Organic chemistry

Give the IUPAC name of CH₃CH(CH₃)CH₂CH₂OH.

Write a condensed structural formula for 3-ethyl-2-methylhexane.

A compound has condensed formula CH₃C(CH₃)₂CH₂CH(OH)CH₃. Give its IUPAC name and molecular formula.

In the first step of attack by :NH₃ on a positive carbon centre, state where the bond-forming curly arrow starts and ends.

Write the radical propagation step in which a methyl radical reacts with chlorine, and explain the required dot-and-arrow notation.

A student draws hydroxide attacking CH₃CH₂I with one curly arrow from carbon to oxygen and a second from iodine to the C–I bond. Correct both arrows and identify the electron source in each case.

Butan-1-ol and butan-2-ol have the same molecular formula. State their type of isomerism.

At the left carbon of a C=C bond the groups are H and CH₃; at the right carbon they are CH₃ and CH₂CH₃. The left CH₃ and right CH₂CH₃ groups are drawn on opposite sides. Assign E or Z and justify your choice using CIP priorities.

Draw or give condensed structural formulae for every aldehyde and ketone with molecular formula C₄H₈O. Name each one and classify the relationship between the aldehydes and the ketone.

State the physical property used to separate crude oil into fractions and name the separation process.

Explain why a C₅ alkane is collected nearer the top of a fractionating column than a C₁₅ alkane.

A vapour mixture contains C₇H₁₆, C₁₂H₂₆ and C₁₈H₃₈. Predict their order of condensation from highest to lowest in the column, and explain why separating them does not change any molecular formula.

Complete and balance this cracking equation: $\mathrm{C_{12}H_{26}\rightarrow C_8H_{18}+X}$.

A refinery cracks C₁₅H₃₂ to one molecule of C₈H₁₈, one of C₃H₆ and ethene only. Determine the number of ethene molecules formed, then explain the economic purpose of this conversion.

Compare the conditions and main product emphasis of thermal cracking with catalytic cracking.

Write the balanced equation for the complete combustion of propane.

In a catalytic converter, carbon monoxide reacts with nitrogen monoxide. Write a balanced equation and state which pollutant is oxidised and which is reduced.

A flue gas contains 1.60 kg of SO₂. Calculate the minimum mass of CaCO₃ needed for complete removal using $\mathrm{CaCO_3+SO_2\rightarrow CaSO_3+CO_2}$. Use $M_r(\mathrm{SO_2})=64.1$ and $M_r(\mathrm{CaCO_3})=100.1$.

Write the initiation step for methane chlorination and state the bond-fission type.

Write both propagation equations that convert methane and chlorine into chloromethane during free-radical substitution.

Give three different termination equations available in methane chlorination, and explain why prolonged irradiation lowers the purity of chloromethane.

Name the organic product when 1-bromopropane undergoes nucleophilic substitution with CN^−.

Outline the one-step mechanism for CH₃CH₂CH₂Br reacting with OH^−, including both curly arrows and the products.

A labelled set contains 1-chlorobutane (A), 1-bromobutane (B) and 1-iodobutane (C). Each is hydrolysed at the same concentration and temperature. Predict the rate order and explain why bond enthalpy, rather than C–X bond polarity, controls it.

State the organic product of eliminating HBr from 2-bromopropane and name the role of OH^−.

Two samples of 1-bromopropane are heated separately with aqueous KOH and ethanolic KOH. Give the principal organic product in each case and explain the different roles played by OH^−.

2-bromobutane is heated with ethanolic potassium hydroxide. Name the two structurally isomeric alkene products, without counting E/Z forms separately, and state the three electron-pair movements in the elimination step.

State why ozone in the upper atmosphere is beneficial.

Combine the two chlorine-radical ozone steps to obtain the overall equation, and identify the catalyst and intermediate.

For the CFC CF₂Cl₂, write a UV photodissociation equation that releases a chlorine radical, then explain why a low concentration of this CFC can cause extensive ozone loss.

Define an unsaturated hydrocarbon and state the feature that makes ethene unsaturated.

Ethene and ethane both contain carbon–carbon bonding. State the additional bonding feature in ethene and explain how it changes electron density and reactivity.

Explain, using electron density and bond changes, why an alkene reacts readily with an electrophile to form an addition product.

State the observation when bromine water is shaken with cyclohexene and name the organic product.

Outline the electrophilic-addition mechanism that gives the major product when propene reacts with HBr. Include the two curly arrows, intermediate and product.

2-methylbut-2-ene reacts with HBr. Name the major and minor structural products and explain their relative amounts by comparing the carbocation intermediates.

2-Methylpropene has the structure CH₂=C(CH₃)₂. Give the displayed repeat unit of its addition polymer.

A polymer segment is -CH₂-CH(CN)-CH₂-CH(CN)-. Deduce the monomer, name the addition polymer and state the strongest intermolecular force between its chains.

Unplasticised PVC is rigid, whereas PVC containing a molecular plasticiser bends more readily. Explain both observations using the structure of poly(chloroethene), intermolecular forces and chain movement. Also explain why neither sample is readily hydrolysed.

Write the equation for fermentation of glucose to ethanol and state two conditions that keep the yeast working effectively.

Propene is converted into propan-2-ol using steam and an acid catalyst. Outline the three mechanistic stages and explain why the catalyst is unchanged overall.

A fermenter produces $92.0\,\text{kg}$ of ethanol. Complete combustion releases all of its carbon as CO₂. Calculate the CO₂ mass using C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, then assess whether describing the fuel as carbon neutral is justified.

Butan-2-ol is warmed with acidified potassium dichromate(VI). Name the organic product and state the colour change.

Give the reagent, apparatus choice and an equation using [O] for converting 2-methylpropan-1-ol into 2-methylpropanal without producing much 2-methylpropanoic acid. State the aldehyde's results with Tollens' reagent and Fehling's solution.

Three C₄H₁₀O alcohols are butan-1-ol, butan-2-ol and 2-methylpropan-2-ol. Predict the organic result when each is heated under reflux with excess acidified dichromate(VI), and give a chemical test that distinguishes the two oxidation products.

Give the organic product and reaction type when ethanol vapour is heated with an acid catalyst and loses water.

List all structural alkene products formed by dehydrating 3-methylpentan-3-ol and explain why more than one structural product is possible.

Outline the acid-catalysed elimination mechanism that converts cyclohexanol into cyclohexene. State the origin and destination of each curly arrow and explain how the product could become a polymer feedstock without using an alkene obtained directly from crude oil.

A colourless liquid may contain a C=C bond. State a test-tube reagent and the positive observation.

Describe two separate test-tube tests that identify which of two bottles contains ethanal and which contains ethanoic acid. Include every positive observation.

Four unlabelled samples are ethanol, ethanal, ethene and ethanoic acid. Design a shortest reliable test sequence using reagents from the specification, and state the observation that assigns each sample.

Calculate the precise molecular mass of C₂H₄O using ¹²C = 12.00000, ¹H = 1.00783 and ¹⁶O = 15.99491.

A compound containing only C, H and O has a high-resolution molecular-ion mass of $74.0369$. Choose between C₄H₁₀O and C₃H₆O₂. Use ¹²C = 12.00000, ¹H = 1.00783 and ¹⁶O = 15.99491.

An unknown has measured molecular-ion mass $88.0526$. Candidate formulas are C₄H₈O₂ and C₅H₁₂O. Calculate both precise masses, identify the formula and calculate the absolute error of the chosen value. Use ¹²C = 12.00000, ¹H = 1.00783 and ¹⁶O = 15.99491.

An IR spectrum has a strong absorption at 1718 cm^-1. Use the Data Booklet to identify the bond indicated by this absorption.

A liquid's IR spectrum contains a strong peak at 1740 cm^-1, no broad O-H absorption, and a fingerprint region identical to a reference spectrum of ethyl ethanoate. Deduce the compound and explain the purpose of the fingerprint comparison.

A nominally pure propanone sample matches the propanone reference fingerprint and has a strong C=O absorption, but it also shows a broad absorption at 3200-3550 cm^-1. Suggest an impurity and explain how IR absorption by CO₂, CH₄ and water vapour contributes to global warming.

Identify the chiral carbon in CH₃CH(OH)CH₂CH₃ and name the compound.

Describe how to draw the two enantiomers of 2-bromobutane using wedge-and-dash bonds, and state their relationship and effect on plane-polarised light.

Ethanal and propanone each react with HCN. Explain why one product is a racemic mixture but the other is optically inactive, naming both hydroxynitrile products.

Butanal is treated with aqueous sodium tetrahydridoborate. Name the organic product and write an equation using [H].

Two bottles contain pentanal and pentan-3-one. For Tollens' reagent and Fehling's solution, state the conditions and the observation expected with each bottle.

Butan-2-one reacts with KCN followed by dilute acid. Name the mechanism and organic product, outline both electron-pair movements before protonation, explain the stereochemical composition and state the main KCN hazard.

Name the ester made from propan-1-ol and ethanoic acid, state the catalyst and write the equation using condensed structures.

Methyl propanoate is heated with excess aqueous sodium hydroxide. Name both organic products, write the equation and explain why the carboxylic-acid product is not isolated directly from this mixture.

A triglyceride has $M_r=890$. Calculate the minimum mass of NaOH needed to hydrolyse $17.8\,\text{g}$ completely, then state the two types of organic product. Use $M_r(\mathrm{NaOH})=40.0$.

Ethanoyl chloride is added to ethanol. Name both products and state one visible observation.

Propanoyl chloride reacts with excess methylamine. Name the amide and salt formed, and outline the addition-elimination steps.

Aspirin manufacture can use ethanoic anhydride or ethanoyl chloride as the acylating agent. The desired aspirin has $M_r=180$; the anhydride route also makes ethanoic acid, $M_r=60.0$, while the chloride route also makes HCl, $M_r=36.5$. Calculate each route's atom economy and explain why industry can still prefer the anhydride route.

Describe the shape, carbon-carbon bond lengths and pi bonding in a benzene molecule.

Hydrogenation of cyclohexene has $\Delta H=-121\,\text{kJ mol}^{-1}$, while hydrogenation of benzene to cyclohexane has $\Delta H=-207\,\text{kJ mol}^{-1}$. Calculate the extra stability of benzene relative to a ring with three isolated C=C bonds.

A student claims benzene is cyclohexa-1,3,5-triene with fixed alternating bonds. Evaluate the claim using measured C-C bond lengths of $0.140\,\text{nm}$ in benzene, $0.154\,\text{nm}$ for a C-C bond and $0.134\,\text{nm}$ for a C=C bond, then use delocalisation to explain why substitution is preferred to addition.

State the two reagents for nitrating benzene, name the catalyst and identify the electrophile.

Benzene reacts with propanoyl chloride in the presence of anhydrous AlCl₃. Name the organic product, write the overall equation and identify the attacking electrophile.

Outline the complete electrophilic-substitution mechanism for reacting benzene with ethanoyl chloride and anhydrous AlCl₃. Include electrophile generation, both ring electron movements and catalyst regeneration.

Name a reagent and a condition used to convert 1-bromopropane into propylamine while limiting further substitution.

A two-stage route changes bromoethane into propylamine. Give the reagent and condition for each stage and name the intermediate.

Describe how nitrobenzene can be converted into a pure sample of phenylamine. Include the purpose of the final alkaline treatment.

Write an equation showing ethylamine acting as a base in water.

Place ethylamine, ammonia and phenylamine in decreasing order of base strength. Explain both differences in the order.

A student claims that phenylamine should be the strongest base because its nitrogen atom is attached to a large electron-rich ring. Evaluate this claim and predict which of phenylamine and propylamine forms the greater concentration of hydroxide ions in equally concentrated aqueous solutions.

State the feature of an amine molecule that allows it to act as a nucleophile.

Ethylamine reacts with ethanoyl chloride. Name the organic product, state the mechanism type and describe the two essential curly arrows in the addition step.

An excess of 1-bromobutane is heated with butylamine. Predict the final nitrogen-containing product, explain why several substitution stages can occur, and relate one structural feature of the final ion to its use in a cationic surfactant.

Name the linkage formed when a dicarboxylic acid reacts with a diamine, and name the small molecule eliminated when the acid itself is used.

Hexane-1,6-diamine reacts with hexanedioic acid. Give the condensed formula of the polyamide repeat unit and identify the strongest intermolecular force between its chains.

A polymer contains the repeating segment [–O–CH₂CH₂–O–CO–C₆H₄–CO–]_n, with the two carbonyl groups bonded at positions 1 and 4 of the benzene ring. Deduce both monomers, classify the polymer, and explain why its chains attract one another even though it has no N–H bonds.

Explain why a polyalkene chain is much less susceptible to hydrolysis than a polyester chain.

A disposable article can be made from a polyamide or from poly(propene). Compare their likely biodegradability using their chain structures.

A council is choosing between landfill, mechanical recycling and energy-recovery incineration for mixed polymer waste. Evaluate the three options and justify why sorting the waste can change the best choice.

Define the term zwitterion and state its overall charge.

Give the displayed ionic forms of alanine, CH₃CH(NH₂)COOH, in strongly acidic solution and in strongly alkaline solution.

A solution contains the zwitterion of 2-aminobutanoic acid. Write net ionic equations for its separate reactions with H⁺ and OH⁻, and identify the role of the zwitterion in each reaction.

State what determines the primary structure of a protein.

Glycine reacts with alanine so that the carboxyl group of glycine bonds to the amino group of alanine. Give the condensed structure of the dipeptide, name the new linkage and state the other product.

A tripeptide is hydrolysed completely to glycine, cysteine and alanine. Explain what happens to its peptide links, state two interactions that can maintain tertiary structure in proteins, and calculate the $R_f$ of an amino-acid spot that moves $38\,\text{mm}$ when the solvent front moves $64\,\text{mm}$.

State why an enzyme is described as a catalyst.

Explain why one enantiomer of a chiral substrate can bind to an enzyme active site much more strongly than the other enantiomer.

A proposed drug resembles the transition-state shape of an enzyme's normal substrate. Explain how it could inhibit the enzyme, why stereochemistry must be considered, and how computer modelling can reduce the number of compounds synthesised.

Name the three types of component present in a DNA nucleotide.

One DNA strand contains the base sequence A–C–G–T–T–A. Give the complementary sequence and distinguish the bonding along a strand from the bonding between the strands.

A short double-stranded DNA section has eight A–T base pairs and eleven C–G base pairs. It is heated until the strands separate. State the number of hydrogen bonds broken and explain why a section with a greater proportion of C–G pairs generally needs more energy to separate.

Name the DNA base to which cisplatin bonds and identify the donor atom in that base.

Explain, using ligand replacement and DNA structure, how cisplatin can stop a cancer cell from replicating.

Cisplatin reduces tumour growth but can damage bone marrow and the digestive lining. Explain both observations and state why treatment decisions must balance benefit against adverse effects.

Give two reasons, other than cost, why a chemist may prefer a high-atom-economy synthesis with fewer reaction steps.

Devise a three-step synthesis of ethanoic acid starting from ethene. Give the reagent and condition for each step and name the intermediate after each of the first two steps.

Starting from bromoethane and using no more than three reaction steps, prepare N-propylethanamide. Give structures or names of both intermediates, reagents, conditions and the reason the first step changes the carbon-chain length.

Give two properties that make tetramethylsilane suitable as the standard for chemical shift in NMR spectroscopy.

A compound gives three ¹H NMR signals: a triplet with integration 3, a singlet with integration 3 and a quartet with integration 2. Explain the splitting and deduce a structure consistent with molecular formula C₄H₈O₂.

An ester has molecular formula C₅H₁₀O₂ and five ¹³C NMR signals. Its ¹H NMR spectrum contains two triplets, each integrating to 3, and two quartets, each integrating to 2; one quartet is substantially further downfield than the other. Deduce the ester and justify every signal pattern.

On a TLC plate, a spot travels $4.5\,\text{cm}$ from the start line while the solvent front travels $7.5\,\text{cm}$. Calculate the $R_f$ value.

Two dyes are placed on the same TLC plate. Dye P is very soluble in the solvent and weakly retained by the coating; dye Q is less soluble and more strongly retained. Predict which dye has the larger $R_f$ and explain your answer.

A GC trace of a flavour mixture has peaks at $2.8$, $4.6$ and $7.1\,\text{min}$. Under identical conditions, reference compounds X, Y and Z have retention times $2.8$, $4.6$ and $6.9\,\text{min}$ respectively. Explain what can be concluded, what cannot be concluded about the last peak, and how coupling the GC instrument to a mass spectrometer strengthens identification.