IB Syllabus ContentHL CHEMISTRY COURSE SYLLABUSTopic 12: Atomic structure (2 hours)
12.1 Electrons in atoms
Understandings:
• In an emission spectrum, the limit of convergence at higher frequency corresponds to the first ionization energy. • Trends in first ionization energy across periods account for the existence of main energy levels and sub-levels in atoms. • Successive ionization energy data for an element give information that shows relations to electron configurations. Applications and skills: • Solving problems using E = hv. • Calculation of the value of the first ionization energy from spectral data which gives the wavelength or frequency of the convergence limit. • Deduction of the group of an element from its successive ionization energy data. • Explanation of the trends and discontinuities in first ionization energy across a period. Guidance: • The value of Planck’s constant (h) and 𝐸𝐸 = ℎ𝑣𝑣 are given in the data booklet in sections 1 and 2. • Use of the Rydberg formula is not expected in calculations of ionization energy. International-mindedness: • In 2012 two separate international teams working at the Large Hadron Collider at CERN independently announced that they had discovered a particle with behaviour consistent with the previously predicted “Higgs boson”. Theory of knowledge: • “What we observe is not nature itself, but nature exposed to our method of questioning.”—Werner Heisenberg. An electron can behave as a wave or a particle depending on the experimental conditions. Can sense perception give us objective knowledge about the world? • The de Broglie equation shows that macroscopic particles have too short a wavelength for their wave properties to be observed. Is it meaningful to talk of properties which can never be observed from sense perception? Utilization: • Electron microscopy has led to many advances in biology, such as the ultrastructure of cells and viruses. The scanning tunnelling microscope (STM) uses a stylus of a single atom to scan a surface and provide a 3-D image at the atomic level. |
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Topic 13: The periodic table—the transition metals (4 hours)
13.1 First-row d-block elements
Understandings:
• Transition elements have variable oxidation states, form complex ions with ligands, have coloured compounds, and display catalytic and magnetic properties. • Zn is not considered to be a transition element as it does not form ions with incomplete d-orbitals. • Transition elements show an oxidation state of +2 when the s-electrons are removed. Applications and skills: • Explanation of the ability of transition metals to form variable oxidation states from successive ionization energies. • Explanation of the nature of the coordinate bond within a complex ion. • Deduction of the total charge given the formula of the ion and ligands present. • Explanation of the magnetic properties in transition metals in terms of unpaired electrons. Guidance: • Common oxidation numbers of the transition metal ions are listed in the data booklet in sections 9 and 14. International-mindedness: • The properties and uses of the transition metals make them important international commodities. Mining for precious metals is a major factor in the economies of some countries. Theory of knowledge: • The medical symbols for female and male originate from the alchemical symbols for copper and iron. What role has the pseudoscience of alchemy played in the development of modern science? 13.2 Coloured complexes
Understandings:
• The d sub-level splits into two sets of orbitals of different energy in a complex ion. • Complexes of d-block elements are coloured, as light is absorbed when an electron is excited between the d-orbitals. • The colour absorbed is complementary to the colour observed. Applications and skills: • Explanation of the effect of the identity of the metal ion, the oxidation number of the metal and the identity of the ligand on the colour of transition metal ion complexes. • Explanation of the effect of different ligands on the splitting of the d-orbitals in transition metal complexes and colour observed using the spectrochemical series. Guidance: • The spectrochemical series is given in the data booklet in section 15. A list of polydentate ligands is given in the data booklet in section 16. • Students are not expected to recall the colour of specific complex ions. • The relation between the colour observed and absorbed is illustrated by the colour wheel in the data booklet in section 17. • Students are not expected to know the different splitting patterns and their relation to the coordination number. Only the splitting of the 3-d orbitals in an octahedral crystal field is required. Topic 14: Chemical bonding and structure (7 hours)
14.1 Covalent bonding and electron domain and molecular geometries
Understandings:
• Covalent bonds result from the overlap of atomic orbitals. A sigma bond (σ) is formed by the direct head-on/end-to-end overlap of atomic orbitals, resulting in electron density concentrated between the nuclei of the bonding atoms. A pi bond (π) is formed by the sideways overlap of atomic orbitals, resulting in electron density above and below the plane of the nuclei of the bonding atoms. • Formal charge (FC) can be used to decide which Lewis (electron dot) structure is preferred from several. The FC is the charge an atom would have if all atoms in the molecule had the same electronegativity. FC = (Number of valence electrons)-½(Number of bonding electrons)-(Number of non-bonding electrons). The Lewis (electron dot) structure with the atoms having FC values closest to zero is preferred. • Exceptions to the octet rule include some species having incomplete octets and expanded octets. • Delocalization involves electrons that are shared by/between all atoms in a molecule or ion as opposed to being localized between a pair of atoms. • Resonance involves using two or more Lewis (electron dot) structures to represent a particular molecule or ion. A resonance structure is one of two or more alternative Lewis (electron dot) structures for a molecule or ion that cannot be described fully with one Lewis (electron dot) structure alone. Applications and skills: • Prediction whether sigma (σ) or pi (π) bonds are formed from the linear combination of atomic orbitals. • Deduction of the Lewis (electron dot) structures of molecules and ions showing all valence electrons for up to six electron pairs on each atom. • Application of FC to ascertain which Lewis (electron dot) structure is preferred from different Lewis (electron dot) structures. • Deduction using VSEPR theory of the electron domain geometry and molecular geometry with five and six electron domains and associated bond angles. • Explanation of the wavelength of light required to dissociate oxygen and ozone. • Description of the mechanism of the catalysis of ozone depletion when catalysed by CFCs and NOx. Guidance: • The linear combination of atomic orbitals to form molecular orbitals should be covered in the context of the formation of sigma (σ) and pi (π) bonds. • Molecular polarities of geometries corresponding to five and six electron domains should also be covered. International-mindedness: • How has ozone depletion changed over time? What have we done as a global community to reduce ozone depletion? • To what extent is ozone depletion an example of both a success and a failure for solving an international environmental concern? Theory of knowledge: • Covalent bonding can be described using valence bond or molecular orbital theory. To what extent is having alternative ways of describing the same phenomena a strength or a weakness? Utilization: • Drug action and links to a molecule’s structure. • Vision science and links to a molecule’s structure. 14.2 Hybridization
Understandings:
• A hybrid orbital results from the mixing of different types of atomic orbitals on the same atom. Applications: • Explanation of the formation of sp3, sp2 and sp hybrid orbitals in methane, ethene and ethyne. • Identification and explanation of the relationships between Lewis (electron dot) structures, electron domains, molecular geometries and types of hybridization. Guidance: • Students need only consider species with sp3, sp2 and sp hybridization. Theory of knowledge: • Hybridization is a mathematical device which allows us to relate the bonding in a molecule to its symmetry. What is the relationship between the natural sciences, mathematics and the natural world? Which role does symmetry play in the different areas of knowledge? Topic 15: Energetics & Thermochemistry (7 hours)
15.1 Energy cycles
Understandings:
• Representative equations (eg M+(g) -> M+(aq)) can be used for enthalpy/energy of hydration, ionization, atomization, electron affinity, lattice, covalent bond and solution. • Enthalpy of solution, hydration enthalpy and lattice enthalpy are related in an energy cycle. Applications and skills: • Construction of Born-Haber cycles for group 1 and 2 oxides and chlorides. • Construction of energy cycles from hydration, lattice and solution enthalpy. For example dissolution of solid NaOH or NH4Cl in water. • Calculation of enthalpy changes from Born-Haber or dissolution energy cycles. • Relate size and charge of ions to lattice and hydration enthalpies. • Perform lab experiments which could include single replacement reactions in aqueous solutions. Guidance: • Polarizing effect of some ions producing covalent character in some largely ionic substances will not be assessed. • The following enthalpy/energy terms should be covered: ionization, atomization, electron affinity, lattice, covalent bond, hydration and solution. • Value for lattice enthalpies (section 18), enthalpies of aqueous solutions (section 19) and enthalpies of hydration (section 20) are given in the data booklet. International-mindedness: • The importance of being able to obtain measurements of something which cannot be measured directly is significant everywhere. Borehole temperatures, snow cover depth, glacier recession, rates of evaporation and precipitation cycles are among some indirect indicators of global warming. Why is it important for countries to collaborate to combat global problems like global warming? Utilization: • Other energy cycles—carbon cycle, the Krebs cycle and electron transfer in biology. 15.2 Entropy and Spontaneity
Understandings:
• Entropy (S) refers to the distribution of available energy among the particles. The more ways the energy can be distributed the higher the entropy. • Gibbs free energy (G) relates the energy that can be obtained from a chemical reaction to the change in enthalpy (ΔH), change in entropy (ΔS), and absolute temperature (T). • Entropy of gas>liquid>solid under same conditions. Applications and skills: • Prediction of whether a change will result in an increase or decrease in entropy by considering the states of the reactants and products. • Calculation of entropy changes (ΔS) from given standard entropy values (Sº). • Application of Δ𝐺𝐺° = Δ𝐻𝐻° − 𝑇𝑇Δ𝑆𝑆° in predicting spontaneity and calculation of various conditions of enthalpy and temperature that will affect this. • Relation of ΔG to position of equilibrium. Guidance: • Examine various reaction conditions that affect ΔG. • ΔG is a convenient way to take into account both the direct entropy change resulting from the transformation of the chemicals, and the indirect entropy change of the surroundings as a result of the gain/loss of heat energy. • Thermodynamic data is given in section 12 of the data booklet. International-mindedness: • Sustainable energy is a UN initiative with a goal of doubling of global sustainable energy resources by 2030. Theory of knowledge: • Entropy is a technical term which has a precise meaning. How important are such technical terms in different areas of knowledge? Topic 16: Chemical kinetics (6 hours)
16.1 Rate Expression and Reaction Mechanism
Understandings:
• Reactions may occur by more than one step and the slowest step determines the rate of reaction (rate determining step/RDS). • The molecularity of an elementary step is the number of reactant particles taking part in that step. • The order of a reaction can be either integer or fractional in nature. The order of a reaction can describe, with respect to a reactant, the number of particles taking part in the rate-determining step. • Rate equations can only be determined experimentally. • The value of the rate constant (k) is affected by temperature and its units are determined from the overall order of the reaction. • Catalysts alter a reaction mechanism, introducing a step with lower activation energy. Applications and skills: • Deduction of the rate expression for an equation from experimental data and solving problems involving the rate expression. • Sketching, identifying, and analysing graphical representations for zero, first and second order reactions. • Evaluation of proposed reaction mechanisms to be consistent with kinetic and stoichiometric data. Guidance: • Calculations will be limited to orders with whole number values. • Consider concentration–time and rate–concentration graphs. • Use potential energy level profiles to illustrate multi-step reactions; showing the higher Ea in the rate-determining step in the profile. • Catalysts are involved in the rate-determining step. • Reactions where the rate-determining step is not the first step should be considered. • Any experiment which allows students to vary concentrations to see the effect upon the rate and hence determine a rate equation is appropriate. International-mindedness: • The first catalyst used in industry was for the production of sulfuric acid. Sulfuric acid production closely mirrored a country’s economic health for a long time. What are some current indicators of a country’s economic health? Theory of knowledge: • Reaction mechanism can be supported by indirect evidence. What is the role of empirical evidence in scientific theories? Can we ever be certain in science? Utilization: • Cancer research is all about identifying mechanisms; for carcinogens as well as cancer-killing agents and inhibitors. 16.2 Activation Energy
Understandings:
• The Arrhenius equation uses the temperature dependence of the rate constant to determine the activation energy. • A graph of 1/T against ln k is a linear plot with gradient – Ea / R and intercept, lnA. • The frequency factor (or pre-exponential factor) (A) takes into account the frequency of collisions with proper orientations. Applications and skills: • Analysing graphical representation of the Arrhenius equation in its linear form • Describing the relationships between temperature and rate constant; frequency factor and complexity of molecules colliding. • Determining and evaluating values of activation energy and frequency factors from data. Guidance: • Use energy level diagrams to illustrate multi-step reactions showing the RDS in the diagram. • Consider various data sources in using the linear expression Utilization: • The flashing light of fireflies is produced by a chemical process involving enzymes. • The relationship between the “lock and key” hypothesis of enzymes and the Arrhenius equation. Topic 17: Equilibrium (4 hours)
17.1 The Equilibrium Law
Understandings:
• Le Châtelier’s principle for changes in concentration can be explained by the equilibrium law. • The position of equilibrium corresponds to a maximum value of entropy and a minimum in the value of the Gibbs free energy. • The Gibbs free energy change of a reaction and the equilibrium constant can both be used to measure the position of an equilibrium reaction and are related by the equation, ΔG = -RTlnK . Applications and skills: • Solution of homogeneous equilibrium problems using the expression for Kc. • Relationship between ΔG and the equilibrium constant. • Calculations using the equation ΔG = -RTlnK . Guidance: • The expression ΔG = -RTlnK is given in the data booklet in section 1. • Students will not be expected to derive the expression ΔG = -RTlnK • The use of quadratic equations will not be assessed. Theory of knowledge: • The equilibrium law can be deduced by assuming that the order of the forward and backward reaction matches the coefficients in the chemical equation. What is the role of deductive reasoning in science? • We can use mathematics successfully to model equilibrium systems. Is this because we create mathematics to mirror reality or because the reality is intrinsically mathematical? • Many problems in science can only be solved when assumptions are made which simplify the mathematics. What is the role of intuition in problem solving? Utilization: • The concept of a closed system in dynamic equilibrium can be applied to a range of systems in the biological, environmental and human sciences. Topic 18: Acids and Bases (10 hours)
18.1 Lewis Acids and Bases
Understandings:
• A Lewis acid is a lone pair acceptor and a Lewis base is a lone pair donor. • When a Lewis base reacts with a Lewis acid a coordinate bond is formed. • A nucleophile is a Lewis base and an electrophile is a Lewis acid. Applications and skills: • Application of Lewis’ acid–base theory to inorganic and organic chemistry to identify the role of the reacting species. Guidance: • Both organic and inorganic examples should be studied. • Relations between Brønsted–Lowry and Lewis acids and bases should be discussed. International-mindedness: • Acid–base theory has developed from the ideas of people from different parts of the world through both collaboration and competition. Theory of knowledge: • The same phenomenon can sometimes be explored from different perspectives, and explained by different theories. For example, do we judge competing theories by their universality, simplicity or elegance? 18.2 Calculations involving acids and bases
Understandings:
• The expression for the dissociation constant of a weak acid (Ka) and a weak base (Kb). • For a conjugate acid base pair, Ka × Kb = Kw. • The relationship between Ka and pKa is (pKa = -log Ka), and between Kb and pKb is (pKb = -log Kb). Applications and skills: • Solution of problems involving [H+ (aq)], [OH–(aq)], pH, pOH, Ka, pKa, Kb and pKb. • Discussion of the relative strengths of acids and bases using values of Ka, pKa, Kb and pKb. Guidance: • The value Kw depends on the temperature. • The calculation of pH in buffer solutions will only be assessed in options B.7 and D.4. • Only examples involving the transfer of one proton will be assessed. • Calculations of pH at temperatures other than 298 K can be assessed. • Students should state when approximations are used in equilibrium calculations. • The use of quadratic equations will not be assessed. International-mindedness: • Mathematics is a universal language. The mathematical nature of this topic helps chemists speaking different native languages to communicate more objectively. 18.3 pH Curves
Understandings:
• The characteristics of the pH curves produced by the different combinations of strong and weak acids and bases. • An acid–base indicator is a weak acid or a weak base where the components of the conjugate acid–base pair have different colours. • The relationship between the pH range of an acid–base indicator, which is a weak acid, and its pKa value. • The buffer region on the pH curve represents the region where small additions of acid or base result in little or no change in pH. • The composition and action of a buffer solution. Applications and skills: • The general shapes of graphs of pH against volume for titrations involving strong and weak acids and bases with an explanation of their important features. • Selection of an appropriate indicator for a titration, given the equivalence point of the titration and the end point of the indicator. • While the nature of the acid–base buffer always remains the same, buffer solutions can be prepared by either mixing a weak acid/base with a solution of a salt containing its conjugate, or by partial neutralization of a weak acid/base with a strong acid/base. • Prediction of the relative pH of aqueous salt solutions formed by the different combinations of strong and weak acid and base. Guidance: • Only examples involving the transfer of one proton will be assessed. Important features are: – intercept with pH axis – equivalence point – buffer region – points where pKa = pH or pKb = pOH. • For an indicator which is a weak acid: – HIn(aq) H+(aq) + In-(aq) Colour A Colour B – The colour change can be considered to take place over a range of p Ka ± 1. • For an indicator which is a weak base: – BOH(aq) B+(aq) + OH-(aq) Colour A Colour B • Examples of indicators are listed in the data booklet in section 22. • Salts formed from the four possible combinations of strong and weak acids and bases should be considered. Calculations are not required. • The acidity of hydrated transition metal ions is covered in topic 13. The treatment of other hydrated metal ions is not required. Theory of knowledge: • Is a pH curve an accurate description of reality or an artificial representation? Does science offer a representation of reality? Topic 19: Redox Processes (6 hours)
19.1 Electrochemical Cells
Understandings:
• A voltaic cell generates an electromotive force (EMF) resulting in the movement of electrons from the anode (negative electrode) to the cathode (positive electrode) via the external circuit. The EMF is termed the cell potential (Eº). • The standard hydrogen electrode (SHE) consists of an inert platinum electrode in contact with 1 mol dm-3 hydrogen ion and hydrogen gas at 100 kPa and 298 K. The standard electrode potential (Eº) is the potential (voltage) of the reduction half-equation under standard conditions measured relative to the SHE. Solute concentration is 1 mol dm-3 or 100 kPa for gases. Eº of the SHE is 0 V. • When aqueous solutions are electrolysed, water can be oxidized to oxygen at the anode and reduced to hydrogen at the cathode. • When Eº is positive, Gº is negative indicative of a spontaneous process. When Eº is negative, Gº is positive indicative of a non-spontaneous process. When Eº is 0, then Gº is 0. • Current, duration of electrolysis and charge on the ion affect the amount of product formed at the electrodes during electrolysis. • Electroplating involves the electrolytic coating of an object with a metallic thin layer. Applications and skills: • Calculation of cell potentials using standard electrode potentials. • Prediction of whether a reaction is spontaneous or not using Eo values. • Determination of standard free-energy changes (ΔGo) using standard electrode potentials. • Explanation of the products formed during the electrolysis of aqueous solutions. • Perform lab experiments that could include single replacement reactions in aqueous solutions. • Determination of the relative amounts of products formed during electrolytic processes. • Explanation of the process of electroplating. Guidance: • Electrolytic processes to be covered in theory should include the electrolysis of aqueous solutions (eg sodium chloride, copper(II) sulfate etc) and water using both inert platinum or graphite electrodes and copper electrodes. Explanations should refer to Eº values, nature of the electrode and concentration of the electrolyte. • Δ𝐺𝐺° = −𝑛𝑛𝑛𝑛𝑛𝑛° is given in the data booklet in section 1. • Faraday’s constant = 96 500 C mol-1 is given in the data booklet in section 2. • The term “cells in series” should be understood. International-mindedness: • Many electrochemical cells can act as energy sources alleviating the world’s energy problems but some cells such as super-efficient microbial fuel cells (MFCs) (also termed biological fuel cells) can contribute to clean-up of the environment. How do national governments and the international community decide on research priorities for funding purposes? Theory of knowledge: • The SHE is an example of an arbitrary reference. Would our scientific knowledge be the same if we chose different references? Utilization: • Electroplating. • Electrochemical processes in dentistry. • Rusting of metals. Topic 20: Organic chemistry (12 hours)
20.1 Types of Organic Reactions
Understandings:
Nucleophilic Substitution Reactions: • SN1 represents a nucleophilic unimolecular substitution reaction and SN2 represents a nucleophilic bimolecular substitution reaction. SN1 involves a carbocation intermediate. SN2 involves a concerted reaction with a transition state. • For tertiary halogenoalkanes the predominant mechanism is SN1 and for primary halogenoalkanes it is SN2. Both mechanisms occur for secondary halogenoalkanes. • The rate determining step (slow step) in an SN1 reaction depends only on the concentration of the halogenoalkane, rate = k[halogenoalkane]. For SN2, rate = k[halogenoalkane][nucleophile]. SN2 is stereospecific with an inversion of configuration at the carbon. • SN2 reactions are best conducted using aprotic, non-polar solvents and SN1 reactions are best conducted using protic, polar solvents. Electrophilic Addition Reactions: • An electrophile is an electron-deficient species that can accept electron pairs from a nucleophile. Electrophiles are Lewis acids. • Markovnikov’s rule can be applied to predict the major product in electrophilic addition reactions of unsymmetrical alkenes with hydrogen halides and interhalogens. The formation of the major product can be explained in terms of the relative stability of possible carbocations in the reaction mechanism. Electrophilic Substitution Reactions: • Benzene is the simplest aromatic hydrocarbon compound (or arene) and has a delocalized structure of π bonds around its ring. Each carbon to carbon bond has a bond order of 1.5. Benzene is susceptible to attack by electrophiles. Reduction Reactions: • Carboxylic acids can be reduced to primary alcohols (via the aldehyde). Ketones can be reduced to secondary alcohols. Typical reducing agents are lithium aluminium hydride (used to reduce carboxylic acids) and sodium borohydride. Applications and skills: Nucleophilic Substitution Reactions: • Explanation of why hydroxide is a better nucleophile than water. • Deduction of the mechanism of the nucleophilic substitution reactions of halogenoalkanes with aqueous sodium hydroxide in terms of SN1 and SN2 mechanisms. Explanation of how the rate depends on the identity of the halogen (ie the leaving group), whether the halogenoalkane is primary, secondary or tertiary and the choice of solvent. • Outline of the difference between protic and aprotic solvents. Electrophilic Addition Reactions: • Deduction of the mechanism of the electrophilic addition reactions of alkenes with halogens/interhalogens and hydrogen halides. Electrophilic Substitution Reactions: • Deduction of the mechanism of the nitration (electrophilic substitution) reaction of benzene (using a mixture of concentrated nitric acid and sulfuric acid). Reduction Reactions: • Writing reduction reactions of carbonyl containing compounds: aldehydes and ketones to primary and secondary alcohols and carboxylic acids to aldehydes, using suitable reducing agents. • Conversion of nitrobenzene to phenylamine via a two-stage reaction. Guidance: • Reference should be made to heterolytic fission for SN1 reactions. • The difference between homolytic and heterolytic fission should be understood. • The difference between curly arrows and fish-hooks in reaction mechanisms should be emphasized. • Use of partial charges (δ+ and δ-) and wedge-dash three-dimensional representations (using tapered bonds as shown below) should be encouraged where appropriate in explaining reaction mechanisms. • Typical conditions and reagents of all reactions should be known (eg catalysts, reducing agents, reflux etc.). However, more precise details such as specific temperatures need not be included. International-mindedness: • What role does green and sustainable chemistry, in relation to organic chemistry, play in a global context? Utilization: • Organic synthesis plays a vital role in drug design and drug uptake in medicine and biochemistry. • Nutrition, food science and biotechnology also are underpinned by organic chemistry. 20.2 Synthetic Routes
Understandings:
• The synthesis of an organic compound stems from a readily available starting material via a series of discrete steps. Functional group interconversions are the basis of such synthetic routes. • Retro-synthesis of organic compounds. Applications and skills: • Deduction of multi-step synthetic routes given starting reagents and the product(s). Guidance: • Conversions with more than four stages will not be assessed in synthetic routes. • Reaction types can cover any of the reactions covered in topic 10 and sub-topic 20.1. International-mindedness: • How important are natural products to developing countries? Explore some specific examples of natural products available in developing countries which are important to the developed world. Theory of knowledge: • A retro-synthetic approach is often used in the design of synthetic routes. What are the roles of imagination, intuition and reasoning in finding solutions to practical problems? Utilization: • Natural products are compounds isolated from natural sources and include taxol, mescaline and capsaicin. 20.3 Stereoisomerism
Understandings:
• Stereoisomers are subdivided into two classes—conformational isomers, which interconvert by rotation about a σ bond and configurational isomers that interconvert only by breaking and reforming a bond. Configurational isomers are further subdivided into cis-trans and E/Z isomers and optical isomers. • Cis-trans isomers can occur in alkenes or cycloalkanes (or heteroanalogues) and differ in the positions of atoms (or groups) relative to a reference plane. According to IUPAC, E/Z isomers refer to alkenes of the form R1R2C=CR3R4 (R1 ≠ R2, R3 ≠ R4) where neither R1 nor R2 need be different from R3 or R4. • A chiral carbon is a carbon joined to four different atoms or groups. • An optically active compound can rotate the plane of polarized light as it passes through a solution of the compound. Optical isomers are enantiomers. Enantiomers are non-superimposeable mirror images of each other. Diastereomers are not mirror images of each other. • A racemic mixture (or racemate) is a mixture of two enantiomers in equal amounts and is optically inactive. Applications and skills: • Construction of 3-D models (real or virtual) of a wide range of stereoisomers. • Explanation of stereoisomerism in non-cyclic alkenes and C3 and C4 cycloalkanes. • Comparison between the physical and chemical properties of enantiomers. • Description and explanation of optical isomers in simple organic molecules. • Distinction between optical isomers using a polarimeter. Guidance: • The term geometric isomers as recommended by IUPAC is now obsolete and cis-trans isomers and E/Z isomers should be encouraged in the teaching programme. • In the E/Z system, the group of highest Cahn–Ingold–Prelog priority attached to one of the terminal doubly bonded atoms of the alkene (ie R1 or R2) is compared with the group of highest precedence attached to the other (ie R3 or R4). The stereoisomer is Z if the groups lie on the same side of a reference plane passing through the double bond and perpendicular to the plane containing the bonds linking the groups to the double-bonded atoms; the other stereoisomer is designated as E. • Wedge-dash type representations involving tapered bonds should be used for representations of optical isomers. International-mindedness: • Have drugs and medicines in some countries been sold and administered as racemates instead of as the desired enantiomer with the associated therapeutic activity? Can you think of any drugs or medicines which may serve as good case studies for this? Theory of knowledge: • The existence of optical isomers provide indirect evidence for a tetrahedrally bonded carbon atom. Which ways of knowing allow us to connect indirect evidence to our theories? • Stereoisomerism can be investigated by physical and computer models. What is the role of such models in other areas of knowledge? • One of the challenges for the scientist and the artist is to represent the threedimensional world in two dimensions. What are the similarities and differences in the two approaches? What is the role of the different ways of knowing in the two approaches? Utilization: • Many of the drugs derived from natural sources are chiral and include nicotine, dopamine, thyroxine and naproxen. • The role of stereochemistry in vision science and food science. • In many perfumes, stereochemistry often can be deemed more important than chemical composition. Topic 21: Measurement and analysis (2 hours)
21.1 Spectroscopic Identification of Organic Compounds
Understandings:
• Structural identification of compounds involves several different analytical techniques including IR, 1H NMR and MS. • In a high resolution 1H NMR spectrum, single peaks present in low resolution can split into further clusters of peaks. • The structural technique of single crystal X-ray crystallography can be used to identify the bond lengths and bond angles of crystalline compounds. Applications and skills: • Explanation of the use of tetramethylsilane (TMS) as the reference standard. • Deduction of the structure of a compound given information from a range of analytical characterization techniques (X-ray crystallography, IR, 1H NMR and MS). Guidance: • Students should be able to interpret the following from 1H NMR spectra: number of peaks, area under each peak, chemical shift and splitting patterns. Treatment of spin-spin coupling constants will not be assessed but students should be familiar with singlets, doublets, triplets and quartets. • High resolution 1H NMR should be covered. • The precise details of single crystal X-ray crystallography need not be known in detail, but students should be aware of the existence of this structural technique in the wider context of structural identification of both inorganic and organic compounds. • The operating principles are not required for any of these methods. International-mindedness: • The chemical community often shares chemical structural information on the international stage. The Cambridge Crystallographic Database, ChemSpider developed by the Royal Society of Chemistry and the Protein Data Bank (RCSB PDB) (at Brookhaven National Laboratory, USA) are examples which highlight the international nature of the scientific community. Theory of knowledge: • The intensity ratio of the lines in the high resolution NMR spectrum is given by the numbers in Pascal's triangle, a mathematical pattern known independently over a thousand years ago by a number of different cultures. Why is mathematics such an effective tool in science? Is mathematics the science of patterns? Utilization: • Protons in water molecules within human cells can be detected by magnetic resonance imaging (MRI), giving a three-dimensional view of organs in the human body. Why is MRI replacing computerized tomography (CT) scans for some applications but is used as a complementary technique for others? • MS (and other techniques such as TLC, GC, GC-MS and HPLC) can be used in forensic investigations at crime scenes. • Analytical techniques can be used to test for drug abuse by high-performance athletes. |