CHAPTER 23 ALDEHYDES AND KETONES SOLUTIONS TO REVIEW QUESTIONS. aldehyde ketone a dialdehyde. a hemiacetal a hemiketal an acetal

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1 EINS v2.qxd 12/9/07 10:48 PM Page 355 APTER 23 ALDEYDES AND KETNES SLUTINS T REVIEW QUESTINS 1. (a) R R (2 ) n aldehyde ketone a dialdehyde R (d) R R (e) R R (f) R R R a hemiacetal a hemiketal an acetal R (g) R R (h) R N and R N R R a ketal a cyanohydrin 2. Aldehydes and ketones are unable to form hydrogen bonds to themselves because they lack a hydroxy group on the carbonyl atom. This results in a lower boiling point than alcohols of similar molar mass. 3. Propanal propanone Each has the molecular formula of 3 6, so aldehydes and ketones appear to be isomeric with each other. Butanal butanone Each has the molecular formula 4 8, so the generalization seems to check out. The general formula for aldehydes and ketones is n 2n. 4. The strength of collagen depends on aldol condensations. After collagen is formed, aldehydes add along its length. ollagen fibers adjacent to each other undergo an aldol condensation. The cross linking bonds between collagen strands form a strong network, giving collagen its strength

2 EINS v2.qxd 12/9/07 10:48 PM Page hapter The carbonyl group in high molar-mass aldehydes and ketones becomes a less significant part of the molecule and the compound behaves like a hydrocarbon. onsequently, they are not very soluble in water. 6. The electrons of the carbon atom in the carbonyl group are sp 2 hybridized. Therefore the double bond consists of a sigma and a pi bond. 7. (a) When an aldehyde reacts with Benedict solution, the blue color of copper ion disappears and a red-brown precipitate (u 2 ) forms. When an aldehyde reacts with Tollens solution, the silver ion in solution forms a thin silver metal mirror on the inside of the glass container used inn the test. 8. The phenol-formaldehyde polymer is rigid because covalent bonds not only form the polymers but also cross-link the polymers to each other. 9. Formaldehyde is expensive, mixes well with wood, and is a very good adhesive. 10. MEK is an abbreviation for methyl ethyl ketone. Its main use is as a solvent, especially for lacquers and paints. 11. A ketone group,, cannot be located at the end of a carbon-carbon chain. onsequently its only possible location in both propanone and butanone is on -2 of these ketones. Therefore its location need not be numbered

3 EINS v2.qxd 12/9/07 10:48 PM Page hapter 23 - APTER 23 SLUTINS T EXERISES 1. Names of aldehydes. (a) 2 methanal, formaldehyde methylbutanal (d) 2 2 butanedial 3-phenylpropenal (e) 3 cis-2-butenal 2. Names of aldehydes (a) 3 ethanal, acetaldehyde butanal, butyraldehyde benzaldehyde (d) l 2-chloro-5-isopropylbenzaldehyde

4 EINS v2.qxd 12/9/07 10:48 PM Page hapter 23 - (e) hydroxybutanal 3. Names of ketones (a) propanone, acetone, dimethyl ketone 1-phenyl-l-propanone, ethyl phenyl ketone cyclopentanone (d) 4-hydroxy-4-methyl-2-pentanone 4. Names of ketones (a) butanone, methyl ethyl ketone (MEK) 3,3-dimethylbutanone, t-butyl methyl ketone 2,5-hexanedione (d) 1-phenyl-2-propanone, benzyl methyl ketone 5. Structural formulas (a) l 2 2 l 1,3-dichloropropanone butenal 4-phenyl-3-hexanone (d) (e) hexanal 3-ethyl-2-pentanone

5 EINS v2.qxd 12/9/07 10:48 PM Page hapter Structural formulas (a) hydroxypropanal methyl-3-hexanone 3 cyclohexanone (d) ,4,6-trichloroheptanal l l l (e) pentenal 7. Structures and correct names (a) pentanal ,5,5-trimethyl-3-hexanone 3-heptanone 8. Structures and correct names (a) ,6-dichloro-2-heptanone

6 EINS v2.qxd 12/9/07 10:48 PM Page hapter ethylpentanal hexanal 9. igher boiling point. (a) 2,5-hexanedione 2-pentanol hexanal (d) butanone 10. igher boiling point. (a) pentanal 2-hexanone benzyl alcohol (d) 1-butanol 11. igher aqueous solubility. (a) 2,5-hexanedione ethanal propanal 12. igher aqueous solubility. (a) acetaldehyde propanal 2,4-pentanediol 13. Equations for the oxidation of: (a) 3-pentanol K 2 r : 2 S 4 same product for air ( 2 ) oxidation

7 EINS v2.qxd 12/9/07 10:48 PM Page hapter 23-3-methyl-l-hexanol u " K 2 r : 2 S Equations for the oxidation of: (a) 1-propanol K 2 r : 2 S K 2 r : 2 S or u " Ag " No reaction (3 alcohol) with either oxidizing agent 15. (a)

8 EINS v2.qxd 12/9/07 10:48 PM Page hapter (a) (a) propanal, 3 2 butanone, butanal, (a) formaldehyde (methanal) propanal, propanal, (a) An aldehyde group,, must be present to give a positive Tollens test. The visible evidence for a positive Tollens test is the formation of a silver mirror on the inner walls of a test tube

9 EINS v2.qxd 12/9/07 10:48 PM Page hapter Ag + N 3 99: N Ag(s) (silver mirror) 20. (a) An aldehyde group,, must be present to give a positive Fehling test. The visible evidence for a positive Fehling test is the formation of brick red u 2 0, which precipitates during the reaction u 2+ Na 999: 2 3 Na + u 2 (s) (brick-red) 21. Product(s) when each of the following is reacted with Tollens reagent: (a) butanal butanoic acid + Ag(s) benzaldehyde benzoic acid + Ag(s) methyl ethyl ketone no reaction 22. Product(s) when each of the following is reacted with Fehling reagent: (a) propanal propanoic acid + u 2 (s) acetone no reaction 3-methylpentanal 3-methylpentanoic acid + u 2 (s) 23. (a) cyclohexanone, 3,4-dimethyl-2-pentanone, methylbutanal

10 EINS v2.qxd 12/9/07 10:48 PM Page hapter (a) 3-methylbutanal, cyclopentanone, 2 3 2,2-dimethylpropanal 25. Aldol condensation (a) butanal dilute " Na dilute NA 2 phenylethanal 26. Aldol condensation 2 3 (a) pentanone dilute Na " dilute propanal " Na

11 EINS v2.qxd 12/9/07 10:48 PM Page hapter The completed equations are: (a) dryl ERF 3 + ERF The completed equations are: (a) ( 3 ) 2 999: dryl ERF ± ( 3 ) Sequence of reactions: 2 999: (a) N 3 N 3 3 N

12 EINS v2.qxd 12/9/07 10:48 PM Page hapter dryl " Sequence of reactions: (a) ± N N N ± 2 ± K 2 r S : ethanal

13 EINS v2.qxd 12/9/07 10:48 PM Page hapter Four aldol condensation products from a mixture of ethanal (E) and propanal (P) are possible. EE PP EP PE 3 EE is PP is 3 2 EP is 3 PE is The secondary alcohol in compound I is oxidized to the ketone (compound II) (a) 3 2 and 3. The Tollens test (silver mirror) or Fehling test (red u 2 ) will give positive results with propanal but not with acetone. 3 2 and 2 Bromine will decolorize immediately with the second compound (propenal) but not with propanal. 2 2 and 3 xidize both compounds: 2-phenylethanol will give 2-phenylethanal and 1-phenylethanol will give methyl phenyl ketone. 1-phenylethanal will give a positive Tollens or Benedict test and methyl phenyl ketone will not give a positive test N 3 N 2 999: + 3 lactic acid

14 EINS v2.qxd 12/9/07 10:48 PM Page hapter N + ± N benzaldehyde 38. Pyruvic acid is changed to lactic acid by a reduction reaction. 39. The alcohols which should be oxidized to give these ketones. (a) 3-pentanone: 3-pentanol methyl ethyl ketone: 2-butanol phenyl-2-butanone: 4-phenyl-2-butanol Isomeric aldehydes and ketones of formula Aldehydes

15 EINS v2.qxd 12/9/07 10:48 PM Page hapter 23 - Ketones Benzaldehyde isomers of formula dil. " Na 3 2 dehydrate " 3 ethanal

16 EINS v2.qxd 12/9/07 10:48 PM Page hapter 23 - Pt 3 99: butanol + 3 dil. " Na 2 2 LiAl 4 99: ,3-propanediol a b n 44. In phenol, three positions, ortho, ortho, and para to the group are used in the reaction to form a thermosetting polymer. owever, in p-cresol the para position is occupied by a methyl group and cannot react with formaldehyde. This leaves the p-cresol molecule as a bifunctional monomer, resulting in a linear, thermoplastic polymer. 45. (a) 2 2,3-dihydroxypropanal 2 2 1,3-dihydroxypropanone 2 2 and

Alcohols. Copyright 2009 by Pearson Education, Inc. Copyright 2009 Pearson Education, Inc. CH 3 CH 2 CH 2 OH 1-propanol OH

Alcohols. Copyright 2009 by Pearson Education, Inc. Copyright 2009 Pearson Education, Inc. CH 3 CH 2 CH 2 OH 1-propanol OH Chapter 12 rganic Compounds with xygen and Sulfur 12.1 Alcohols, Thiols, and Ethers Alcohols An alcohol contains a hydroxyl group ( ) attached to a carbon chain. A phenol contains a hydroxyl group ( )