Organic Chemistry Lesson 10 Reactions of Organic Molecules Combusition Reactions Substitution Reactions

Physical Sciences Grade 12 1 Instructions Lesson 10 (16 April 2020) 1. Read ALL the slides in this document. 2. Homework: Just understand the theory for now. 

• If you have any questions, post them onto your WhatsApp group and your teacher will attend to them when (s)he has a chance. • Additional Resources: • Summary on pg.132 of your textbook.

Physical Sciences Grade 12 2 Types of Reactions of Organic Compounds

1. Esterification: formation of an ester from an alcohol and a carboxylic acid. 2. Combustion Reactions (aka Oxidation): organic molecule + oxygen. 3. Substitution Reactions: one or more atoms are replaced by other atoms. (i) alkanes to alkyl halides; (ii) alcohols to alkyl halides; (iii) alkyl halides to alcohols 4. Addition Reactions: one or more atoms are added. (i) hydrogenation; (ii) halogenation; (iii) hydrohalogenation; (iv) hydration 5. Elimination Reactions: one or more atoms are removed. (i) dehydrohalogenation; (ii) dehydration; (iii) cracking of alkanes

Physical Sciences Grade 12 3 1. Esterification

• Already discussed (refer to earlier notes).

Physical Sciences Grade 12 4 2. Combustion Reactions, i.e. Oxidation • A combustion reaction is the reaction of an organic molecule with oxygen. • Please note: “combustion” does NOT mean “explosion”. All combustion reactions release energy but most do so WITHOUT any explosion. • Alkanes – in the form of fossil fuels – are currently the main source of energy worldwide as their combustion is highly exothermic. • Examples:  Burning wood for a braai.  Propane combusting in a gas stove.  Petrol combusting in a car engine.

Physical Sciences Grade 12 5 2. Combustion Reactions, i.e. Oxidation • Combustion of Alkanes:

alkane + 푂2 푔 → 퐶푂2 푔 + 퐻2푂 푔 ∆퐻 < 0

• Steps for Balancing: 1. Balance the carbon and hydrogen atoms first. 2. Balance the oxygen atoms second by dividing the total number of oxygen atoms on the RHS by 2. 3. If step 2 leads to a fraction, multiply every coefficient by 2.

Physical Sciences Grade 12 6 Examples (Combustion Reactions)

Physical Sciences Grade 12 7 Examples (Combustion Reactions)

Physical Sciences Grade 12 8 Examples (Combustion Reactions)

Here are two examples for you to attempt: e.g.3 Propane is used as a fuel in some gas stoves. Write out a balanced combustion reaction for propane. e.g.4 Butane is also sometimes used as a fuel in gas stoves. Write out a balanced combustion reaction for butane.

Fist pump for the first person to post a correct solution on the WhatsApp group.

Physical Sciences Grade 12 9 3. Substitution Reactions

• A substitution reaction involves one or more atoms being replaced by another atom or group of atoms in an organic molecule. • Substitution reactions take place in saturated organic compounds like alkanes, alkyl halides and alcohols. • Grade 12 Substitution Reactions: 1. Halogenation of alkanes to produce alkyl halides. 2. Reactions of 퐻푋 (푋 = 퐶푙, 퐵푟) with alcohols to produce alkyl halides. 3. Hydrolysis of alkyl halides to produce alcohols.

Physical Sciences Grade 12 10 Substitution Reactions: Alkanes to Alkyl Halides

• Alkanes will react with free radicals, i.e. atoms with an unpaired electron. • In the presence of light (ℎ푓) and heat (∆), a halogen atom (푋) will replace a hydrogen atom on an alkane to form an alkyl halide. • This reaction is difficult to stop and additional substitution reactions will occur.

ℎ푓 • Reaction: alkane + 푋2 → alkyl halide + 퐻푋 푋 = 퐹, 퐶푙, 퐵푟 or 퐼 ∆

Physical Sciences Grade 12 11 Substitution Reactions: Alkanes to Alkyl Halides

Physical Sciences Grade 12 12 Substitution Reactions: Alkanes to Alkyl Halides

Physical Sciences Grade 12 13 Organic Chemistry Lesson 11 Substitution Reactions

Physical Sciences Grade 12 14 Instructions Lesson 11 (17 April 2020) 1. Read ALL the slides in this document. 2. Homework: Think Tank 10.3, pg.134 Q 8 ; 9 ; 10

• If you have any questions, post them onto your WhatsApp group and your teacher will attend to them when (s)he has a chance. • Additional Resources: • Summary on pg.132 of your textbook. • Substitution & Esterification Reactions: www.youtube.com/watch?v=EcrMHmo-YsY

Physical Sciences Grade 12 15 Types of Reactions of Organic Compounds

Physical Sciences Grade 12 16 3. Substitution Reactions

Physical Sciences Grade 12 17 Substitution Reactions: Alcohols ⇌ Alkyl Halides

• Since the hydroxyl group (−푂퐻) in alcohols and the halogen in alkyl halides usually occupy similar positions in the molecule, the two groups can be substituted with each other. • In other words, an interconversion reaction can occur where an alcohol can be reacted to form an alkyl halide and vice versa.

• Reaction: alcohol + 퐻푋 → alkyl halide 푋 = 퐹, 퐶푙, 퐵푟 or 퐼 ∆ • Heat is needed for primary and secondary alcohols to react with 퐻푋. • Tertiary alcohols DO NOT require heat and will react at room temperature.

Physical Sciences Grade 12 18 Substitution Reactions: Alcohols ⇌ Alkyl Halides

Physical Sciences Grade 12 19 Examples (Alcohols ⇌ Alkyl Halides)

Here are two examples for you to attempt: Use structural and condensed structural formula to show the reaction between: e.g.1 ethanol and hydrochloric acid e.g.2 3-methylbutan-2-ol and HBr

High five for the first person to post a correct solution on the WhatsApp group.

Physical Sciences Grade 12 20 Substitution Reactions: Alcohols ⇌ Alkyl Halides

ethanol • Reaction: alkyl halide + base → alcohol + 푵풂푋 ; 푋 = 퐹, 퐶푙, 퐵푟 or 퐼 ∆ • 푁푎푂퐻 or 퐾푂퐻 are appropriate bases to use. • The alkyl halide and base must be dissolved in ethanol (as alkyl halides do not mix with water). • The solution also needs to be warmed for the reaction to occur.

Physical Sciences Grade 12 21 Substitution Reactions: Alcohols ⇌ Alkyl Halides

Physical Sciences Grade 12 22 Examples (Alcohols ⇌ Alkyl Halides)

Here are two examples for you to attempt: Use structural and condensed structural formula to show the reaction between: e.g.1 2-chloro-2-methylpropane and NaOH e.g.2 1-fluoro-2,2-dimethylpropane and NaOH

Chocolate for the first person to post a correct solution on the WhatsApp group.

Physical Sciences Grade 12 23 Substitution Reactions: Hydrolysis

• Hydrolysis is the reaction of an alkyl halide with water to form an alcohol and a hydrogen halide. • The alkyl halide must be dissolved in ethanol.

• Reaction: alkyl halide + 퐻2푂 → alcohol + 퐻푋 푋 = 퐹, 퐶푙, 퐵푟 or 퐼

Physical Sciences Grade 12 24 Substitution Reactions: Hydrolysis

Physical Sciences Grade 12 25 Examples (Hydrolysis)

Here are two examples for you to attempt: Use structural and condensed structural formula to show the reaction between: e.g.1 the hydrolysis of 2-chloropropane e.g.2 the hydrolysis of 3-methyl-2-fluorobutane

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Physical Sciences Grade 12 26 Organic Chemistry Lesson 11 Homework Solutions

Physical Sciences Grade 12 27 Physical Sciences Grade 12 28 Physical Sciences Grade 12 29 Substitution Reactions: Alcohols ⇌ Alkyl Halides

Physical Sciences Grade 12 30 Organic Chemistry Lesson 12 Addition Reactions

Physical Sciences Grade 12 31 Instructions Lesson 12 (20 April 2020) 1. Read ALL the slides in this document. 2. Homework: Think Tank 10.3, pg.133-134 Q 1 ; 2 ; 3 ; 11

• If you have any questions, post them onto your WhatsApp group and your teacher will attend to them when (s)he has a chance. • Additional Resources: • Summary on pg.131 of your textbook. • Organic Reactions – Addition: www.youtube.com/watch?v=5AOg7B44wt0

Physical Sciences Grade 12 32 Primary, Secondary and Tertiary Carbons

• A primary carbon is a carbon atom bonded to one other carbon atom. • A secondary carbon is a carbon atom bonded to two other carbon atoms. • A tertiary carbon is a carbon atom bonded to three other carbon atoms. • A quaternary carbon is a carbon atom bonded to four other carbon atoms.

Physical Sciences Grade 12 33 Types of Reactions of Organic Compounds

Physical Sciences Grade 12 34 4. Addition Reactions

• An addition reaction involves one or more atoms being added to an organic molecule, usually over a double/triple bond. • The addition of atoms causes the double/triple bond to BREAK. • Addition reactions take place in unsaturated organic compounds like alkenes. • Grade 12 Addition Reactions:

1. Hydrogenation (addition of 퐻2 to an alkene).

2. Halogenation (addition of 푋2 to an alkene). 푋 = a halogen atom. 3. Hydrohalogenation (addition of 퐻푋 to an alkene). 4. Hydration (addition of water to an alkene). Physical Sciences Grade 12 35 Addition Reactions: Hydrogenation

• Hydrogenation is the addition of hydrogen (퐻2) to an alkene. • In order for hydrogenation to occur, the alkene must be dissolved in a non-polar solvent. • The presence of a catalyst (푃푡 or 푃푑 or 푁𝑖) is required to lower the activation energy of the reaction by providing an area where the reactants can come into closer contact with one another. 푃푡\푃푑\푁푖 • Reaction: alkene + 퐻2 alkane

Physical Sciences Grade 12 36 Addition Reactions: Hydrogenation

Physical Sciences Grade 12 37 Addition Reactions: Halogenation

• Halogenation is the addition of a halogen molecule (푋2) to an alkene. • Halogenation will occur easily at room temperature. • The bromine water test, which is used to test for the presence of alkenes (discussed previously), is an example of a halogenation reaction. (Watch: www.youtube.com/watch?v=vBMGNzRYngk).

• Reaction: alkene + 푋2 → alkyl halide 푋 = a halogen atom

Physical Sciences Grade 12 38 Addition Reactions: Halogenation

Physical Sciences Grade 12 39 Addition Reactions: Hydrohalogenation

• Hydrohalogenation is the addition of a hydrogen halide (퐻푋) to an alkene. • Hydrohalogenation will only take place if there is NO water present. • Reaction: alkene + 퐻푋 → alkyl halide 푋 = a halogen atom

Physical Sciences Grade 12 40 Addition Reactions: Hydrohalogenation

Physical Sciences Grade 12 41 Addition Reactions: Hydrohalogenation

• Markovnikov’s Rule: (i.e. “the rich get richer” rule)

When a polar molecule (e.g. 퐻퐵푟 or 퐻2푂) is added to an alkene, the hydrogen atom adds to the carbon atom in the alkene that has the greatest number of hydrogen atoms.

Physical Sciences Grade 12 42 Addition Reactions: Hydrohalogenation

Physical Sciences Grade 12 43 Addition Reactions: Hydration

• Hydration is the addition of water to an alkene. • Hydration requires a dilute, strong acid solution to act as a catalyst.

• 50% 퐻2푆푂4 푎푞 or 50% 퐻3푃푂4 푎푞 are appropriate acids to use as catalysts.

50% 퐻2푆푂4 • Reaction: alkene + 퐻2푂 alcohol • Markovnikov’s rule also applies to hydration reactions.

Physical Sciences Grade 12 44 Addition Reactions: Hydration

Physical Sciences Grade 12 45 Examples of Addition Reactions

Here are some examples for you to try. Use structural formula to write out the following reactions, then name the product(s) formed: e.g.1 The hydrogenation of 3-methyl-1-butene. e.g.2 The halogenation of 2-methyl-2-pentene. e.g.3 The hydrohalogenation of 3-methylhex-2-ene. e.g.4 The hydration of 2-methylhex-2-ene.

Happy dance for the first person to post a correct solution on the WhatsApp group.

Physical Sciences Grade 12 46 Organic Chemistry Lesson 12 Homework Solutions

Physical Sciences Grade 12 47 Physical Sciences Grade 12 48 Physical Sciences Grade 12 49 Organic Chemistry Lesson 13 Elimination Reactions

Physical Sciences Grade 12 50 Instructions Lesson 13 (21 April 2020) 1. Read ALL the slides in this document. 2. Homework: Think Tank 10.3, pg.133-135 Questions 4 ; 5 ; 6 ; 13

• If you have any questions, post them onto your WhatsApp group and your teacher will attend to them when (s)he has a chance. • Additional Resources: • Summary on pg.131-132 of your textbook. • Organic Reactions – Elimination: www.youtube.com/watch?v=Y9T-Qnc-Kaw • Fractional Distillation: www.youtube.com/watch?v=PYMWUz7TC3A • Crude Oil Fractions: www.youtube.com/watch?v=JZdvsQzOKuk • Hydrocarbon Cracking: www.youtube.com/watch?v=Xsqlv4rWnEg

Physical Sciences Grade 12 51 Types of Reactions of Organic Compounds

Physical Sciences Grade 12 52 5. Elimination Reactions

• An elimination reaction involves one or more atoms being removed from an organic molecule, usually leaving a double/triple bond in their place. • The elimination of atoms causes the double/triple bond to FORM. • Elimination reactions take place in saturated organic compounds like alkanes and alcohols. • Grade 12 Elimination Reactions: 1. Dehydrohalogenation (removal of 퐻 and a halogen from an alkyl halide). 2. Dehydration (removal of water from an alcohol). 3. Cracking of Alkanes (breaking up of large hydrocarbon molecules). Physical Sciences Grade 12 53 Elimination Reactions: Dehydrohalogenation

• Dehydrohalogenation is the elimination of a hydrogen atom and a halogen atom from an alkyl halide to form an alkene. • Dehydrohalogenation requires the presence of a concentrated solution of either 푁푎푂퐻 or 퐾푂퐻 with pure ethanol as the solvent. • The alkyl halide, in solution, has to be heated under reflux. • Reaction: alkyl halide → alkene + 퐻푋 푋 = a halogen atom

Physical Sciences Grade 12 54 Reflux

• Reflux is a common chemical technique involving the condensation of vapours. • The liquid reactants are heated to form a vapour which rises in the tube. • The vapour in the tube is cooled by water passing around the tube and condensing back into liquid form. The process then repeats itself. • Note: the water and the reactants NEVER come into physical contact with each other. Physical Sciences Grade 12 55 Elimination Reactions: Dehydrohalogenation

Physical Sciences Grade 12 56 Elimination Reactions: Dehydrohalogenation

• Zaitsev’s Rule: (i.e. the “poor gets poorer” rule) The major product in an elimination reaction is the one formed by removing the hydrogen bonded to the carbon with the smallest number of 퐻 atoms.

Physical Sciences Grade 12 57 Elimination Reactions: Dehydrohalogenation

Physical Sciences Grade 12 58 Substitution vs. Elimination Reactions

• Substitution and elimination (dehydrohalogenation) reactions will compete with each other. • The preferred product will depend on whether a PRIMARY, SECONDARY or TERTIARY halide is involved:

• Primary halides will undergo substitution. • Secondary and tertiary halides will undergo a mixture of substitution and elimination. Physical Sciences Grade 12 59 Elimination Reactions: Dehydrohalogenation

Here are some examples for you to try – see if you can be the first person to post the correct solution on your WhatsApp group.

Using structural and condensed structural formulae, write out the equation for: e.g.1 The dehydrohalogenation of 2-chloropentane. e.g.2 The dehydrohalogenation of 퐶퐻2퐵푟퐶퐻퐵푟퐶퐻3.

Name the organic products.

Physical Sciences Grade 12 60 Elimination Reactions: Dehydration

• Dehydration is the elimination of a water molecule from an alcohol. • Dehydration requires the heating on an alcohol in an excess of concentrated sulphuric (or phosphoric) acid solution.

conc. 퐻2푆푂4 • Reaction: alcohol alkene + 퐻2푂 • Zaitsev’s rule also applies to dehydration reactions.

Physical Sciences Grade 12 61 Elimination Reactions: Dehydration

Physical Sciences Grade 12 62 Elimination Reactions: Dehydrohalogenation

Here are some examples for you to try – see if you can be the first person to post the correct solution on your WhatsApp group.

Using structural and condensed structural formulae, write out the equation for: e.g.3 The dehydration of propanol. e.g.4 The dehydration of 2-pentanol.

Name the organic products.

Physical Sciences Grade 12 63 Elimination Reactions: Cracking of Alkanes

• Cracking is the chemical process given to the breaking up of large hydrocarbon molecules into smaller and more useful molecules. • 2 Types of Cracking: 1. Thermal Cracking – uses high pressures (up to 70 푎푡푚) and high temperatures (450°퐶 to 750°퐶) without the use of a catalyst. 2. Catalytic Cracking – uses a catalyst and a fractional distillation column.

Physical Sciences Grade 12 64 Elimination Reactions: Cracking of Alkanes

Physical Sciences Grade 12 65 Organic Chemistry Lesson 13 Homework Solutions

Physical Sciences Grade 12 66 Physical Sciences Grade 12 67 Physical Sciences Grade 12 68 Physical Sciences Grade 12 69 Organic Chemistry Lesson 14 Polymers

Physical Sciences Grade 12 70 Instructions Lesson 14 (22 April 2020) 1. Watching the following videos: i. Addition Polymerisation: www.youtube.com/watch?v=NXEjzF4AfYc ii. Condensation Polymerisation: www.youtube.com/watch?v=QBuSFPOtcJ4 2. Read ALL the slides in this document. 3. Homework: Think Tank 12.1, pg.150-151, Questions 5 ; 6 Think Tank 12.2, pg.154-155, Question 2 • If you have any questions, post them onto your WhatsApp group and your teacher will attend to them when (s)he has a chance. • Additional Resources: • Monomers & Polymers: www.youtube.com/watch?v=jRMNbZOkNH0 (00:00  01:30) • Polymerisation of Ethene: www.youtube.com/watch?v=sk6h4oaArE0 • Broad Overview (lots of extra info): www.youtube.com/watch?v=rHxxLYzJ8Sw&t=396s

Physical Sciences Grade 12 71 Terminology

• A macromolecule is a molecule that consists of a large number of atoms. • Monomers are small organic molecules that can be covalently bonded to each other in a repeating pattern. • A polymer is a large molecule composed of smaller monomer units covalently bonded to each other in a repeating pattern. • Polymerisation is a chemical reaction in which monomer molecules join to form a polymer. Physical Sciences Grade 12 72 Polymers & Polymerisation

• Polymers occur in nature, e.g. the rubber in a rubber tree, wool, silk and the cellulose in wood. • Synthetic polymers (i.e. plastics) are man-made, e.g. polyethylene, nylon and polylactic acid (PLA). • The type of polymerisation depends on the functional group of the monomers that are reacting. • 2 Types of Polymerisation: 1. Addition Polymerisation – the monomers are alkenes. 2. Condensation Polymerisation – the monomers are alcohols/carboxylic acids. Physical Sciences Grade 12 73 Addition Polymerisation

• An addition polymer is a polymer formed when monomers (usually containing a double bond) combine through an addition reaction. • Addition polymerisation is a reaction in which small molecules (alkenes) join to form very large molecules by adding on at double bonds. • In addition polymerization, thousands of unsaturated molecules join together to form a single molecule.

Physical Sciences Grade 12 74 Formation of Polyethene (Polyethylene)

• Polyethene, more commonly known as polyethylene, is a cheap plastic. • Polyethylene is used to make plastic bags, cling wrap and bulletproof vests. • Polyethene is a polymer formed by the addition reaction of ethene monomers. • The reaction requires high temperatures and The reaction very high pressures. shows a single unit of the • Reaction: polymer with the “푛” indicating that the unit is repeated a number of times.

Physical Sciences Grade 12 75 Condensation Polymerisation

• A condensation polymer is a polymer formed by monomers with two functional groups that are linked together in a condensation reaction in which a small molecule, usually water, is lost. • Condensation polymerisation is a reaction in which molecules of two monomers with different functional groups undergo condensation reactions with the loss of small molecules, usually water. • Condensation polymerisation is SLOWER than addition polymerisation.

Physical Sciences Grade 12 76 Formation of a Polyester

• Polyesters are formed the same way simple esters are with the exception that it involves a diol and a dicarboxylic acid.

• Reaction: The reaction shows a single unit of the polymer with the “푛” indicating that the unit is repeated a number of times.

Physical Sciences Grade 12 77 Addition vs. Condensation Polymerisation

• Condensation polymers are formed more slowly than addition polymers. • Water is formed in condensation polymerisation (similar to esterification). No by-products are formed during addition polymerisation. • Monomers of addition polymers contain carbon-carbon double bonds, i.e. unsaturated molecules. • Monomers of condensation polymers contain functional groups (such as the hydroxyl and carboxyl groups).

Physical Sciences Grade 12 78 Identifying Monomers from a Polymer

1. Find the repeating unit and place a bracket around it (work with the centre of the molecule).

2. Separate the repeating unit and insert a double bond between the carbons.

3. Name the monomer. chloroethene Physical Sciences Grade 12 79 Identifying Monomers from a Polymer e.g. Given the formula for polystyrene, determine the monomer.

Physical Sciences Grade 12 80 Organic Chemistry Lesson 14 Homework Solutions

Physical Sciences Grade 12 81 Physical Sciences Grade 12 82