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. 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.
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
5. For the products above give a test that would confirm the functional group Add Brady’s reagent (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
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 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
Elimination, by Base
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:
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:
(Loss of H)
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...
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