Organic Chemistry L11 PDF

Official (Closed) - Non Sensitive Organic chemistry Alkanes Alkenes Alcohols Carboxylic acids Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 1 Official (Closed) - Non Sens...

Official (Closed) - Non Sensitive Organic chemistry Alkanes Alkenes Alcohols Carboxylic acids Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 1 Official (Closed) - Non Sensitive Organic compounds Organic compounds are compounds that contain the element carbon. Can be: Naturally-occurring (e.g. proteins, glucose) Synthetic (e.g. plastics, detergents, medicines) Organic compounds that only contain hydrogen & carbon are called hydrocarbons. Organic compounds may also contain other elements such as oxygen, nitrogen, sulfur. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 2 Official (Closed) - Non Sensitive Homologous Series A homologous series is a family of organic compounds with the same functional group and similar chemical properties. Examples of homologous series: alkanes, alkenes, alcohols, carboxylic acids. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 3  Official (Closed) - Non Sensitive Functional groups A functional group is an atom or group of atoms that gives a molecule its characteristic properties. H H H H H H H C C C H H C C C H H H H H Alkanes Alkenes Alkanes do not have functional groups. Contain carbon-carbon double bond There are only C-C and C-H bonds. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 4 Official (Closed) - Non Sensitive Functional groups H H H O H C C O H H C C O H H H H Alcohols Carboxylic acids Contain the hydroxyl group Contain the carboxyl group Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 5 Official (Closed) - Non Sensitive Naming organic compounds The name of an organic compound is divided into 2 parts: The prefix tells us the number of carbon atoms in each molecule Prefix Meth- Eth- Prop- But- No. of C atoms 1 2 3 4 The suffix tells us which homologous series the compound belongs to Suffix -ane -ene -ol -oic acid Homologous series alkane alkene alcohol Carboxylic acid Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 6 Official (Closed) - Non Sensitive Example: prop ene eth ol H H H H C C C H H C C O H H H H H H propene ethanol Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 7  Official (Closed) - Non Sensitive Alkanes Alkanes are a homologous series of hydrocarbons that contain only carbon-carbon single covalent bonds.  they are saturated hydrocarbons. Alkanes have the general formula CnH2n+2, where n = number of carbon atoms Name No. of C atoms Molecular formula Methane 1 CH4 Each member of the homologous series Ethane 2 C 2H 6 differs from the next Propane 3 C 3H 8 by a –CH2- unit. Butane 4 C4H10 Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 8  Official (Closed) - Non Sensitive Structural formulae of alkanes Name Molecular formula Structural formula Ball-and-stick model Methane CH4 H H C H H Ethane C 2H 6 H H H C C H H H Propane C 3H 8 H H H H C C C H H H H Butane C4H10 H H H H H C C C C H H H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 9 Official (Closed) - Non Sensitive Try it yourself 1. For methane, draw the: a) Dot-and-cross diagram b) Structural formula Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 10 Official (Closed) - Non Sensitive Try it yourself 2. For ethane, provide the: a) Empirical formula b) Molecular formula c) Structural formula Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 11 Official (Closed) - Non Sensitive Isomerism in alkanes Isomers are compounds that have the same molecular formula but different structural formula. They have different physical properties (e.g. melting & boiling points) H E.g. H C H H H H H H H H C C C C H H C C C H H H H H H H H Butane Methylpropane Molecular formula C4H10 Molecular formula C4H10 Straight-chain Branched-chain Boiling point -0.5 °C Boiling point -11.7 °C Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 12 Official (Closed) - Non Sensitive Isomers of Pentane NEW Pentane, b.p. 36oC 2-methylbutane, b.p. 27.9oC b.p. – boiling point 2,2-dimethylpropane, b.p. 9.5oC Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 13 Official (Closed) - Non Sensitive Physical properties of alkanes Alkanes are covalent compounds with simple molecular structures. Therefore, alkanes: Have low melting and boiling points Are insoluble in water Are soluble in organic solvents Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 14 Official (Closed) - Non Sensitive Physical properties of alkanes As the sizes of the alkane molecules increase: 1. Their melting & boiling points increase As the sizes of the alkane molecules increase, the forces of attraction between the molecules also increase. Name Melting point/°C Boiling point/°C Physical state at r.t.p. Methane -182 -162 Gas Ethane -183 -89 Gas Propane -188 -42 Gas Butane -138 -0.5 Gas Pentane -130 36 Liquid Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 15 Official (Closed) - Non Sensitive Physical properties of alkanes 2. They become more viscous Due to the stronger forces of attraction between the alkane molecules 3. They become less flammable As the sizes of alkane molecules increase, the % of carbon in the alkane molecules also increases. As a result, alkanes become less flammable. They produce a smokier flame, due to incomplete combustion of alkane molecules. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 16 Official (Closed) - Non Sensitive Chemical properties of alkanes Generally unreactive The C-C and C-H bonds are strong and difficult to break. Can undergo combustion & substitution reactions. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 17 Official (Closed) - Non Sensitive Combustion When ignited by a spark or flame, alkanes burn readily in excess oxygen to produce carbon dioxide & water vapour Alkane + oxygen  carbon dioxide + water vapour E.g.: Methane + oxygen  carbon dioxide + water vapour CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g) Alkanes make good fuels. Methane is used in cooking gas. Petroleum fractions such as petroleum gas, kerosene & diesel contain alkanes. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 18  Official (Closed) - Non Sensitive Substitution reactions Alkanes react with halogens (e.g. chlorine, bromine) in the presence of UV light. E.g.: H H U V light H C H + Cl Cl H C Cl + H Cl H H An H atom in methane is substituted by a chlorine atom to form chloromethane. More H atoms can be replaced with Cl atoms to form other compounds such as dichloromethane, trichloromethane & tetrachloromethane. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 19 Official (Closed) - Non Sensitive Questions 1. Between C6H14 and C16H34, which hydrocarbon will give out more smoke when ignited? 2. On complete combustion, 1 mol of alkane produces 2 mol of CO2 and 3 mol of H2O. Suggest the molecular formula of this alkane. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 20 Official (Closed) - Non Sensitive Alkenes Alkenes are a homologous series of hydrocarbons that contain one or more carbon- carbon double bonds.  they are unsaturated hydrocarbons. Alkenes have the general formula C H2n, n where n = number of carbon atoms) Name No. of C atoms Molecular formula Ethene 2 C 2H 4 Propene 3 C 3H 6 Butene 4 C 4H 8 Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 21  Official (Closed) - Non Sensitive Structural formulae of alkenes Name Molecular formula Structural formula Ball-and-stick model Ethene C 2H 4 H H C C H H Propene C 3H 6 H H H H C C C H H Butene C 4H 8 H H H H H C C C C H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 22  Official (Closed) - Non Sensitive Isomerism in alkenes H H H C C C H H H H H H H C C C C H H C H H H H Butene Methylpropene Straight-chain alkene Branched-chain alkene Melting point -185 ᵒC Melting point -140 ᵒC Boiling point -6.5 ᵒC Boiling point -6.9 ᵒC Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 23 Official (Closed) - Non Sensitive Try it yourself For propene, provide the: a) Molecular formula b) Structural formula c) Dot-and-cross diagram Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 24 Official (Closed) - Non Sensitive Physical properties of alkenes Ethene, propene & butene are gases at room temperature. The boiling point of an alkene increases as the number of carbon atoms in the molecule increases. Name Boiling point/°C Physical state at r.t.p. Ethene -104 Gas Propene -48 Gas Butene -6 Gas Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 25  Official (Closed) - Non Sensitive Chemical properties of alkenes Alkenes undergo combustion and addition reactions. Combustion Alkenes burn in excess oxygen to form carbon dioxide & water vapour Alkene + oxygen  carbon dioxide + water vapour E.g.: Ethene + oxygen  carbon dioxide + water vapour C2H4 (g) + 3O2 (g)  2CO2 (g) + 2H2O (g) Since alkenes have a relatively higher percentage of carbon than the corresponding alkanes, carbon particles may be produced on combustion. Hence, alkenes burn with a sootier flame than alkanes with a similar number of carbon atoms. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 26 Official (Closed) - Non Sensitive Addition reactions Addition of hydrogen (hydrogenation) At 200 ᵒC and in the presence of a catalyst such as nickel, alkenes can react with hydrogen to form alkanes. E.g.: H H H H o 200 C , N i C C + H H H C C H H H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 27 Official (Closed) - Non Sensitive Addition reactions Addition of bromine (bromination) If an alkene is added to a solution of bromine, the reddish-brown colour disappears immediately and a colourless liquid is formed. E.g.: Ethene + bromine  1,2-dibromoethane C2H4 (g) + Br2 (aq)  C2H4Br2 (l) H H H H C C + Br Br H C C H H H Br Br Used as a chemical test for the presence of unsaturated hydrocarbons. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 28 Official (Closed) - Non Sensitive Addition reactions Addition of steam (hydration) Alkenes can react with steam to produce alcohols. phosphoric (V) acid E.g.: phosphoric (V) acid phosphoric (V) acid H H o H H 300 C , 60 atm C C + H O H H 3P O 4 H C C H H H H O H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 29 Official (Closed) - Non Sensitive Addition reactions Addition polymerisation At high temperature and pressure, and in the presence of a catalyst, ethene molecules can react with each other to form a long molecule called polyethene. catalyst H H H H h ig h te m p e ra tu re a n d p re ssu re n C C C C ca ta lyst H H H H n Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 30 Official (Closed) - Non Sensitive Try it yourself Compound Y reacts with steam to form compound Z. The structural formula of Z is given. Draw the structural formula of Y. H H H H C C C H H H OH Z Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 31 Official (Closed) - Non Sensitive Alkanes & alkenes - similarities Both alkanes & alkenes are hydrocarbons Both alkenes & alkanes are flammable. On complete combustion, they form carbon dioxide and water. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 32  Official (Closed) - Non Sensitive Alkanes & alkenes - differences Property Alkanes Alkenes Molecular Contains only single bonds Contains double bonds structure between carbon atoms between carbon atoms Reactivity Generally unreactive Very reactive Type of reaction Undergoes substitution Undergoes addition reactions reactions Reaction with Does not react with Rapidly decolourises aqueous bromine aqueous bromine under aqueous bromine normal conditions Flammability Produces a less smoky flame Produces a smokier flame than an alkene with a similar than an alkane with a similar number of C atoms number of C atoms Ability to undergo Does not undergo Undergoes addition polymerisation polymerisation polymerisation 33 Official (Closed) - Non Sensitive Alcohols Alcohols are a homologous series of organic compounds which have the hydroxyl (-OH) functional group. Alcohols have the general formula C H2n+1OH, n where n = number of carbon atoms. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 34 Official (Closed) - Non Sensitive Production of ethanol Ethanol can be produced from 1. The catalytic addition of steam to ethene H H o H H 300 C , 60 atm C C + H O H H 3P O 4 H C C H H H H O H 2. The fermentation of glucose In the absence of oxygen, microorganisms (e.g. yeast) convert glucose to ethanol & carbon dioxide. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 35 Official (Closed) - Non Sensitive Uses of ethanol In alcoholic drinks As a solvent As a fuel Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 36  Official (Closed) - Non Sensitive Structural formulae of alcohols Name Molecular formula Structural formula Methanol CH3OH H H C O H H Ethanol C2H5OH H H H C C O H H H Propanol C3H7OH H H H H C C C O H H H H Butanol C4H9OH H H H H H C C C C O H H H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 37 Official (Closed) - Non Sensitive Physical properties of alcohols As the number of carbon atoms in the molecule increases, Solubility decreases Boiling point increases. The forces of attraction between the molecules increase. Name Physical state Solubility in water Boiling point/ ᵒC Methanol Liquid Very soluble 65 Ethanol Liquid Very soluble 78 Propanol Liquid Soluble 97 Butanol Liquid Slightly soluble 118 Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 38 Official (Closed) - Non Sensitive Chemical properties of alcohols Alcohols undergo combustion and oxidation reactions. Combustion Alcohols burn in excess oxygen to form carbon dioxide & water vapour Alcohol + oxygen  carbon dioxide + water vapour E.g.: Ethanol + oxygen  carbon dioxide + water vapour C2H5OH (l) + 3O2 (g)  2CO2 (g) + 3H2O (g) Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 39 Official (Closed) - Non Sensitive Chemical properties of alcohols Oxidation Alcohols undergo oxidation when heated with an oxidizing agent. Complete oxidation of a primary alcohol yields carboxylic acid and water. E.g.: oxygen from heat ethanol + ethanoic acid + water oxidising agent H H H O heat H C C O H + 2 [O ] H C C O H + H2O H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 40 Official (Closed) - Non Sensitive Question An alcohol has the molecular formula C4H10O. a) Draw the structural formula of this alcohol. b) Give 1 physical property & 1 chemical property of this alcohol. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 41 Official (Closed) - Non Sensitive Carboxylic acids Carboxylic acids are a homologous series of organic acids which have the carboxyl (-COOH) functional group. The general formula of carboxylic acids is CnH2n+1COOH, where n = number of carbon atoms. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 42  Official (Closed) - Non Sensitive Production of ethanoic acid Ethanoic acid is a colourless liquid. It is found in vinegar. Ethanoic acid is formed from the oxidation of ethanol: By oxidizing agents such as potassium manganate (VII) By atmospheric oxygen (in the presence of certain bacteria) Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 43  Official (Closed) - Non Sensitive Structural formulae of carboxylic acids Name Molecular formula Structural formula Methanoic HCOOH O acid H C O H Ethanoic acid CH3COOH H O H C C O H H Propanoic C2H5COOH H H O acid H C C C O H H H Butanoic C3H7COOH H H H O acid H C C C H C O H H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 44 Official (Closed) - Non Sensitive Physical properties of carboxylic acids As the number of carbon atoms in the molecule increases, Solubility decreases Boiling point increases. The forces of attraction between the molecules increase. Name Boiling point/ ᵒC Methanoic acid 101 Ethanoic acid 118 Propanoic acid 141 Butanoic acid 164 These carboxylic acids are all soluble in water. Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 45 Official (Closed) - Non Sensitive Chemical properties of carboxylic acids Carboxylic acids are weak acids – ionise only partially in aqueous solution. E.g. ethanoic acid CH3COOH (aq) ⇌ CH3COO-(aq) + H+(aq) H O H O - H C C O H H C C O + H + H H Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 46  Official (Closed) - Non Sensitive Acidic properties of carboxylic acids Being acidic, carboxylic acids react with reactive metals, carbonates and bases. E.g. 2CH3COOH(aq) + Mg(s)  (CH3COO)2Mg(aq) + H2(g) 2CH3COOH(aq) + Na2CO3(aq)  2CH3COONa(aq) + CO2(g) + H2O(l) CH3COOH(aq) + NaOH(aq)  CH3COONa(aq) + H2O(l) The salts of ethanoic acid are known as ethanoates. E.g. sodium ethanoate, magnesium ethanoate Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 47  Official (Closed) - Non Sensitive Reaction with alcohols (esterification) Carboxylic acids react with alcohols to give an ester and water. Concentrated sulfuric acid is used as a catalyst. E.g. conc. sulfuric acid Ethanoic acid + ethanol ethyl ethanoate + water conc. H2SO4 CH3COOH(aq) + C2H5OH(aq) CH3COOC2H5 (aq) + H2O(l) H O H H H O H H H C C O H + H O C C H H C C O C C H + H O H H H H H H H ester linkage Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 48  Official (Closed) - Non Sensitive Naming esters The name of an ester consists of 2 parts. E.g.: H O H The first part is The second part is derived from the H C O C C H derived from the alcohol, methanol. carboxylic acid, ethanoic acid. H H methyl ethanoate Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 49 Official (Closed) - Non Sensitive Questions Identify the substances in the reactions below: a) Sodium hydroxide + _______________________  sodium methanoate + water b) Methanol + _________________________  methyl ethanoate + water c) Propanoic acid + Mg  ______________ (gas) + ______________________________ Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 50  Official (Closed) - Non Sensitive Questions Write the formulae of the organic compounds that are required to prepare the following esters: a) CH3COOCH2CH2CH3 (smells like pears) b) CH3COOCH2CH2CH2CH2CH3 (smells like bananas) Principles of Chemistry, PFP, LSCT, Ngee Ann Polytechnic 51