Fuels & Heats of Organic Chemistry Reactions

1. Chpt. 21:Fuels & Heats of Reactions (Organic Chemistry)

2. Originally Organic Chemistry was the branch of chemistry concerned with substances that derived from living organisms i.e. plants and animals as it was thought that they were different from those extracted from minerals and other non-living sources – inorganic compounds. Examples of organic compounds: sugar, methane, vegetable dyes etc. Examples of inorganic compounds: water, sulphuric acid, calcium hydroxide etc. However, in 1828 Friedrich Wohler discovered that urea could be synthesised in the laboratory. This led to the redefinition of Organic Chemistry.

3. Definition: • Organic Chemistry: is defined as a study of the compounds of carbon. • carbon is unique among the elements in that it can • form stable chains and rings of carbon atoms. • This means there are millions of organic • compounds with thousands more being synthesised • every year. • Don’t Worry!!!!! Even though there are millions of • organic compounds the study of organic chemistry • is in fact very systematic and INTERESTING!!!!

4. Let the FUN Begin!!!

5. Hydrocarbons • Definition: • Hydrocarbon: is a compound that contains only hydrogen and carbon. • common sources of hydrocarbons – coal, natural • gas (methane), petroleum (crude oil) – formed in • the earth over millions of years. • preparation of methane (CH4) – methane can be • made readily by using material of plant or animal • origin. For example if manure is allowed to decay • under anaerobic conditions then bacteria will feed on • the manure causing it to decay and producing • methane. This gas is an excellent fuel and is used in • heating farms while the solid that remains is used as • a fertiliser.

6. Methane is produced naturally in slurry pits, coal • mines and refuse dumps – this is a huge hazard as • methane forms an explosive mixture with air • which has led to many accidents. Sir Humphry Davy had discovered that a flame enclosed inside a mesh of a certain fineness cannot ignite firedamp. The screen acts as a flame arrestor; air (and any firedamp present) can pass through the mesh freely enough to support combustion, but the holes are too fine to allow a flame to propagate through them and ignite any firedamp outside the mesh.

7. Methane is a gas that is contributing to • green house effect (this may be studied at a later • date)

8. Some Important Definitions • A Homologous Series is a family of compounds: • - with a uniform chemical type • - which show gradations in physical properties • - which have the same general formula • - which have a similar method of preparation • - with successive members differing by a CH2 unit • - which have similar chemical properties • Saturated Compounds: are compounds which contain • all single bonds only • Unsaturated Compounds: are compounds which • contain carbon-carbon double or triple bonds

9. Structural Formula: of a compound shows how the • atoms of a compound are arranged relative to each • other. • Structural Isomers: compounds which have the same • molecular formula but whose atoms are joined • together in a different order i.e. different structural • formula.

10. HYDROCARBONS Aliphatic Hydrocarbons Aromatic Hydrocarbons Alkanes Alkynes Alkenes

11. Aliphatic Hydrocarbons • Definition: • Aliphatic Hydrocarbons: an aliphatic compound is an organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties. • *Note: aliphatic compounds DO NOT contain benzene • ring • Aliphatic Hydrocarbons are classified under three main • groups: • - Alkanes • - Alkenes • - Alkynes Classification based on type of carbon-carbon bond in the molecules

12. The Alkanes • The alkanes form a family of hydrocarbons • (homologous series) of general formula CnH2n+2 • All the atoms are linked by single bonds thus the • alkanes are said to be saturated compounds (single C-C • bonds)

13. The Alkanes *Note: Add a CH2 to get the next member

15. *Note: Structural formulas do not show actual shape of molecules i.e. molecules are drawn as flat. In reality, each carbon atom has a tetrahedral structure Structural formulas drawn on paper simply represent how the atoms are bonded to each other.

16. Structural Isomers Remember: Structural Isomers: compounds which have the same molecular formula but whose atoms are joined together in a different order i.e. different structural formula. * Note: Only need to know the structures of the isomers of C4H10 (Butane) and C5 H12 (Pentane)

17. Isomers of Butane Butane Take Diagram

18. Isomers of Butane 2-methylpropane Take Diagram

19. Isomers of Butane Butane and 2-methylpropane have the same molecular formula C4H10. However, they are two different compounds with different physical properties e.g. different boiling points

20. Isomers of Pentane Pentane Take Diagram

21. Isomers of Pentane Take Diagram

22. Isomers of Pentane 2,2-dimethylpropane Take Diagram

23. *Note: You must know the formulae and structures of the alkanes up to C8 and the isomers up to C5

24. Alkyl Radicals • Definition: • When a hydrogen atom is missing from an alkane • molecule, the group of atoms which remains is • called an alkyl radical • The first four alkyl radicals:

25. Alkyl Radicals *Note: If two identical alkyl groups are present in a molecule, this is indicated using the prefix di- e.g. dimethyl = 2 methyl groups diethyl = 2 ethyl groups Side Chains (Substituent Groups/Branches): are groups of atoms attached to the main carbon chain

26. Naming Alkanes Step 1: Identify the longest continuous chain of carbon atoms This chain represents the parent alkane which is the basis of the name of the compound Step 2: The carbon atoms in this chain are then numbered from whichever end gives the lowest numbers to the atoms which have groups attached

27. Step 3: Indicate the type and position of the substituents Step 4: Name the compound i.e. put all the information together *Note: In naming compounds always: - put numbers before letters - put in alphabetical order

28. Examples of how to name alkanes will be completed on board please leave space!!!

29. Naming alkanes when given condensed structural formula: Example 1: Name the compound CH3CH2CH2CH(CH3)CH3 1) Draw out full structural formula - The brackets indicate branches or side chains - The remaining carbons form the longest continuous chain 2) Name compound as before

30. Naming Alkanes: Please complete exercise 21.1 parts (a),(c) and (d) pg 337

31. Important Alkanes and their Structure The following alkanes and their structure are very important due to their use as fuels. A.) 2,2,4 – trimethylpentane (iso-octane) an isomer of octane Take Diagram

32. B) Cyclohexane – hydrocarbon in which the carbons are arranged in a ring Take Diagram

33. In cyclohexane the bond angles are the tetrahedral bond angles of 109o. The bonds can be moved around to give two shapes a ‘boat’ and a ‘chair’!!! Do Not Take Slide

34. Drawing Structural Formulas You may be given the name of a compound and asked to draw its structural formula. Step 1: Analyse the name and pick out the parent alkane Step 2: Draw the carbon atoms in the longest chain and number them (order does not matter) Step 3: By analysis of the name you can determine the various side chains present, add these side chains to the carbon chain in the correct positions Step 4: complete the structural formula by filling in the remaining bonds with hydrogen atoms

35. Examples of how to draw structural formulas will be completed on board please leave space!!!

36. Drawing Alkanes: Please complete exercise 21.2 pg 337

37. Physical Properties of Alkanes • Appearance: • C1 - C4alkanes are colourless gases • C5 - C15alkanes are colourless liquids • C16 - upwards are colourless or white waxy solids • All alkanes are insolublein water i.e. they are non- • polar. • All alkanes have no smell • Their main use is as fuels e.g. methane is the main • component of natural gas. • All alkanes be represented by the formula: • CnH2n + 2

38. The Alkenes • The alkenes are the second homologous series of • hydrocarbons. They have the general formula CnH2n • Alkenes contain a carbon-carbon double bond (-C=C-) • and for this reason are said to be unsaturated • compounds.

39. The Alkenes • *Note: • - named from corresponding alkanes change the ending from –ane to –ene • - only need to know structures of first 3 alkenes

40. Structural Isomers • Note: Only need to know the structure of the isomers of C4H8 (Butene) • There are 3 isomers of butene all with the same molecular formula but different structural formulas: • - but-1-ene • - but-2-ene • - 2-methylpropene

41. But-1-ene (C4H8) CH2=CHCH2CH3 Take Diagram

42. But-2-ene (C4H8) CH3CH=CHCH3 Take Diagram

43. 2-Methylpropene (C4H8) CH2=C(CH3)CH3 Take Diagram

44. *Note: You must know the formulae and structures of the alkenes up to C4 and the isomers up to C4

45. Naming of Alkenes *Rules are very similar to those for naming alkanes Step 1: Identify the longest continuous chain of carbon atoms containing the C=C double bond This chain represents the parent alkane. The compound is named by changing the – ane ending to – ene. Step 2: Number the carbon atoms in this chain by starting at the end nearest the C=C. The double bond is indicated by writing the no. of the carbon atom after which the double bond occurs in the middle of its name.

46. Step 3: Indicate the type and position of the substituents Step 4: Name the compound i.e. put all the information together Examples of how to name alkenes when given structural formula and condensed structural formula will be completed on board please leave space!!!

47. Please complete exercise 21.3 (a), (b), (d) pg. 337

48. Drawing Structural Formulas of Alkenes You may be given the name of a compound and asked to draw its structural formula. Step 1: Analyse the name and: a) decide how many C atoms b) ensure presence of C=C c) evaluate position of C=C Step 2: Draw the carbon atoms in the longest chain and number them w.r.t C=C Step 3: Determine side chains and positions on chain Step 4: complete the structural formula by filling in the remaining bonds with hydrogen atoms

49. Examples of how to draw structural formulas will be completed on board please leave space!!!

50. Important Alkenes and their Structure Similar to cyclohexane it is also possible to have the carbon atoms arranged in a ring with a C=C between two of the carbon atoms - Cyclohexene Take Diagram