  47. Catalytic Cracking On the industrial scale, cracking is done by passing the petroleum fraction containing long chains of carbon atoms over aluminium oxide or silicon (IV) oxide catalyst at a temperature of about 600C.

  48. Used to make plastics Uses of Cracking 1. The less useful large molecules are cracked to form smaller molecules like petrol as there is a greater demand for the smaller molecules. 2. Cracking is a way of making short-chain alkenes such as ethene or propene which are required to make plastics. C18H38 C6H14 + 6C2H4

  49. Uses of Cracking • Cracking produces hydrogen as a by-product in oil refineries. The hydrogen can be used to make ammonia by Haber process. • Cracking tends to produce branched-chain rather than straight-chain alkanes, providing petrol with higher octane rating. • The petrol from the fractional distillation of petroleum contains a lot of straight-chain alkane, such as octane.

  50. Cracking in the laboratory, Pg 11 The broken pot which contains aluminum oxide and silicon (IV) oxide acts as a Catalyst.

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