Main Menu Lesson 9: Meet the Families….again Objectives: Learn to recognise and name a further 4 functional groups Use molecular models to build the above
Main Menu Functional Groups Mind map You need to add these functional groups to your mind map from lesson 3: Amide Amine Nitrile Ester – with the full detail now For each one you should include: General structural formula Rules for naming them (including the position where relevant) With an example Relative volatility and solubility in water For amines you should include a branch to explain the difference between 1 o, 2 o and 3 o You should spend time looking in more detail at the naming of the amines and amides as the N atom can complicate things
Main Menu Building Organic Compounds Use molecular models to make any of the compounds mentioned in your mind-map: Draw it (structural and skeletal) Name it Give it to a friend and challenge them to do the same Only go up to 6 carbons Only include branched-chains for the alkanes
Main Menu Key Points There are 11 functional groups we need to know in detail and 1 extra we need to be able to recognise We will look at each in detail at the 4 new ones over the rest of the unit
Main Menu Refresh What is the IUPAC name of the compound CH 3 CH 2 COOCH 2 CH 3 ? A. Ethyl ethanoate B. Propyl ethanoate C. Ethyl propanoate D. Pentyl propanoate Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect.
Main Menu Lesson 10: S N 1 and S N 2 Revisited Objectives: Understand why the nature of the halogenoalkane effects the mechanism of nucleophilic substitution reactions Understand why OH - is a better nucleophile than H 2 O Understand the effect of the halogen on the rate of nuclephilic substitution reactions Complete a short investigation into the factors affecting the rate of nucleophilic substitution
Main Menu S N 1 and the carbocation The carbocation is an unstable species, and will often immediately attract the halide ion straight back Alkyl groups surrounding the carbocation donate electron charge to it and stabilise it In this diagram, the arrows on the bonds represent the charge donated by the surrounding alkyl groups 3 o carbocations have most surrounding alkyl groups and therefore are most stable, thus S N 1 is preferred for 3 o halogenoalkanes
Main Menu Mechanism and rate For S N 1:rate = k[halogenoalkane] For S N 2:rate = k[halogenoalkane][nucleophile] Since S N 1 only depends on one reactant, it tends to be faster (all else being equal) than S N 2 Therefore, if we consider the rates of hydrolysis / substitution, as a rule of thumb: Tertiary > Secondary > Primary
Main Menu S N 2 and steric hindrance Alkyl groups are physically bulky, and make it difficult for a nucleophile to attack the carbon: this is called steric hindrance 1 o halogenoalkanes only have one surrounding alkyl group so steric hindrance is low and SN2 is favourable 3 o halogenoalkanes have three surrounding alkyl groups so steric hindrance is high and SN2 is unfavourable The black arrows on the diagram are supposed to show possible avenues of approach by the nucleophile, red crosses show where they are blocked
Main Menu Changing the Nucleophile Water can act as our nucleophile: Halogenoalkane + water alcohol + hydrogen halide However, hydroxide is much better. Why? Explain why using ideas from the bonding unit
Main Menu Changing the Halogen The rate of substitution / hydrolysis varies greatly depending on the halogen atom As a rule, with all else being equal, the rate changes as follows: Iodine > Bromine > Chlorine Explain why using ideas from the bonding unit
Main Menu Key Points The substitution mechanism followed depends on: Stabilisation of the carbocation by surrounding alkyl groups Steric hindrance of the carbocation by surrounding alkyl groups Hydroxide ions are better nucleophiles than water due to their strong negative charge Iodoalkanes react faster than chloroalkanes due to the C-I bond being weaker than the C-Cl bond
Main Menu Refresh Which statements about substitution reactions are correct? I. The reaction between sodium hydroxide and 1-chloropentane predominantly follows an S N 2 mechanism. II. The reaction between sodium hydroxide and 2-chloro-2-methylbutane predominantly follows an S N 2 mechanism. III. The reaction of sodium hydroxide with 1- chloropentane occurs at a slower rate than with 1-bromopentane. A. I and II only B. I and III only C. II and III only D. I, II and III Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect.
Main Menu Lesson 11: More Nucleophiles Objectives: Understand the reaction of halogenoalkanes with ammonia Understand the reaction of halogenoalkanes with potassium cyanide Describe and explain the reduction of nitriles
Main Menu More nucleophiles So far we have met two nucleophiles: Hydroxide Water This lesson we meet two more: Ammonia, NH3 Cyanide, - CN Draw the Lewis structure of cyanide These undergo participate in nucleophilic substitution in exactly the same way as hydroxide and water.
Main Menu Key Points Halogenoalkanes react with: Ammonia to form primary amines Further reactions can for secondary and tertiary amines and quaternary ammonium salts Potassium cyanide to form a nitrile This is useful as it creates a new C-C bond…no mean feat! The nitrile can be reduced to an amine by reaction with H 2 and Ni catalyst
Main Menu Refresh What is the product of the following reaction? CH 3 CH 2 CH 2 CN + H 2 A. CH 3 CH 2 CH 2 NH 2 B. CH 3 CH 2 CH 2 CH 3 C. CH 3 CH 2 CH 2 CH 2 CH 3 D. CH 3 CH 2 CH 2 CH 2 NH 2 Ni. cat Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect.
Main Menu Lesson 12: Elimination Reactions Objectives: Describe with equations the elimination reactions of halogenoalkanes Describe the mechanism of elimination reactions Complete an experiment investigating elimination reactions
Main Menu Elimination With warm, aqueous sodium hydroxide, halogenoalkanes undergo substitution With hot, ethanolic sodium hydroxide an elimination reaction will take place: halogenoalkane + sodium hydroxide alkene + water + sodium halide
Main Menu The mechanism Similar to substitution, there are unimolecular (E1) and bimolecular (E2) mechanisms: They work in a similar way to S N 1/2 and are affected by similar factors: E1: E2: You only need remember one (go with E2…shorter), and do not need to know the same level of detail as for substitution
Main Menu Key Points Halogenoalkanes will undergo elimination on reaction with sodium hydroxide if: It is dissolved in ethanol Hot The elimination proceeds by both bimolecular and unimolecular mechanisms
Main Menu Lesson 13: Condensation Reactions Objectives: Describe with equations the reaction of alcohols with carboxylic acids Describe with equations the reaction of amines with carboxylic acids Complete a lovely-smelling esters experiment
Main Menu Condensation Reactions A reaction in which two molecules join together, and produce a molecule of water as a by-product.
Main Menu Esterification – the reaction of alcohols and carboxylic acids Carboxylic acids react with alcohols to make esters: The ester linkage is outline in red Carboxylic acid + alcohol ester + water You may need to review your mind-map for details on naming esters…basically the alcohol gives the ‘-yl’ part and the acid the ‘- oate’ part H + cat
Main Menu Amides – the reaction of amines and carboxylic acids Carboxylic acids react with amines to make amides: The amide linkage is outlined in red Carboxylic acid + amine amide + water You may need to review your mind-map for details on naming esters The amine gives the ‘-yl’ part and the acid the ‘-anamide’ part, the N- signifies that the alkyl group is attached to the nitrogen Note the similarity to esterification
Main Menu Draw and name the products of the following reactions: Ethanoic acid with ethanol Methanoic acid with butylamine Pentanoic acid with phenol (C 6 H 5 OH) Propanoic acid with methylamine
Main Menu Key Points Carboxylic acid + alcohol ester + water Carboxylic acid + amine amide + water
Main Menu Lesson 14 Condensation Polymerisation
Main Menu Refresh What is the IUPAC name of CH 3 CH 2 CONH 2 ? A. Aminopropanal B. Ethanamide C. Propylamine D. Propanamide Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect.
Main Menu Lesson 14: Condensation Reactions Objectives: Describe with equations the condensation reactions of diacids with diols Describe with equations the condensation reactions of diacids with diamides Perform the nylon rope-trick
Main Menu Polyesters Polyesters form from monomers containing two functional groups For example dicarboxylic acids and dialcohols Each end of each molecule forms an ester linkage, allowing for long chains to build up
Main Menu Polyamides Similar to polyesters, polyamides form from monomers containing two functional groups For example dicarboxylic acids and diamines Each end of each molecule forms an amide linkage, allowing for long chains to build up
Main Menu A quick note You can also get condensation polymerisation from monomers containing one of each of the functional groups. The best example is amino acids and proteins:
Main Menu Key Points Polyesters form from monomers containing two acid and two alcohol groups Polyamides form from monomers containing two acid and two amine groups
Main Menu Refresh Which formula represents a polyamide? A. ( CH 2 –CHCl ) n B. ( NH–(CH 2 ) 6 –NH–CO–(CH 3 ) 4 – CO ) n C. ( CF 2 –CF 2 ) n D. ( O–(CH 2 ) 2 –O–CO–--–CO ) n Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect.
Main Menu Lesson 15: Geometrical Isomerism Objectives: Understand the term stereoisomerism Understand and identify geometrical isomerism Understand the chemical significance of cis-trans isomerism
Main Menu Stereoisomerism Stereoisomers are compounds with the same structural formula but different 3D arrangement of atoms There are two types of stereoisomerism: Geometrical isomerism Optical isomerism
Main Menu Geometrical (cis-trans isomerism) It happens because double bonds are not free to rotate Each C=C carbon must have two different groups attached to it. In the trans isomer, the substituents (the –CH3 groups) are on opposite sides of the double bond In the cis isomer, the substituents are on the same side of the double bond Geometric isomerism involves the arrangement of groups around a double bond Or a single bond that can’t rotate freely such as in a cyclic compound
Main Menu Properties Chemical and physical properties will often be similar but there can be important differences as you are about to see….
Main Menu Chemical properties of geometric isomers Can be different For example: Why do you think this happens? Hint: think about the previous couple of lessons
Main Menu Key Points Cis isomers: the substituents are on the same side Trans isomers: the substituents are on opposite sides Cis alkenes have lower mp/bp than trans due to ‘rounder’ shape Cis halogenoalkenes have higher mp/bp due to polarity Chemical properties can be different where cis brings groups close enough to react
Main Menu Lesson 16: Optical Isomerism Objectives: Understand and identify optical isomerism Understand the chemical significance of optical isomerism
Main Menu Optical Isomerism Optical isomerism occurs when you have four different groups all bonded to a central atom. For example: amino acids
Main Menu Some terminology The central carbon is referred to as ‘chiral’ You will see books refer to the ‘chiral carbon’ or ‘chiral centre’ You may see books talking about the ‘chirality’ of a molecule A molecule might be described as ‘chiral’ if it has a ‘chiral centre’ A carbon must have at least 4 different groups to be chiral The two optical isomers are referred to as enantiomers A racemic mixture is a one with a 50:50 mix of the two enantiomers Enantiomers can be referred to as right or left handed If you see ‘R-’ or ‘L-’ in a name, this is what they are referring to There is a standard way to work this out but we don’t need it!
Main Menu Properties of optical isomers Enantiomers share virtually identical chemical and physical properties However: Two enantiomers will rotate plane- polarised light in opposite directions…hence the term ‘optical isomerism’ More on the next slide Chemical properties differ significantly in chemical systems where 3D-shape is important, particularly biochemistry The image above right shows an enzyme, these are sensitive to the exact shape of a molecule
Main Menu Rotation of plane-polarised light Light normally vibrates in many different directions Plane-polarised light only vibrates in one direction A pure solutions of enantiomers rotate the plane- polarised light in opposite directions A racemic mixture will not rotate light as the rotations from each enantiomer cancel each other out This rotation can be detected using a polarimeter
Main Menu Key Points Optical isomers (enantiomers) rotate plane-polarised light in opposite directions To display optical activity, a compound must have at least four different groups attached to the same atom The central atom is referred to as chiral
Main Menu Lesson 17 Reaction Pathways – Boss Level
Main Menu Lesson 17: Reaction Pathways Again Objectives: Add the HL reactions to the reaction pathways diagram Set your classmates challenges involving navigation around the diagram
Main Menu Some Challenges Use your reaction pathways diagrams to help you solve the following problems Butylamine can be produced from propane in three steps. Give the reaction conditions and draw the intermediate products for each step Ethyl ethanoate can be prepared from ethene over several steps. Outline how you might do this, naming the intermediate products and giving suitable reaction conditions
Main Menu Key Points Inter-converting between organic compounds is the bread and butter of an organic chemist Reaction pathways are the map that help you navigate from your point of origin to your destination