16. Hydroxy compounds
A section of Chemistry, 9701
Listing 10 of 190 questions
The reducing agent LiAl H4 can be synthesised by reacting aluminiumchloride with lithiumhydride, LiH. At 200 °C, aluminiumchloride exists as Al 2Cl 6. Draw the structure of Al 2Cl 6, showing fully any coordinate (dative covalent) bonds in the molecule.  At 1000 °C, aluminiumchloride exists as Al Cl 3. State the bond angle in Al Cl 3.  ° Lithiumhydride contains the ions Li+ and H–. State the electronic configuration of these two ions. Li+ H–  LiAl H4 decomposes slowly to form LiAl and H2. LiAl H4→ LiAl + 2H2LiAl shows metallic bonding. Describe metallic bonding. LiAl H4 cannot be used in aqueous solution because it reacts with water to produce LiOH, H2and a white precipitate which is soluble in excess sodiumhydroxide. Identify the white precipitate. Two students try to prepare 2‑hydroxybutanoic acid in the laboratory. O 2-hydroxybutanoic acid OH OH Both students oxidise butane‑1,2‑diol to form P in reaction1. One student then reduces P using LiAl H4. Q is formed. The other student reduces P using NaBH4. R is formed. butane-1,2-diol OH OH P O OH O reaction 1 reaction 2 LiAl H4 reaction 3 NaBH4 Q R State the reagents and conditions required for reaction1. Only one of the students successfully prepares 2‑hydroxybutanoic acid. Identify which of Q or R is 2‑hydroxybutanoicacid and explain the difference between reactions2 and 3. A third student prepares 2‑hydroxybutanoicacid using propanal as the starting material. In step1 the student reacts propanal with a mixture of NaCN and HCN. C H C S H CN O C2H5 OH C2H5 C H COOH OH C2H5 step 1 NaCN / HCN step 2 HCl / reflux Draw the mechanism for the reaction of propanal with the mixture of NaCN and HCN to form S. ● Identify the ion that reacts with propanal. ● Draw the structure of the intermediate of the reaction. ● Include all charges, partial charges, lone pairs and curly arrows. C H C S H CN O C2H5 OH C2H5  Complete the equation for the reaction in step 2, when S is heated under reflux with HCl . C2H5CH(OH)CN + → C2H5CH(OH)COOH +  The infrared spectrum of an organic compound is shown. The organic compound is either S or 2‑hydroxybutanoicacid. transmittance % wavenumber / cm–1 Deduce the identity of the compound. Give two reasons for your answer. In your answer, identify any relevant absorptions above 1500 cm–1 in the spectrum and the bonds that correspond to these absorptions. 
9701_w20_qp_21
THEORY
2020
Paper 2, Variant 1
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The reducing agent LiAl H4 can be synthesised by reacting aluminiumchloride with lithiumhydride, LiH. At 200 °C, aluminiumchloride exists as Al 2Cl 6. Draw the structure of Al 2Cl 6, showing fully any coordinate (dative covalent) bonds in the molecule.  At 1000 °C, aluminiumchloride exists as Al Cl 3. State the bond angle in Al Cl 3.  ° Lithiumhydride contains the ions Li+ and H–. State the electronic configuration of these two ions. Li+ H–  LiAl H4 decomposes slowly to form LiAl and H2. LiAl H4→ LiAl + 2H2LiAl shows metallic bonding. Describe metallic bonding. LiAl H4 cannot be used in aqueous solution because it reacts with water to produce LiOH, H2and a white precipitate which is soluble in excess sodiumhydroxide. Identify the white precipitate. Two students try to prepare 2‑hydroxybutanoic acid in the laboratory. O 2-hydroxybutanoic acid OH OH Both students oxidise butane‑1,2‑diol to form P in reaction1. One student then reduces P using LiAl H4. Q is formed. The other student reduces P using NaBH4. R is formed. butane-1,2-diol OH OH P O OH O reaction 1 reaction 2 LiAl H4 reaction 3 NaBH4 Q R State the reagents and conditions required for reaction1. Only one of the students successfully prepares 2‑hydroxybutanoic acid. Identify which of Q or R is 2‑hydroxybutanoicacid and explain the difference between reactions2 and 3. A third student prepares 2‑hydroxybutanoicacid using propanal as the starting material. In step1 the student reacts propanal with a mixture of NaCN and HCN. C H C S H CN O C2H5 OH C2H5 C H COOH OH C2H5 step 1 NaCN / HCN step 2 HCl / reflux Draw the mechanism for the reaction of propanal with the mixture of NaCN and HCN to form S. ● Identify the ion that reacts with propanal. ● Draw the structure of the intermediate of the reaction. ● Include all charges, partial charges, lone pairs and curly arrows. C H C S H CN O C2H5 OH C2H5  Complete the equation for the reaction in step 2, when S is heated under reflux with HCl . C2H5CH(OH)CN + → C2H5CH(OH)COOH +  The infrared spectrum of an organic compound is shown. The organic compound is either S or 2‑hydroxybutanoicacid. transmittance % wavenumber / cm–1 Deduce the identity of the compound. Give two reasons for your answer. In your answer, identify any relevant absorptions above 1500 cm–1 in the spectrum and the bonds that correspond to these absorptions. 
9701_w20_qp_23
THEORY
2020
Paper 2, Variant 3
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Lactones are cyclic esters. Under suitable conditions, lactones form from molecules that have both an alcohol and a carboxylic acid functional group. Equation1 shows an example of the formation of a lactone. equation 1 + H2O OH OH O O a lactone O Fig.5.1 shows the synthesis of lactoneP from compoundM. O OH HO M N P hot concentrated acidified KMnO4reaction 1 NaBH4 5-hydroxyhexanoic acid reaction 2 reaction 3 M reacts with hot concentrated acidified KMnO4to form N, C6H10O3, in reaction1. Draw the structure of N.  N is reduced by NaBH4 to form 5-hydroxyhexanoic acid in reaction2. Construct an equation for reaction2 using molecular formulae. In the equation, use to represent one atom of hydrogen from the reducing agent. Reaction2 is a nucleophilic addition. Suggest why reaction2 creates a mixture of two organic compounds. Draw lactoneP, the product of reaction3.  A student monitors the progress of reaction2 using infrared spectroscopy. Use Table5.1 to suggest why it is difficult to distinguish between N and 5‑hydroxyhexanoic acid using infrared spectroscopy. Table 5.1 bond functional group 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 2850–3100 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650 Unknown lactoneQ is analysed using mass spectrometry. Table5.2 shows information from the mass spectrum. Table 5.2 peak m/e abundance M+ 95.5 M+1 3.15 Use these data to deduce the structure of Q. Show your working. Q  
9701_w22_qp_21
THEORY
2022
Paper 2, Variant 1
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Lactones are cyclic esters. Under suitable conditions, lactones form from molecules that have both an alcohol and a carboxylic acid functional group. Equation1 shows an example of the formation of a lactone. equation 1 + H2O OH OH O O a lactone O Fig.5.1 shows the synthesis of lactoneP from compoundM. O OH HO M N P hot concentrated acidified KMnO4reaction 1 NaBH4 5-hydroxyhexanoic acid reaction 2 reaction 3 M reacts with hot concentrated acidified KMnO4to form N, C6H10O3, in reaction1. Draw the structure of N.  N is reduced by NaBH4 to form 5-hydroxyhexanoic acid in reaction2. Construct an equation for reaction2 using molecular formulae. In the equation, use to represent one atom of hydrogen from the reducing agent. Reaction2 is a nucleophilic addition. Suggest why reaction2 creates a mixture of two organic compounds. Draw lactoneP, the product of reaction3.  A student monitors the progress of reaction2 using infrared spectroscopy. Use Table5.1 to suggest why it is difficult to distinguish between N and 5‑hydroxyhexanoic acid using infrared spectroscopy. Table 5.1 bond functional group 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 2850–3100 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650 Unknown lactoneQ is analysed using mass spectrometry. Table5.2 shows information from the mass spectrum. Table 5.2 peak m/e abundance M+ 95.5 M+1 3.15 Use these data to deduce the structure of Q. Show your working. Q  
9701_w22_qp_23
THEORY
2022
Paper 2, Variant 3
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Questions Discovered
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