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ORGANIC CHEMISTRY Part 2 Studying the properties of Organic Compounds Basic Terminologies Catenation: This is the ability of carbon atoms to form covalent.

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Presentation on theme: "ORGANIC CHEMISTRY Part 2 Studying the properties of Organic Compounds Basic Terminologies Catenation: This is the ability of carbon atoms to form covalent."— Presentation transcript:

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2 ORGANIC CHEMISTRY Part 2

3 Studying the properties of Organic Compounds Basic Terminologies Catenation: This is the ability of carbon atoms to form covalent bonds with itself to give long, straight, branched and closed chains Homologous series: This is a family of organic compounds, which have a regular structural pattern, similar chemical properties and in which each successive member differs by –CH 2 - or by atomic mass unit of 14. Examples : Alkanes, Alkenes, Alkynes, Alkanols, etc

4 Basic Terminologies Functional group: This is an atom, group of atoms (radical) or a bond common to a homologous series, and which determines their main chemical properties.

5 FUNCTIONAL GROUPS Continued:

6 Comparing organic compounds

7 Basic Terminologies Isomerism: This is the existence of two or more compounds with the same molecular formular but different structural formula. These compounds are called ISOMERS.

8 Structural isomerism Butan-1-ol Butan-2-ol C 4 H 10 O ethoxyethane butanol Positional isomerism

9 Drawing Structural Isomers of alkanes Two possible Isomers of Butane

10 Activity The compound C 5 H 12 has three isomers. Draw the structures of these three isomers. propane

11 MORE ISOMERISM IN ALKENES Draw all the possible isomers C 4 H 8

12 Activity Chlorine was reacted with Pentane in the presence of ultra violet radiation to produce C 5 H 11 Cl. Draw and name all the possible structures of the compound

13 3. Optical Isomers is the existence of two or more compounds with the same molecular formula but with different configurations and because of the molecular asymmetry they rotate plane polarized light. NB: They have a chiral carbon.[Chiral carbon is one that has four different substituents of its four covalent bonds.] These isomers are called enantiomers because they rotate plane polarized light. NB: If compounds rotate light to the right, it is called dextro rotatory while to the left is leavo rotatory

14 4. Geometrical isomerism Geometric isomers exist as Cis and Trans Isomers Groups attached to the alkene could be positioned on the same side of the alkene or on opposite sides of the alkene. Such compounds are different in chemical and physical properties as well as in their geometry, and are called geometrical isomers NB: Trans isomers of compounds are usually more stable than cis isomers Cis- but-2-ene Trans- but-2-ene

15 THE ALKANES The alkanes are aliphatic hydrocarbons with general molecular formular C n H 2n+2. They form homologous series of saturated hydrocarbons A saturated hydrocarbon or alkane is a hydrocarbon in which all of the carbon-carbon bonds are single bonds All Carbon atoms are sp 3 hybridized with bond angles 109.5 o

16 The alkane family

17 The physical properties of alkanes such as melting points, boiling points, densities etc. increase steadily due to increasing molar mass or increasing number of carbon atoms and van der Waal's force As the number of carbon atoms increases, the number of structural isomers increases rapidly. For example, butane, C 4 H 10 has two isomers and C 10 H 22, has 75 isomers! Physical properties of alkanes

18 Laboratory Preparation of Methane Methane is prepared by heating anhydrous sodium ethanoate with an equal mass of soda-lime. Soda-lime is used in preference to caustic soda, (NaOH) because: - it is not deliquescence - it does not attack glass. METHANE (CH4) CH 3 COONa (aq) + NaOH (aq) CH 4(g) + Na 2 CO 3(s)

19 Laboratory Preparation of Methane

20 Physical properties of methane - it is a colorless and odorless gas - it is less dense than air - it is slightly soluble in water - it is neutral to litmus

21 Chemical properties(Reactions) of Alkanes (1) Combustion with pale blue non-luminous flame In presence of excess air __ C 3 H 8 __ CO 2 + 45 The reaction is exothermic Note: Combustion with insufficient (limited supply of air O 2 ) __ C 3 H 8 + __ O 2  __ CO + __ H 2 O 3 4 7/2 Common residue from above reactions is carbon (coke) + __ O 2  __ H 2 O 3 The general equation for combustion of alkanes is: C x H y + (x+y/4)O 2 y/2H 2 O + xCO 2 ( x and y are number of carbon atoms and oxygen respectively.

22 2. Substitution Reactions: This is a characteristic reaction of alkanes where Chlorine is catalyzed by Ultra violet light. Mechanism of Chlorination A. Initiation : B. Propagation C. Termination

23 CH 4(g) + Cl 2(g) CH 3 Cl (g) + HCl (g) CH 3 Cl (g) + Cl 2(g) CH 2 Cl 2(g) + HCl (g) CH 2 Cl 2(g) + Cl 2(g) CHCl 3(g) + HCl (g) CHCl 3(g) + Cl 2(g) CCl 4 (g) + HCl(g) trichloromethane tetrachloromethane dichloromethane chloromethane UV Chlorination of methane is an example of substitution reaction: Note: Although alkanes undergo substitution reaction, they are generally inert.

24 Uses of methane: It is used as fuel either alone or mixed with other gases. It is used in production of water gas. It is used for making hydrogen, carbon black, carbon(IV) sulphide, etc. Trichloromethane is used formerly as an anaesthetic in surgical operations. Tetrachloromethane is a very useful organic solvents.

25 ALKENES The alkenes are unsaturated hydrocarbons that form homologous series with the general formula C n H 2n (n starts from 2, then 3,4,5,etc.). Alkenes are characterized by the presence of at least, a double bond between two adjacent carbon atoms this is why the are unsaturated. Alkenes are SP 2 hybridized.

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27 Dehydration of Ethanol Ethene is prepared by the action of heat on a mixture of ethanol and excess concentrated H 2 SO 4 at about 170 o C-180 o C C 2 H 5 OH C 2 H 4 + H 2 O Conc. H 2 SO 4 180 o C Laboratory Preparation of Ethene

28 Note: The empty flask is to prevent the NaOH from sucking back into the reaction mixture The sodium Hydroxide is used to remove gaseous impurities mainly carbon (IV) oxide and phosphine

29 Physical Properties of Ethene 1. it is a colorless gas with a faint sweetish smell. 2. it is only sparingly soluble 3. it is slightly less dense than air 4. it has no action on litmus

30 Chemical properties of Ethene Ethene, an unsaturated hydrocarbon, is very reactive due to its double bond. Ethene and other alkenes undergo the following reactions: - combustion reactions - addition reactions - oxidation and - polymerization

31 Chemical properties of Ethene

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33 Addition Reactions Ethene undergoes addition reactions at the double bonds in order to produce saturated compounds. (i). Hydrogenation: This is the addition of hydrogen to ethene in presence of finely divide Nickel as catalyst at 300 o C.

34 (ii). Halogenation: This is the addition of halogens such as F 2,Cl 2,Br 2 or I 2 When ethene is bubbled through bromine (reddish brown), the bromine is decolorized. This reaction is used as a test for unsaturation to distinguish unsaturated hydrocarbon from saturated hydrocarbon.

35 (iii).Addition of bromine water: When bromine water is added to ethene, there is immediate decolorization, due to formation of bromoethanol. CH 2 =CH 2 + HO-Br CH 2 (OH) – CH 2 Br This reaction is also used as a test for unsaturation to distinguish unsaturated hydrocarbon from saturated hydrocarbon.

36 (iv). Hydrohalogenation: This is the addition of hydrogen halides such as HF, HCl, HBr and HI to an alkene. Hydrogen Chloride adds to Ethene at room temperature to give Chloroethane. Addition of halide to unsymmetrical alkene e.g. propene gives two products but, one predominates.

37 The rule for writing the main product is known as Markovnikoff’s rule which states: In adding halides to unsymmetrical alkene, the hydrogen atom from the halide goes to the carbon atom that has more hydrogen atoms.

38 3. Oxidation reaction of ethene: When purple solution of acidified KMnO4 is added to ethene at room temperature, there is immediate decolorization. Ethene is oxidized to ethane-1,2-diol.

39 4. Polymerization reaction of Ethene: Molecules of ethene polymerizes at high temperature and pressure in the presence of catalysts to form polyethene (polythene)

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41 Activity

42 Uses of Ethene 1. - it is the main source of many important organic compounds. 2. - it is used to produce synthetic rubber. 3. - A derivative of ethene, 1,2-dibromoethene is used as petrol additive. 4. - it is used to hasten ripening of fruits. 5. Ethene is used as a raw material for plastic industries

43 ALKYNES (Acetylenes) The alkynes form the homologous series of unsaturated hydrocarbons with the general formula C n H 2n-2 (n = a whole number from 2, then, 3,4,5,etc.) The first member of the alkynes is ethyne, i.e. when n is 2. The alkynes must have at least one triple bond Alkynes are SP hybridized

44 Laboratory Preparation of Ethyne Ethyne is prepared in the laboratory by the action of cold water on calcium dicarbide, CaC 2 in a conical flask. The flask is placed on a sand. The sand prevents the heat generated from breaking the flask. As the cold water drips on the calcium dicarbide, there is effervescence. The colourless gas evolved is passed through CuSO 4 solution in dilute H 2 SO 4, to remove impurity phosphine(PH 3 ). The gas is then collected over water., CaC 2(g) + H 2 O (l) CaO (s) + C 2 H 2(g)

45 Laboratory preparation of ethyne

46 Physical Properties of Ethyne 1. Ethyne is a colourless gas with a characteristic sweet smell when pure. 2. It is only sparingly soluble in water 3. It is slightly less dense than air 4. It is unstable and may explode on compression.

47 Chemical Properties The alkynes are more unsaturated than the alkenes, hence are more reactive. 1. Combustion: Ethyne burns in oxygen with sooty luminous flame, due to the high carbon content, to produce carbon(IV) oxide and water vapour. 2C 2 H 2(g) + 5O 2(g) 4CO 2(g) + 2H 2 O (l)

48 2. Addition Reactions: Like ethene, ethyne undergoes addition reactions, usually in two stages. (i). Hydrogenation: Ethyne reacts with hydrogen in the presence of finely divided nickel at 200 o C to produce, first ethene and finally, ethane.

49 Addition Reactions: (ii). Halogenation: Ethyne adds to Cl 2, Br 2 or I 2 in the presence of finely divided iron to produce, first, dihalide, and then, a tetrahalide:

50 (iii). Hydrohalogenation: Addition of HBr to ethyne, gives monobromoethene, first, and finally, 1,1-dibromoethane (major),and 1,2-dibromoethane (minor). Addition Reactions:

51 (iv). Hydration of ethyne: When water is added to ethyne in the presence of (H 2 SO 4 /HgSO 4 ) at 60 o C, ethenol is formed first, which then rearranges to give ethanal. Addition Reactions:

52 3. Polymerization of ethyne Ethyne polymerizes to form aromatic hydrocarbon, Benzene, in the presence of complex organo-nickel catalyst 3C 2 H 2(g) C 6 H 6 EthyneBenzene Organo-nickel catalyst

53 4. Substitution reaction Ethyne, propyne and other terminal alkynes undergo substitution reactions when passed over ammoniacal solutions of copper(I)Chloride and Silver trioxonitrate (V) at room temperature to form precipitates. C 2 H 2(g) + 2CuCl (aq) CuC 2 + 2HCl C 2 H 2(g) + 2AgNO 3(aq) Ag 2 C 2 + 2HNO 3 This reaction is used to distinguish ethyne from ethene which does not form these metallic derivatives.

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55 Comparison between alkanes, alkenes and alkynes FEATUREALKANEALKENEALKYNE Degree of saturation SaturatedUnsaturatedHighly unsaturated Combustion Blue smokeYellow luminousSmoky flame General formula C n H 2n+2 C n H 2n C n H 2n-2 Unique/common reactions SubstitutionAdditionsAdditions(more reactive than alkenes) TEST FOR UNSATURATION Reaction with bromine solution in dark No reactions (Alkanes do not react in the dark) Decolourizes bromine solutions Decolorize bromine solutions Reaction with acidified KMnO 4 No reactionDecolourizes the solution Reaction with silver trioxonitrate No reaction Terminal alkynes form a white precipitate

56 Uses of Ethynes 1. Ethyne is sometimes used as fuel in lamps such as miners lamp. 2. Ethyne is mixed with oxygen to produce a very hot and easily controllable flame, oxy-ethyne, which is used for cutting and welding metals 3. Ethyne is a source of ethanal and other solvents which are used industrially for dry cleaning and dissolving grease

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