13. An introduction to AS Level organic chemistry
A section of Chemistry, 9701
Listing 10 of 507 questions
An organic compound, E, has the following composition by mass: C, 48.7%; H, 8.1%; O, 43.2%. Calculate the empirical formula of E. When vaporised in a suitable apparatus, 0.130 g of E occupied a volume of 58.0 cm3 at 127 °C and 1.00 × 105 N m–2. Use the expression pV = mRT Mr to calculate Mr of E, where m is the mass of E. Hence calculate the molecular formula of E. Compound F, is an ester with the molecular formula C4H8O2. F is one of four isomers, S, T, U, and V, that are all esters. In the boxes below, the structural formula of S is given. Draw the structural formulae of the other three isomers of F that are esters. HCO2CH(CH3)2 S T U V When the ester F is hydrolysed, an alcohol G is produced. What reagent can be used to hydrolyse an ester to an alcohol? What other type of organic compound is produced at the same time? On mild oxidation, the alcohol G gives a compound H which forms a silver mirror with Tollens’ reagent. What functional group does the reaction with Tollens’ reagent show to be present in compound H? Give the name of this group. What type of alcohol is G? What could be the structural formula of the alcohol G? Which of the four isomers, S, T, U, or V, could not be F? Explain your answer.
9701_s10_qp_22
THEORY
2010
Paper 2, Variant 2
View
A mixture of amino acids may be separated using electrophoresis. A typical practical set-up is shown in the diagram. d.c. power supply + – glass slides filter paper soaked in buffer solution amino acid mixture placed here electrolyte When the power supply is switched on, some amino acids may not move, but remain stationary. Suggest an explanation for this observation. The amino acid glycine has the formula H2NCH2CO2H. Identify the species formed on the filter paper if glycine moves to the left end of the filter paper. The following result was obtained from another electrophoresis. What can be deduced about the relative sizes of, and charges on, the amino acid species A, B and C? A + – B mixture placed here C amino acid relative size charge A B C The sequence of amino acids in a polypeptide may be determined by partial hydrolysis of the chain into smaller pieces, often tripeptides. Following such a partial hydrolysis, the following tripeptides were obtained from a given polypeptide. ala-gly-asp gly-ala-gly lys-val-ser ser-ala-gly val-ser-ala Given that the N-terminal amino acid is lysine suggest the amino acid sequence of the shortest polypeptide that would give the above tripeptides. The structural formulae of the amino acids in the polypeptide are given below. abbreviation amino acid structural formula ala alanine H2NCH(CH3)CO2H asp aspartic acid H2NCH(CH2CO2H)CO2H gly glycine H2NCH2CO2H lys lysine H2NCH(CH2CH2CH2CH2NH2)CO2H ser serine H2NCH(CH2OH)CO2H val valine H2NCH(CH(CH3)2)CO2H Which of the tripeptides in has the lowest Mr? Select one amino acid from those listed in the table which contains an ionic side-chain at pH 8.
9701_s10_qp_42
THEORY
2010
Paper 4, Variant 2
View
A mixture of amino acids may be separated using electrophoresis. A typical practical set-up is shown in the diagram. d.c. power supply + – glass slides filter paper soaked in buffer solution amino acid mixture placed here electrolyte When the power supply is switched on, some amino acids may not move, but remain stationary. Suggest an explanation for this observation. The amino acid glycine has the formula H2NCH2CO2H. Identify the species formed on the filter paper if glycine moves to the left end of the filter paper. The following result was obtained from another electrophoresis. What can be deduced about the relative sizes of, and charges on, the amino acid species A, B and C? A + – B mixture placed here C amino acid relative size charge A B C The sequence of amino acids in a polypeptide may be determined by partial hydrolysis of the chain into smaller pieces, often tripeptides. Following such a partial hydrolysis, the following tripeptides were obtained from a given polypeptide. ala-gly-asp gly-ala-gly lys-val-ser ser-ala-gly val-ser-ala Given that the N-terminal amino acid is lysine suggest the amino acid sequence of the shortest polypeptide that would give the above tripeptides. The structural formulae of the amino acids in the polypeptide are given below. abbreviation amino acid structural formula ala alanine H2NCH(CH3)CO2H asp aspartic acid H2NCH(CH2CO2H)CO2H gly glycine H2NCH2CO2H lys lysine H2NCH(CH2CH2CH2CH2NH2)CO2H ser serine H2NCH(CH2OH)CO2H val valine H2NCH(CH(CH3)2)CO2H Which of the tripeptides in has the lowest Mr? Select one amino acid from those listed in the table which contains an ionic side-chain at pH 8.
9701_s10_qp_43
THEORY
2010
Paper 4, Variant 3
View
The compound trans -4-hydroxy-2-nonenal (HNE) is thought to lead to infections of the lung when cigarettes are smoked. O OH CH3(CH2)4CH(OH)CH=CHCHO trans -4-hydroxy-2-nonenal What is the empirical formula of trans -4-hydroxy-2-nonenal? HNE contains an alkene group. Name as fully as you can two other functional groups which are present in the HNE molecule. How would you confirm the presence of the alkene group in HNE? State the reagent used and the observation you would make. reagent observation HNE is a reactive compound. Give the structural formulae of all of the carbon-containing compounds formed in each case when HNE is reacted separately with the following reagents. hot concentrated manganate(ions in acid solution hot phosphorus trichloride, PCl 3 sodium tetrahydridoborate(, NaBH4
9701_s11_qp_23
THEORY
2011
Paper 2, Variant 3
View
Organic compounds which contain oxygen may contain alcohol, aldehyde, carboxylic acid, ester or ketone functional groups. The functional groups may be identifi ed by their reactions with specifi c reagents. Compound X has the empirical formula CH2O and Mr of 90. There is no reaction when X is treated with NaHCO3. What functional group does this test show to be not present in X? When 0.600 g of X is reacted with an excess of Na, 160 cm3 of H2, measured at room temperature and pressure, is produced. What functional group does this reaction show to be present in X? Use the data to calculate the amount, in moles, of hydrogen atoms produced from 0.600 g of X. Hence, show that each molecule of X contains two of the functional groups you have given in . When X is warmed with Fehling’s reagent, a brick red precipitate is formed. Treatment of X with 2,4-dinitrophenylhydrazine reagent produces an orange solid. What functional group do these reactions show to be present in X? Draw the displayed formula of this functional group. Use your answers to , and to deduce the structural formula of X. What is the structural formula of the organic product of the reaction of X with Fehling’s reagent? Compound X can be both oxidised and reduced. Give the structural formula of the compound formed when X is reacted with NaBH4 under suitable conditions. Give the structural formula of the compound formed when X is heated under refl ux with acidifi ed K2Cr2O7.
9701_s12_qp_21
THEORY
2012
Paper 2, Variant 1
View
Questions Discovered
507