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Organic Chemistry Aldehydes and Ketones

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1 Organic Chemistry Aldehydes and Ketones
Chapter 17

2 Aldehydes and Ketones Carbonyl Group C=O Aldehydes Ketones
Present in aldehydes and ketones Aldehydes Ketones

3 Aldehydes Aldehydes Aldehydes Sometimes abbreviated RCHO
Contain at least one H connected to the C Aldehydes

4 Ketones Ketones Ketones Carbonyl C is connected to two alkyl groups
RCOR’ Ketones

5 Nomenclature IUPAC Suffix is “-al” for the aldehydes
Suffix is “-one” for the ketones # indicates position of ketone

6 Nomenclature NOTE: Ketone, Not keytone From Yahoo Images

7 Nomenclature An Aldehyde or Ketone takes precedence over any previously considered group

8 Nomenclature Common names - aldehydes

9 Nomenclature Common names - ketones Some are always used
- Others name each R group and end with “ketone”

10 Physical Properties Carbonyls: Cannot form H bonding with each other:
There is NOT an H connected to a F, N, O Aldehydes and Ketones are POLAR molecules and form dipole interactions Gives higher boiling and melting points

11 Physical Properties Aldehydes and Ketones can form H bonds with water!
solubility in water is about the same as alcohols yes!

12 Physical Properties Strong odors Ketones generally have pleasant odors
perfumes, flavoring agents Aldehydes odors vary some pleasant cinnaminaldehyde, vanillin some not pleasant formaldehyde Many are found in natural products

13 How do you make Aldehydes?
Aldehydes from Oxidation of 1o alcohols Problem is over oxidation to ACID! Practice a couple …………..

14 How do you make Ketones? Ketones from Oxidation of 2o alcohols
Practice a couple …………..

15 Oxidation of Aldehydes
Aldehydes are easily oxidized KMnO4 K2Cr2O7 even air oxidation carboxylic acid!

16 Oxidation of Ketones Ketones resist oxidation:
under mild or normal conditions, no reaction more severe conditions yield mixtures CO2 and H2O under extreme conditions [O] This difference in reactivity can be used to Tell the difference between an aldehyde and ketone


18 Reaction 1. Oxidation – Tollens Test - Benedicts Test
2. Reduction – Hydrogen addition – NaBH4 reagent 3. Addition of Alcohols – hemiacetal/acetal and tautomerism

19 Tollen’s Test The Silver Mirror Test Ag(NH3)2+ + aldehyde
Oxidation of Aldehydes Ag+ ion in aq. ammonia NO reaction with KETONES Ag(NH3) aldehyde Silver Mirror Ag NH Ag(NH3)2+ Ag(NH3)2+ + RCHO Ago + RCOO- + 4NH3

20 Benedict’s Test Cu++ + aldehyde Cu+(oxide) + acid
Oxidation of Aldehydes Cu++ ion, aqueous Orange to red ppt. NO reaction with KETONES Cu2+ Cu+ Cu aldehyde Cu+(oxide) acid

21 Benedict’s Test Oxidation of Aldehydes overall reaction Cu2O

22 Chemical Properties - Addition to C=O
Other reactions are ADDITION Reactions Bond is polar + and - Negatives are attracted to C Positives are attracted to O - + B

23 Addition of H2 Reduction to Alcohols
Hydrogen gas and a catalyst (Ni, Pd, Pt) Similar to alkene to alkane reduction B

24 Addition of H2 Reduction to Alcohols
Will reduce ketones to 2o alcohols Slower reaction than reduction of C=C C=C is reduced faster (first) if both C=O and C=C B

25 Addition of H2 using NaBH4
Reduction to Alcohols NaBH4 does not allow the reaction of the carbon carbon double bond B

26 Addition of Alcohol In the addition of R-OH to form an “acetal” the First step is the formation of a “hemiacetal” This is when an -OH and -OR are both on same C B

27 Formation of Acetals IF strong acid (HCl) is present, a second alcohol reacts to form the acetal (two -OR groups on C) + H2O B

28 Addition of Alcohol - Acetals
Step 1 Step 2 + H2O B

29 Formation of Acetals ? Addition of R-OH
acid catalyzed, 2 moles of alcohol react ? B

30 Formation of Acetals Addition of R-OH
acid catalyzed, 2 moles of alcohol react Draw the Hemi B

31 Formation of Acetals Acetal reaction in equilibrium B

32 Formation of Acetals Acetal reactions ? B

33 Formation of Acetals Acetal reactions ? 1o alcohol B

34 Formation of Acetals Hemiacetal reactions (formation of hemiacetals)
likely when within the same molecule CH 2 O OH or H a cyclic hemiacetal 1 3 4 5 1o alcohol B

35 Formation of Acetals Cyclic hemiacetals
Reacts with a 2nd. molecule of alcohol Results in a cyclic acetal 1o alcohol B

36 Formation of Acetals Which are hemiacetals / acetals? 1 2 3 4 5 6 7 8
9 10 B

37 Keto-Enol Tautomerism
Equilibrium that exists Keto (carbonyl) to Enol (alkene/alcohol) B

38 Keto-Enol Tautomerism
Equilibrium called Tautomerism Keto form (more stable) (less stable) 1o alcohol B

39 Keto-Enol Tautomerism
Equilibrium called Tautomerism Most enols are less stable 1o alcohol B

40 Important Compounds Formaldehyde Gas at RT Soluble in H2O Formalin
found in labs preserves by denaturing proteins Used to produce polymers B

41 Important Compounds Acetaldehyde bp 21o C Converted to trimer
3 units of acetaldehyde called paraldehyde once used as a hypnotic/sleep-producer B

42 Important Compounds Acetone bp 56o C Infinitely soluble in H2O
Excellent industrial solvent: paints, varnishes, resins coatings, nail polish Produced in the body diabetic ketoacidosis “acetone breath” B

43 Important Compounds -chloroacetophenone lachrymators
tearing of eyes, etc. Used as a tear gas Active ingredient in “Mace” B

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