Alcohols, Halogenoalkanes
Chapters 2.8-2.10: alcohols, halogenoalkanes, mechanisms and spectra
Consolidation questions 1. Give the names of the two primary alcohols with the molecular formula C4H10O. butan-1-ol 2-methyl propan-1-ol
2. Write the equation, using state symbols, for the reaction of ethanol with sodium.
CH3CH2OH(l) + Na(s) CH3CH2O-Na+(alc) + ½ H2(g)
3. Name the organic product above.
Sodium ethoxide
4. Give the names and structural formulae for the two possible products of the reaction of methanol with sodium dichromate(VI).
HCHO methanal HCOOH methanoic acid
(Partial oxidation) (Full oxidation)
5. For the products above give a test that would confirm the functional group
Add Brady’s reagent …show more content…
(2,4,6 dinitrophenyl hydrazine). Methanal gives bright yellow precipitate, methanoic acid dies not. To confirm the acid functional group, add sodium carbonate solution: effervescence results. 6.
Draw structural formulae for the four isomers with molecular formula C4H9Br.
A CH3CH2CH2CH2Br 1-bromopropane
B CH3CH2CHBrCH3 2-bromopropane
C CH3CHBr(CH3)CH3 2-bromo-2-methylpropane
D CH3CH(CH3)CH2Br 1-bromo-2-methylpropane
7. Which of the halogenoalkanes in the previous question will react fastest with aqueous silver nitrate? Give a reason for your answer.
C, as it forms a tertiary carbocation, which is the most stable intermediate.
8. An unknown halogenoalkane , with molecular formula C2H5X reacts with hot aqueous silver nitrate to give a yellow ppt. a) identify the halogen
Yellow ppt is AgI, so the halogen is …show more content…
iodine
b) give the formula of the organic product of the reaction
CH3CH2OH, C2H5OH or C2H6O
c) state the type of organic reaction and the mechanism occurring
Substitution, Nucleophilic
9. When 2-bromobutane reacts with hot ethanolic potassium hydroxide three products form. a) Give the names of these products
Butan-2-ol Substitution, Nucleophilic
But-1-ene Elimination, by Base
But-2-ene Elimination, by Base (2 isomers: E and Z)
b) State the type and mechanism of the reaction occurring in their formation
See above
10. Explain how IR spectroscopy can be used to distinguish between ethanol, ethanal and ethanoic acid.
Ethanal can be distinguished from the other 2 as it lacks an OH vibration. The C=O vibrations in ethanal and ethanoic acid will occur at different frequencies because in ethanal the C is bonded to methyl and H, and in ethanoic acid to methyl and OH. Similarly the OH vibrations in ethanol and ethanoic acid will occur at different frequencies. Ethanoic acid will have both C=O and OH vibrations.
11. Explain how you would distinguish 1-bromobutane from 2-bromobutane using their mass spectra.
Structural formulae:
1-bromobutane CH3CH2CH2CH2Br
2-bromobutane CH3CH2CHBrCH3
Many of the fragment ions produced by C-C bond breaking will be the same for both isomers.
However, you can only get the fragment ion CH2Br+ from 1-bromobutane and not from 2-bromobutane.
(Note that since bromine exists as two isotopes, with m/z = 79 and m/z = 81, with approximately equal abundances, this fragment ion will appear as two peaks of same height at m/z = 93 and m/z = 95.)
Similarly, you can only get C3H7+ from 1-bromobutane, and not from 2-bromobutane. Peak for this ion at m/z = 43.
12. Suggest a likely ion fragment for ethanol, and at what m/z value this would occur.
Parent ion at m/z = 46
Principal fragments and their m/e values:
CH3CH2O+ 45 (Loss of H)
CH2OH+ 31 (Breaking C-C)
CH3CH2+ 29 (Breaking C-O)
OH+ 17 (Breaking C-O)
CH3+ 15 (Breaking C-C)
13. The mass spectrum for propanal includes peaks at m/z values 29,57 and 58 a. Explain why the mass spectrum shows peaks at these values
Propanal has structural formula CH3CH2CHO, which corresponds to relative formula mass of 58.
Peak at 58 is the molecular ion CH3CH2CHO+.
Peak at 57 is the molecular ion less one hydrogen: C3H5O+ (the H may be lost from any carbon: you do not need to be able to predict which one will lose it)
Peak at 29 could be CH3-CH2+ OR else CHO+.
(These two could be distinguished by very accurate and precise high resolution mass spectrometry, which is routinely achievable on modern magnetic sector instruments. In this case, the precise masses of the C, H and O in each fragment are added up and the masses compared with experimental mass. This works because mass of O is not exactly 16 mass units etc.)
b. Suggest how the mass spectrum for propanone would differ
Both are C3H6O, so have same molecular ion peak at m/e = 58.
Propanone will have fragment ion peak at m/e = 48 (CH3CO+), which is absent from propanal mass spectrum.
14. Which of the following are green house gases? chlorine, chloromethane, nitrogen dioxide, argon, ammonia
The 3 which are underlined can absorb infrared radiation as their vibrations give rise to oscillating dipoles.
15. Classify the following reactions: a) CH3CH 3 + Br2 → CH3CH2Br + HBr Free radical substitution b) CH2=CH2 + Br2 → CH2BrCH2Br Electrophilic
addition c) CH3CH2Br + H2O →CH3CH2OH + HBr Nucleophilic substitution d) CH3CH2Br →CH2=CH2 + HBr Base elimination
16. Classify the type of attacking agent in a)b)c) a) Free radical b) Electrophile c) Nucleophile
Examination questions 1 Which of these is a tertiary alcohol? a) 2-methyl propan – 2-ol This one: C with OH group is bonded to 3 other carbon atoms b) Propan -2-ol c) Pentan -3-ol d) 2-methylpropan-1-ol (1)
2 This question is about propan -1-ol, some of whose reactions are shown below:
Reaction1 Reaction 2 Reaction 3
CH3CH2CH2ONa ← CH3CH2CH2OH → CH3CH2CHO → CH3CH2COOH A propan-1-ol B C a) i) Name the reactant which must be added to propan-1-ol to bring about Reaction 1. (1) Sodium ii) State the appearance of A , the product of Reaction 1 (2) White solid scum floating on top of liquid b) The same reagents can be used in Reaction 2 and Reaction 3, but under different conditions i) What is the name for this type of reaction? (1) Oxidation ii) Give the names of the two reagents suitable for both reactions (2) Acidified potassium dichromate (VI) Acidified sodium dichromate (VI) iii) What conditions could bring about Reaction 2? (2) Gentle warming of alcohol with acidified sodium dichromate (VI) solution. Direct, immediate distillation of product without refluxing. iv) What conditions would be used to bring about Reaction 3 (2) Reflux alcohol with excess acidified sodium dichromate (VI) solution. c) Name products B and C (2) B is propanal C is propanoic acid d) Propanol-1-ol, B and C can be distinguished using their infrared spectra. State where the distinguishing absorption s would occur and indicate the bonds responsible for them in each compound (3) Propan-1-ol and Propanoic acid will have OH vibrations at different frequencies because of different groups bonded to the OH. Propanal will have no OH vibration. Propanal and propanoic acid will have C=O vibrations, at different frequencies, but propan-1-ol will not have any C=O vibration. Propan-1-ol and propanoic acid will have C-O vibrations at different frequencies, but propanal will not. The acid will have both C=O and OH vibrations. 3 This question is about the hydrolysis of halogenoalkanes. * 2 cm3 of ethanol is added to each of three test tubes. * Three drops of 1-chlorobutane are added to the first, three drops of 1-bromobutane are added to the second , and three drops of 1-iodobutane are added to the third test tube. * A 2cm3 portion of hot, aqueous silver nitrate is added to each test tube. * A ppt forms immediately in the third test tube, slowly in the second test tube and extremely slowly in the first test tube. * In each reaction the ppt is formed by silver ions, Ag + reacting with the halide ions formed by hydrolysis of halogenoalkanes. a) i) Why was ethanol added to each test tube? (1) Solvent for halogenoalkane and silver nitrate ii) The same organic product forms in this reaction, name it (1) Butan-1-ol iii) Complete the equation for the hydrolysis of 1-bromobutane C4H9Br + H2O → C4H9OH + HBr (1) v) Name the ppt that forms v slowly in the first test tube and write an ionic equation including state symbols for its formation (3) The ppt is silver chloride. Ag+(aq) + Cl-(aq) → AgCl(s) vi) what is the colour of the ppt in the third test tube (1) Yellow vii) ammonia is added to the precipitate formed in the first test tube, describe and explain what you would observe (2) The precipitate dissolves to leave a colourless solution. Ag+(aq) + 2NH3(aq) → [Ag(NH3)2]+(aq) Colourless complex ion viii) explain why the rates of hydrolysis of the three halogenoalkanes are different (2) The difference in rates is due to the different strengths of the carbon halogen bond: Bond Rate Bond energy/kJ mol-1 C-Cl slow 346 C-Br 290 C-I fast 228 C-I bond breaks most easily as it has smallest bond energy b) 1-bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperatures to form but-1-ene i) Draw a fully labelled diagram to show the apparatus for carrying out this reaction in the laboratory (3) KOH in ethanol + 1-bromobutane ii) Suggest a chemical test for an alkene such as but-1-ene . State the colour change you would observe (2) Add 1 cm3 of bromine water. Bromine water decolourises if double bond present.
Consolidation questions 1. Give the names of the two primary alcohols with the molecular formula C4H10O. butan-1-ol 2-methyl propan-1-ol
2. Write the equation, using state symbols, for the reaction of ethanol with sodium.
CH3CH2OH(l) + Na(s) CH3CH2O-Na+(alc) + ½ H2(g)
3. Name the organic product above.
Sodium ethoxide
4. Give the names and structural formulae for the two possible products of the reaction of methanol with sodium dichromate(VI).
HCHO methanal HCOOH methanoic acid
(Partial oxidation) (Full oxidation)
5. For the products above give a test that would confirm the functional group
Add Brady’s reagent …show more content…
(2,4,6 dinitrophenyl hydrazine). Methanal gives bright yellow precipitate, methanoic acid dies not. To confirm the acid functional group, add sodium carbonate solution: effervescence results. 6.
Draw structural formulae for the four isomers with molecular formula C4H9Br.
A CH3CH2CH2CH2Br 1-bromopropane
B CH3CH2CHBrCH3 2-bromopropane
C CH3CHBr(CH3)CH3 2-bromo-2-methylpropane
D CH3CH(CH3)CH2Br 1-bromo-2-methylpropane
7. Which of the halogenoalkanes in the previous question will react fastest with aqueous silver nitrate? Give a reason for your answer.
C, as it forms a tertiary carbocation, which is the most stable intermediate.
8. An unknown halogenoalkane , with molecular formula C2H5X reacts with hot aqueous silver nitrate to give a yellow ppt. a) identify the halogen
Yellow ppt is AgI, so the halogen is …show more content…
iodine
b) give the formula of the organic product of the reaction
CH3CH2OH, C2H5OH or C2H6O
c) state the type of organic reaction and the mechanism occurring
Substitution, Nucleophilic
9. When 2-bromobutane reacts with hot ethanolic potassium hydroxide three products form. a) Give the names of these products
Butan-2-ol Substitution, Nucleophilic
But-1-ene Elimination, by Base
But-2-ene Elimination, by Base (2 isomers: E and Z)
b) State the type and mechanism of the reaction occurring in their formation
See above
10. Explain how IR spectroscopy can be used to distinguish between ethanol, ethanal and ethanoic acid.
Ethanal can be distinguished from the other 2 as it lacks an OH vibration. The C=O vibrations in ethanal and ethanoic acid will occur at different frequencies because in ethanal the C is bonded to methyl and H, and in ethanoic acid to methyl and OH. Similarly the OH vibrations in ethanol and ethanoic acid will occur at different frequencies. Ethanoic acid will have both C=O and OH vibrations.
11. Explain how you would distinguish 1-bromobutane from 2-bromobutane using their mass spectra.
Structural formulae:
1-bromobutane CH3CH2CH2CH2Br
2-bromobutane CH3CH2CHBrCH3
Many of the fragment ions produced by C-C bond breaking will be the same for both isomers.
However, you can only get the fragment ion CH2Br+ from 1-bromobutane and not from 2-bromobutane.
(Note that since bromine exists as two isotopes, with m/z = 79 and m/z = 81, with approximately equal abundances, this fragment ion will appear as two peaks of same height at m/z = 93 and m/z = 95.)
Similarly, you can only get C3H7+ from 1-bromobutane, and not from 2-bromobutane. Peak for this ion at m/z = 43.
12. Suggest a likely ion fragment for ethanol, and at what m/z value this would occur.
Parent ion at m/z = 46
Principal fragments and their m/e values:
CH3CH2O+ 45 (Loss of H)
CH2OH+ 31 (Breaking C-C)
CH3CH2+ 29 (Breaking C-O)
OH+ 17 (Breaking C-O)
CH3+ 15 (Breaking C-C)
13. The mass spectrum for propanal includes peaks at m/z values 29,57 and 58 a. Explain why the mass spectrum shows peaks at these values
Propanal has structural formula CH3CH2CHO, which corresponds to relative formula mass of 58.
Peak at 58 is the molecular ion CH3CH2CHO+.
Peak at 57 is the molecular ion less one hydrogen: C3H5O+ (the H may be lost from any carbon: you do not need to be able to predict which one will lose it)
Peak at 29 could be CH3-CH2+ OR else CHO+.
(These two could be distinguished by very accurate and precise high resolution mass spectrometry, which is routinely achievable on modern magnetic sector instruments. In this case, the precise masses of the C, H and O in each fragment are added up and the masses compared with experimental mass. This works because mass of O is not exactly 16 mass units etc.)
b. Suggest how the mass spectrum for propanone would differ
Both are C3H6O, so have same molecular ion peak at m/e = 58.
Propanone will have fragment ion peak at m/e = 48 (CH3CO+), which is absent from propanal mass spectrum.
14. Which of the following are green house gases? chlorine, chloromethane, nitrogen dioxide, argon, ammonia
The 3 which are underlined can absorb infrared radiation as their vibrations give rise to oscillating dipoles.
15. Classify the following reactions: a) CH3CH 3 + Br2 → CH3CH2Br + HBr Free radical substitution b) CH2=CH2 + Br2 → CH2BrCH2Br Electrophilic
addition c) CH3CH2Br + H2O →CH3CH2OH + HBr Nucleophilic substitution d) CH3CH2Br →CH2=CH2 + HBr Base elimination
16. Classify the type of attacking agent in a)b)c) a) Free radical b) Electrophile c) Nucleophile
Examination questions 1 Which of these is a tertiary alcohol? a) 2-methyl propan – 2-ol This one: C with OH group is bonded to 3 other carbon atoms b) Propan -2-ol c) Pentan -3-ol d) 2-methylpropan-1-ol (1)
2 This question is about propan -1-ol, some of whose reactions are shown below:
Reaction1 Reaction 2 Reaction 3
CH3CH2CH2ONa ← CH3CH2CH2OH → CH3CH2CHO → CH3CH2COOH A propan-1-ol B C a) i) Name the reactant which must be added to propan-1-ol to bring about Reaction 1. (1) Sodium ii) State the appearance of A , the product of Reaction 1 (2) White solid scum floating on top of liquid b) The same reagents can be used in Reaction 2 and Reaction 3, but under different conditions i) What is the name for this type of reaction? (1) Oxidation ii) Give the names of the two reagents suitable for both reactions (2) Acidified potassium dichromate (VI) Acidified sodium dichromate (VI) iii) What conditions could bring about Reaction 2? (2) Gentle warming of alcohol with acidified sodium dichromate (VI) solution. Direct, immediate distillation of product without refluxing. iv) What conditions would be used to bring about Reaction 3 (2) Reflux alcohol with excess acidified sodium dichromate (VI) solution. c) Name products B and C (2) B is propanal C is propanoic acid d) Propanol-1-ol, B and C can be distinguished using their infrared spectra. State where the distinguishing absorption s would occur and indicate the bonds responsible for them in each compound (3) Propan-1-ol and Propanoic acid will have OH vibrations at different frequencies because of different groups bonded to the OH. Propanal will have no OH vibration. Propanal and propanoic acid will have C=O vibrations, at different frequencies, but propan-1-ol will not have any C=O vibration. Propan-1-ol and propanoic acid will have C-O vibrations at different frequencies, but propanal will not. The acid will have both C=O and OH vibrations. 3 This question is about the hydrolysis of halogenoalkanes. * 2 cm3 of ethanol is added to each of three test tubes. * Three drops of 1-chlorobutane are added to the first, three drops of 1-bromobutane are added to the second , and three drops of 1-iodobutane are added to the third test tube. * A 2cm3 portion of hot, aqueous silver nitrate is added to each test tube. * A ppt forms immediately in the third test tube, slowly in the second test tube and extremely slowly in the first test tube. * In each reaction the ppt is formed by silver ions, Ag + reacting with the halide ions formed by hydrolysis of halogenoalkanes. a) i) Why was ethanol added to each test tube? (1) Solvent for halogenoalkane and silver nitrate ii) The same organic product forms in this reaction, name it (1) Butan-1-ol iii) Complete the equation for the hydrolysis of 1-bromobutane C4H9Br + H2O → C4H9OH + HBr (1) v) Name the ppt that forms v slowly in the first test tube and write an ionic equation including state symbols for its formation (3) The ppt is silver chloride. Ag+(aq) + Cl-(aq) → AgCl(s) vi) what is the colour of the ppt in the third test tube (1) Yellow vii) ammonia is added to the precipitate formed in the first test tube, describe and explain what you would observe (2) The precipitate dissolves to leave a colourless solution. Ag+(aq) + 2NH3(aq) → [Ag(NH3)2]+(aq) Colourless complex ion viii) explain why the rates of hydrolysis of the three halogenoalkanes are different (2) The difference in rates is due to the different strengths of the carbon halogen bond: Bond Rate Bond energy/kJ mol-1 C-Cl slow 346 C-Br 290 C-I fast 228 C-I bond breaks most easily as it has smallest bond energy b) 1-bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperatures to form but-1-ene i) Draw a fully labelled diagram to show the apparatus for carrying out this reaction in the laboratory (3) KOH in ethanol + 1-bromobutane ii) Suggest a chemical test for an alkene such as but-1-ene . State the colour change you would observe (2) Add 1 cm3 of bromine water. Bromine water decolourises if double bond present.