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This comprehensive guide covers key concepts in organic chemistry, including alkenes, polymers, and nuclear magnetic resonance (nmr) spectroscopy. it provides detailed explanations, examples, and practice questions to help students master these topics. Particularly useful for a-level chemistry students preparing for exams, offering a structured approach to understanding complex chemical structures and reactions.
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What is an alkene and its general formula? It is an unsaturated hydrocarbon with a least one C=C bond. General formula is CnH2n What is a sigma bond? σ single covalent bond formed when two s orbitals overlap. High electron density What is a pi bond? sideways overlap of p orbitals that occur in a double or triple bond. Much weaker than sigma, low bond enthalpy and lower electrostatic attraction Is an alkane or an alkene more reactive? Alkene. contains both sigma and pi bonds with high electron density and low bond enthalpy. Define steroisomers have the same structural formulae but have a different arrangement of atoms in a space What is a cis isomer? (Z) the two Xs are on the same side of the double bond What is a trans isomer? (E) the two x's are on opposite sides of the double bond What is an electrophile? An electron pair acceptor What is a nucleophile? An electron pair donor How do you produce alkanes from an alkene? React with hydrogen gas in addition reaction. requires nickle catalyst and 150 ℃ How do you produce dihaloalkanes from alkenes? Halogens react with alkenes in electrophillic addition. Bromine water turns orange to colourless as it is added across the double bond to form a colour dibromoalkane How do you produce alcohols from alkenes? Alkenes need to be hydrated by steam at 300 ℃ and pressure 60 - 70 atm. Needs solid phosphoric (V) acid catalyst How do you form haloalkanes from alkenes? Alkenes undergo addition with hydrogen halides
What is Markownikoffs rule? The major product from addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached How do you find the monomer of a polymer? Take the repeat unit and add a double bond State an advantage of polymers Very unreactive so food doesn't react with the coating on pans, plastic windows don't rot, etc. State a disadvantage of polymers Most polymers aren't biodegradable and therefore difficult to dispose of. This leads to more environmental damage. State the ways of dealing with waste plastics Burning as a fuel Burying in landfill Remoulding for new objects Cracking in monomers to become feedstock for new plastics or other chemicals State two types of polymers that aren't wasteful (Ecofriendly) Biodegradable (eaten by other microorganisms) Photodegradable (Broken down by sunlight) What is nuclear magnetic resonance (NMR)? Analytical technique used to work out the structure of an organic molecule What are the basics of NMR?
Relative area underneath each peak tells you the relative number of H atoms in each environment. Areas can be shown using numbers above the peaks or with an integration trace What is the difference between carbon - 13 and interpreting proton NMR? Peaks in the spectrum split according to how the hydrogen environments are arranged. What is spin-spin coupling? Caused by influence of hydrogen atoms that are bonded to neighbouring carbons, only hydrogen nuclei on adjacent carbon atoms affect each other. these split peaks are called mutliplets and always split into one more that the no. of H atoms on neighbouring C atoms. What is the n + 1 rule? these split peaks are called multiplets and always split into one more that the no. of H atoms on neighbouring C atoms. How can you work out the number of neighbouring hydrogens? By looking at how many the peaks split into:
C6H6, cyclic structure. Kekule model and delocalised model What are the 3 key points that do not support the kekule model?
How does phenol react with bases and sodium? Weak acid so will undergo typical acid base reactions
melting point of crystals and compare it against known melting point to identify carbonyl compounds. What is the test to determine whether something is an aldehyde or ketone? Tollens' reagent is colourless solution of silver nitrate dissolved in aq ammonia. When heated in a test tube, aldehydes are oxidised and a silver mirror is formed from the silver ions being reduced to silver. Ketones show no change Prefix / suffix and example of Alkanes -ane propane - CH3CH2CH Prefix / suffix and example of branched alkanes alkyl-(-yl) methylpropane - CH3CH(CH3)CH Prefix / suffix and example of alkenes -ene propene - CH3CH=CH Prefix / suffix and example of haloalkanes chloro - / bromo - / iodo - chloroethane - CH3CH2Cl Prefix / suffix and example of alcohols
places will absorb at different frequencies IR spectrometre produces a spectrum that shows what frequencies of radiation is being absorbed by molecules, can be used to identify functional groups How do you use a mass spectrometer to find relative molecular mass? To find relative molecular mass of a compound you look at molecular ion peak (M peak). mass / charge value of molecular ion peak is molecular mass mass / charge = m / z What are fragments on a mass spectrum? Ions of a molecular ion, can be used to identify molecules and their structure. Only ions show on mass spectrum as other free radicals are lost How can you use a mass spectrometer to work out structural formula?
Hydrolyse more easily with a base than an acid to form dicarboxylic acid salt and diol. How are polyamides formed? Dicarboxylic acids and diamines Carboxyl (-COOH) groups react with amino (-NH2) to form amide (-CONH). H2O is lost each time amide link it formed (condensation reaction) and forms polyamide How are polyesters formed? Dicarboxylic acids and diols Carboxyl (-COOH) groups react with hydroxyl (-OH) to form ester links (-COO-). Another condensation reaction and polymer formed is a polyester. How do you find the monomer of a condensation polymer? First find the amide (HN-CO) or ester (CO-O) link and break it down the model then add an H or OH to both ends of both molecules to find the monomers What happens to a molecule that contains both an amine and an alcohol group? Can react with dicarboxylic acid in condensation polymerisation reactions and the polymers they form contain both amine and ester links. What happens if a molecule contains a carboxylic acid group and either an alcohol or amine? Can polymerise with itself to form a condensation polymer with only one monomer