Homologous Series. Learning Outcomes :

Transcription

1 omologous Series N5 Learning Outcomes : Revision of homologous series including alkanes, alkenes, cycloalkanes, amines Reactions of alkenes including halogenoalkanes Systematic naming of hydrocarbons, including branched hydrocarbons.

2 ompounds in the same homologous series:- have a similar structure (functional group) fit a general formula have similar properties undergo the same reactions

3 omologous series Examples of homologous groups include: omologous series General formula Functional group Alkanes n 2n + 2 Alkenes n 2n = Alkynes n 2n - 2 = Alkanols n 2n + 1 O R O Alkanoic acids n 2n + 1 OO R OO Alkanals n 2n + 1 O R O

4 Alkanes General formula n 2n+2 Name Meth Eth Prop But Pent ex ept Oct No. s

5 Alkanes Full Structural formula Shortened structural formula 3 8 Molecular formula

6 Alkanes N5

7 Alkanes Alkanes contain only single carbon to carbon bonds they are described as saturated hydrocarbons. Alkanes are not very reactive (they do not react with acids, alkalis or bromine water). They do burn making them important fuels ½ O 2 2 O O = kj mol -1

8 Structural Isomers Isomers are compounds with the same molecular formula but different structural formulae. 3 butane 2-methylpropane ere, you can see that 2-methylpropane has a side chain.

9 Isomers or not isomers? Take care, the same molecule can be represented in different ways by: Drawing the branch below instead of above the carbon chain. Drawing the branch at the other end of the chain. By drawing a bend in the longest chain.

10 Isomers: Boiling points Use your understanding of structure and bonding to explain why the boiling point is increasing?

11 Isomers: Boiling points As the amount of branching increases, the tendency is for the boiling point to decrease. The structure is more compact, smaller surface area, weaker London's dispersion forces.

12 Naming ompounds of arbon Alkanes 1. Identify the longest chain 2. Identify the branches and name them. 3. Number the carbon atoms on the longest chain, at the end giving the lowest numbers for the branches. 4. Write the branches in alphabetical order. 5. If there are more branches with the same name use di, tri etc

13 N5 Naming Organic ompounds, Alkanes Worked examples

14 3 2-methylbutane

15 3 3 2,2-dimethylbutane

16 ethyl-3-methyldecane

17 Draw full structural formula for 2,3,3-trimethylpentane 3 3 3

18 ethyl-2,4-dimethylhexane

19 Problems for you to try: 1. Draw the shortened structural formulae of a) 2,4-dimethylhexane b) 4-ethyl-3-methyloctane c) 2,2,4,4-tetramethylpentane 2. Work out the systematic names of the following compounds. a) b) c)

20 ycloalkanes N5

21 ycloalkanes: have a ring structure and are saturated (contain only single bonds). Name yclopropane yclobutane yclopentane yclohexane ycloalkane Molecular Formula n 2n Structural Formula ( 2 ) n

22 Branched ycloalkanes methylcyclopentane 1,4-dimethylcyclohexane 1,2-dimethylcyclohexane

23 Alkenes N5

24 Alkenes Alkenes are hydrocarbons with the general formula n 2n Name No s Eth Prop But Pent ex ept Oct

25 Alkenes = 3 2 Full Structural formula Shortened structural formula 3 6 Molecular formula

26 Alkenes Alkenes contain a carbon to carbon double bond they are described as unsaturated hydrocarbons.

27 Structural Isomers Ethene has no isomers. Propene is isomeric with cyclopropene Isomers of alkenes can arise for two reasons the position of the double bond in the chain can vary the chain can be straight or branched

28 Naming ompounds of arbon Alkenes 1. Identify the longest chain, that contains a double bond. 2. Identify the branches and name them. 3. Number the carbon atoms on the longest chain, starting from the end nearest the double bond. 4. Pick the lowest number and give the position of the double bond. 4. Write the branches in alphabetical order. 5. If there are more branches with the same name use di, tri etc

29 N5 Naming Organic ompounds, Alkenes Worked examples

30 Naming Organic ompounds, Alkenes = but-1-ene

31 Draw full structural formula for but-2-ene =

32 = 3 4-methylpent-2-ene

33 2 5 = 3 3 5,5-dimethylhept-2-ene

34 Problems for you to try: 1. Draw the shortened structural formulae of a) oct-4-ene b) 3-ethylpent-1-ene c) 4,4-dimethylhex-2-ene 2. Work out the systematic names of the following compounds.

35 Reactions of Alkenes Addition reactions involving: ydrogen (ydrogenation) alogens ydrogen alides Water (ydration)

36 Addition Reactions of Alkenes ydrogenation, the reaction of an alkene with hydrogen is an example of an addition reaction. + - Propene Propane

37 Addition Reactions of Alkenes alogenation, the reaction with halogens is another example of an addition reaction Br Br + Br-Br orange/red colourless colourless propene 1,2-dibromopropane This can be used for a test for unsaturation

38 Reaction of Alkenes Reaction with ydrogen alides + -I Normally the from the halide attaches to the which already has the most hydrogen s. I or 2 -iodopropane I 1 -iodopropane

39 Alkenes with water oncentrated sulphuric acid reacts with ethene The reaction is an example of ydration. The overall effect of the acid is to combine water with ethene. At one time, this was the most important method for manufacturing ethanol from ethene. Nowadays, direct catalytic hydration of ethene is used. onc Phosphoric acid 2 = O 3 2 O Draw the full structural formulae for the hydration of ethene above.

40 Addition reactions

41 Naming alogenoalkanes Worked examples

42 Br Br 1,2-dibromoethane

43 Br Br 1,1-dibromoethane

44 3 3 l 3-chloro-2,2-dimethylpentane

45 alogen Derivatives (aloalkanes) alogenalkanes and halogenalkenes l 3 hloroform l 2 =l 2 l 2 F 2 Freon l 4 3 l 3 F 2 =F 2 orrecting fluid Gortex, Teflon l =l Solvent for grease Degreasing agent Paint Stripper Vinyl chloride Anesthetic

46 hlorofluorocarbons: F s All F s are very unreactive, are not flammable and not toxic. They are used as flame retardants. l 2 F 2 l 3 F The first refrigerant, and in aerosols. Used as a blowing agent to make expanded foam Recently hydrofluorocarbons have replaced some F s. e.g. 1,1,1,2-tetrafluoroethane is used as a refrigerant.

47 Ozone destruction O 3 F s are very stable, lasting for 100 years in the atmosphere. So over time, F s can reach the stratosphere. ere, UV radiation attacks the F s forming free radicals ( ). When UV light breaks bonds, free radicals are formed. Free radicals have unpaired electrons and, as a result, are highly reactive. U.V.light l 3 F l 2 F + l l + O 3 lo + O 2 lo + O l + O 2 Free radicals react with O 3, the reaction is complex, but one l free radical can catalyse the break down 1 million O 3 molecules. We will look at free radicals in more detail later in the unit!!!

48 Amines

49 Amines The structure of Amines is closely related to ammonia. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a carbon containing group Amines contain the Amino Functional Group. R Indicates any carbon groups.

50 Naming Amines Amines with small chains can be named with the carbon chains as branches. 3 N 2 Methylamine 3 2 N 2 Ethylamine 3 N 3 Dimethylamine 3 Larger chains use the prefix amino and the name of the alkane from which they are derived. N 3 N 2 3 Trimethylamine Pentane aminopentane

51 Amines Amines with low molecular mass are volatile gases and liquids. They resemble ammonia in having strong fishy smells. ethylamine trimethyl amine putrescine cadaverine 2 N( 2 ) 4 N 2 2 N( 2 ) 5 N 2 3,4-diaminobutane 1,5-diaminopentane

52 Reactions of Amines Amines are bases. Like ammonia they react with acids to form salts. N 3 + l N 4+ l - ammonia hydrochloric ammonium chloride acid 3 N 2 + l 3 N 3+ l - methylamine hydrochloric methylammonium chloride acid

53 Aromatics

54 Aromatic ydrocarbons Benzene is the simplest member of the class of aromatic hydrocarbons. 6 6 Benzene was originally thought to have the following structure. Kekulé suggested it contained alternating double and single bonds.

55 Aromatic compounds Although this structure was a good attempt in its time, there are serious problems with it: Benzene does not decolurise bromine water and does not undergo addition reactions. X ray analysis confirms all the bonds are the same length.

56 Aromatic compounds Although you will still come across the Kekulé structure for benzene, for most purposes we use the following structure. The hexagon shows the ring of six carbon atoms, each of which has one hydrogen attached. The circle represents a cloud of six delocalised electrons.

57 Aromatic compounds A benzene ring that has had a hydrogen removed is called a phenyl group Aromatic compounds are important feedstocks and are used in dyes, herbicides, insecticides fungicides, medicines and plastics

58 Aromatic compounds OO OO 3 NO 3 Aspirin 2-ethanoyloxybenzenecarboxcyclic acid O Paracetamol 4-hydroxyphenylethanamide

59 fe igher hemistry Unit 2: Natures hemistry Alcohols 24/01/2018

60 Alcohols Learning Outcomes : Give systematic names, structural formulae and isomers for branch chained alcohols. The structure of diols, triols and the effect of hydrogen bonding on properties of these molecules. lassification of alcohols as primary, secondary and tertiary.

61 Alcohols N5 omologous Series containing the hydroxyl (-O) functional group General formula: n 2n+1 O *Draw the full structural formula for: Methanol, 3 O Ethanol 2 5 O Propanol 3 7 O

62 Isomers * Draw the full structural formula of propanol* Straight chain isomers of Alkanols: Propanol has 2 isomers, propan-1-ol and propan-2-ol. O O propan-1-ol propan-2-ol

63 Practice Question Naming Alkanols O butan-1-ol

64 Practice Question Naming Alkanols 3 ( 2 ) 5 O 3 octan-2-ol

65 Practice Question Naming Alkanols ( 2 5 )O 3 3-ethylhexan-2-ol

66 Practice Question Naming Alkanols 3 O 3-methylbutan-1-ol

67 Other Alcohols ycloalcohols O yclohexanol Diols (dihydric) O O Ethan-1,2-diol (Anti freeze) Triols (trihydric) e.g. propan-1,2,3-triol or glycerol is used in cosmetics, paints and nitroglycerine explosives. *Draw the full structural formula for glycerol*

68 Ethanol 2 5 O O ydroxyl group R O δ - δ + δ + O δ - δ + Functional group -O ydrogen bonding allows ethanol to dissolve in water,( p 7. b.p. 78 o.) This effect decreases in alcohols as the length of the hydrocarbon chain increases. Ethanol is a good solvent, it behaves both like water and other hydrocarbon solvents.

69 Uses of Alcohols

70 Uses of Ethanol Solvents: In varnishes (as it evaporates easily), dyes, perfumes and drugs leaning products: Meths is ethanol with added methanol. Drinks: Ethanol is a natural product of fermentation. Ethanol cannot be more than 15% of the fermentation mixture, as ethanol is a poison and will kill the yeast. In the UK 8 g of ethanol is 1 UNIT.

71 Uses of ethanol Fuel: Increasingly seen as an important fuel. 3 2 O + 3 O 2 2 O O = kj mol -1 Ethanol can be used as a fuel in cars. Produced by fermentation e.g. sugar cane. It has an octane rating of 111. In Brazil about 20% of their petrol is ethanol

72 Uses of methanol Methanol again burns to form carbon dioxide and water. Methanol can be used as petrol additive or as a fuel in its own right. Octane rating of 114, also clean burning. Toxic and corrosive

73 lassification of Alcohols

74 lassification of Alkanols In alcohols the arbon attached to the O can be attached to 0, 1, 2 or 3 other arbon atoms 0 or 1 makes it primary as the O is on the end carbon 2 is secondary (the O is in the middle of a chain) 3 is tertiary (in the middle of a chain, opposite a branch) R 2 R 1 O R 3 R 1, R 2 and R 3 can represent ydrogens or any sized length of carbon chain, like a branch.they are referred to as alkyl groups

75 lassification of Alkanols O O O 3 primary secondary tertiary *Give the systematic name for each of the alcohols above*

76 Practice Question Problems for you to try: lassify the following as primary, secondary or tertiary alcohols: A O. B. O D.

77 ARBOXYLI AIDS Learning Outcomes : In this section you can learn about the characteristic chemical properties of the family of carboxylic acids, and find out how they are put to good use in everyday consumer products.

78 arboxylic Acids Vinegar s chemical name is ethanoic acid, sometimes called acetic acid. It is a member of a group of compounds called carboxylic acids, which contain the carboxyl functional group (-OO). If it is a straight chain hydrocarbon containing the carboxyl functional group it is known as an alkanoic or carboxylic acid.

79 arboxylic (Alkanoic) Acids They contain the ARBOXYL functional group OO They have the general formula n 2n+1 OO Because of the ability of lower molecular sized alkanoic acids to form hydrogen bonds, they are soluble in water. They have high b.p. s for the same reason. They also have a sharp smell. uman sweat contains a mixture of these compounds.

80 Testing arboxylic Acids ATIVITY: Testing carboxylic acids. Test a selection of carboxylic acids to for smell, p and reactivity. NOTES Show what functional group a carboxylic acid contains and what the members of the alkanoic acid homologous series look like by drawing the full structural formulae and chemical formulae for the first four members of the alkanoic acid homologous series. After completing the experiments make a note of your observations. In particular you should record any trends in smell, p and reactivity as the length of the carbon chain increases.

81 Reactions of arboxylic Acids ATIVITY: Neutralisation of carboxylic acids. Neutralise ethanoic acid using sodium hydroxide, using p paper to check it is no longer acidic. Evaporate off the water to leave the salt, sodium ethanoate. NOTES Write a note on the formation of salts from carboxylic acids. Write a word equation and a chemical equation for the formation of sodium ethanoate from the neutralisation of ethanoic acid and sodium hydroxide.

82 Naming Organic ompounds, Alkanoic acids O - O propanoic acid

83 Naming Organic ompounds, Alkanoic acids 3 3 O O - 3-methylpentanoic acid

84 Naming Organic ompounds, Alkanoic acids 3 O - 3 O 3,3-dimethylbutanoic acid

85 Naming Organic ompounds, Alkanoic acids 3 ( 2 ) 5 OO heptanoic acid

86 Alkanoic Acids Properties: Acids have a p below 7. Alkanoic acids are weak acids, so can react with some metals and alkalis. 2 3 OO + Mg ( 3 OO) 2 Mg + 2 Magnesium ethanoate 3 OO + NaO 3 OONa + 2 O Sodium ethanoate 3 OO + K 2 O OOK + 2 O + O 2 Potassium ethanoate

87 Uses of arboxylic Acids

88 Uses for arboxylic acids arboxylic acids are used in: some food items. Vinegar is dilute ethanoic acid. This is used in preparations for pickles, salads, sauces, etc. the manufacture of soaps. Sodium salts of fatty acids are used in soap and detergent industries. medicines. Ethanoic acid is used in making aspirin. industrial solvents. preparing perfumes and artificial essences used in food manufacturing. are produced in your sweat glands. Dogs can track humans by detecting the characteristic blend of these acids in your sweat.

89 Food preservation Vinegar has been used for millennia to preserve foods. There are many other foods where a proportion of ethanoic acid is added not only to enhance flavour, but also to help prevent food spoilage.

90 Removing lime-scale The ability of carboxylic acids to react with carbonates to form salts is exploited in some lime-scale removers. Lime-scale forms when hard water (water containing soluble calcium and magnesium salts) is boiled or allowed to evaporate. Under these conditions the soluble salts are changed into insoluble ones. For example, a water supply containing calcium hydrogen carbonate will deposit calcium carbonate when boiled. a(o 3 ) 2 (aq) ao 3 (s) + 2 O(l) + O 2 (g)