15. Halogen compounds
A section of Chemistry, 9701
Listing 10 of 284 questions
Describe the difference in reactivity between chloroethane and chlorobenzene with OH–. Explain your answer. Compound T, C5H9O2Cl, is a useful synthetic intermediate. shows some reactions of T. T Z, C6H13NO2 O O Cl O O NC step 1 step 2 W X excess NaOHOH heat + Y + excess HCl heat Give the systematic name for T. Draw the structures of W, X, Y and Z in . State the reagents and conditions for steps 1 and 2 in . step 1 step 2 The proton (1H) NMR spectrum of compound T, C5H9O2Cl, in CDCl 3 is shown in . T O O chemical shift δ / ppm δ 3.9 δ 3.7 δ 2.8 δ 1.2 Cl Table 8.1 environment of proton example chemical shift range δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Suggest why CDCl 3 is used as a solvent instead of CHCl 3 for the proton (1H) NMR spectrum. Complete Table 8.2 for the proton (1H) NMR spectrum of T. Table 8.2 chemical shift δ / ppm environment of proton splitting pattern number of 1H atoms responsible for the peak 1.2 2.8 3.7 3.9 Explain the splitting pattern of the peak at δ 3.9 ppm.
9701_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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M reacts to form R by the addition of one reagent, as shown in . HO reagent M R HO Identify the reagent and conditions for this reaction. R is also made from M by two steps, as shown in . HO step 2 M R HO Br step 1 Q Br Identify the reagents and conditions for steps 1 and 2 in . step 1 step 2 Name the mechanism for step 1 in . The infrared spectrum of R is shown in . wavenumber / cm–1 transmittance / % Table 5.1 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650 Use the absorptions in the region above 1500 cm–1 in Table 5.1 when answering this question. • Add F to to identify the peak that is present in an infrared spectrum of both Q and R. Identify the bond that corresponds to the absorption for F. • Add G to to identify the peak that is not present in an infrared spectrum of Q. Identify the bond that corresponds to the absorption for G. Y is made from Q in a three-step reaction. Br Q W X Y Br KCN in ethanol / heat reducing agent Z step 2 step 3 step 1 O HO O OH HO OH Draw the structure of W in the box in . In step 2, W is heated with HCl to produce X and an inorganic product. Identify the formula of the inorganic product. In step 3, X reacts with reducing agent Z to produce Y. Complete the equation for the reaction of X with Z. Use a molecular formula to represent the organic product. Use to represent one atom of hydrogen from Z. …… C8H12O4 + …… Identify Z.
9701_s24_qp_23
THEORY
2024
Paper 2, Variant 3
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One method of making 1-bromobutane in the laboratory is described below. Stage 1 Place 35 g of powdered sodium bromide, 30 cm3 of water, and 25 cm3 (20 g) of butan-1-ol, in a 250 cm3 two necked flask fitted with a tap funnel and reflux condenser. Stage 2 Concentrated sulfuric acid (25 cm3) is then placed in the tap funnel and added drop by drop to the reagents in the flask, keeping the contents well shaken and cooled occasionally in an ice-water bath. The overall reaction may be considered to take place in two stages. In the first stage the inorganic reagents react together to form HBr. In the second stage, the organic reagent reacts with the HBr that is formed in the first stage. Write an equation for each of these stages. stage I stage II In this preparation, by using the amounts given above, one of the reagents, sodium bromide or butan-1-ol, will be present in an excess. Use your equations in and the data above to determine, by calculation, which reagent is in an excess. In a laboratory preparation of 1-bromobutane, when 15.4 g of butan-1-ol was used, 22.5 g of 1-bromobutane was obtained after purification. Calculate the yield of 1-bromobutane as a percentage of the theoretical maximum yield. When the concentrated sulfuric acid is added to the reaction mixture (stage 2), unless the temperature is controlled carefully, the acid may react with either of the original reactants (sodium bromide or butan-1-ol) to give at least two by-products, one of which is inorganic and the other organic. What inorganic and organic by-products may be formed? In each case, identify one by-product and state the role of the concentrated sulfuric acid in the formation of this by-product. inorganic by-product role of conc. H2SO4 organic by-product role of conc. H2SO4
9701_w09_qp_22
THEORY
2009
Paper 2, Variant 2
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All the carbon atoms in benzene lie in the same plane. This means that they are coplanar, but this is not the case with cyclohexane. benzene cyclohexane By rotating the molecule around its several C–C bonds, all the carbon atoms in butane can be made to lie in the same plane, but this is not the case with methylpropane. CH2 CH3 CH2 H3C CH3 H3C H3C H butane methylpropane By considering the 3-dimensional geometry of the following five molecules, and allowing rotations around C–C bonds, decide whether or not the carbon atoms in each molecule can be arranged in a coplanar fashion. Then place a tick in the appropriate column in the table below. A B C D E CH3 CH3 CH3CH(OH)CO2H CH3 H2N O O C C H3C H3C O C NO2 H C compound all carbon atoms can be coplanar not all carbon atoms can be coplanar A B C D E Methylbenzene can react with chlorine under different conditions to give the monochloro derivatives F and G. F G CH3 CH3 I II CH2Cl Cl Suggest reagents and conditions for each reaction. reaction I reaction II Benzyl benzoate is a constituent of many perfumery products, and has also been used in the treatment of the skin condition known as scabies. It can be made from methylbenzene by the following route, which uses one of the chlorination reactions from . CO2H CH2OH CH3 III IV V VI H C CH2 O O benzyl benzoate Draw the structural formula of the intermediate H in the box above. Suggest reagents and conditions for each reaction. reaction Ill reaction V reaction VI State the type of reaction occurring during reaction Ill, reaction V.
9701_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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Questions Discovered
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