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Organic Chemistry Aldehydes and Ketones. Chapter 17. Aldehydes and Ketones. Carbonyl Group C=O Present in aldehydes and ketones. Aldehydes. Ketones. Aldehydes. Aldehydes Sometimes abbreviated RCHO Contain at least one H connected to the C. Aldehydes. Ketones. Ketones

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Organic Chemistry Aldehydes and Ketones

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Organic chemistry aldehydes and ketones l.jpg

Organic ChemistryAldehydes and Ketones

Chapter 17


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Aldehydes and Ketones

  • Carbonyl Group C=O

    • Present in aldehydes and ketones

Aldehydes

Ketones


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Aldehydes

  • Aldehydes

    • Sometimes abbreviated RCHO

    • Contain at least one H connected to the C

Aldehydes


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Ketones

  • Ketones

    • Carbonyl C is connected to two alkyl groups

    • RCOR’

Ketones


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Nomenclature

  • IUPAC

    • Suffix is “-al” for the aldehydes

    • Suffix is “-one” for the ketones

    • # indicates position of ketone


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Nomenclature

NOTE:

Ketone,

Not keytone

From Yahoo Images


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Nomenclature

  • An Aldehyde or Ketone takes precedence over any previously considered group


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Nomenclature

  • Common names - aldehydes


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Nomenclature

  • Common names - ketones

    • Some are always used

- Others name each R group and end with “ketone”


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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


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Physical Properties

  • Aldehydes and Ketones

    • can form H bonds with water!

    • solubility in water is about the same as alcohols

yes!


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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

http://www.youtube.com/watch?v=KDohVakqkic


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How do you make Aldehydes?

  • Aldehydes from Oxidation of 1o alcohols

    • Problem is over oxidation to ACID!

Practice a couple …………..


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How do you make Ketones?

  • Ketones from Oxidation of 2o alcohols

Practice a couple …………..


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Oxidation of Aldehydes

  • Aldehydes are easily oxidized

    • KMnO4

    • K2Cr2O7

    • even air oxidation carboxylic acid!


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[O]

Oxidation of Ketones

  • Ketones resist oxidation:

    • under mild or normal conditions, no reaction

    • more severe conditions yield mixtures

    • CO2 and H2O under extreme conditions

This difference in reactivity can be used to

Tell the difference between an aldehyde and ketone


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Reaction

1.Oxidation – Tollens Test

- Benedicts Test

2.Reduction – Hydrogen addition

– NaBH4 reagent

3.Addition of Alcohols – hemiacetal/acetal

and tautomerism


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Tollen’s Test

  • The Silver Mirror Test

  • Oxidation of Aldehydes

    • Ag+ ion in aq. ammonia

    • NO reaction with KETONES

      Ag(NH3)2+ + aldehyde

Silver Mirror

Ag+ + 2 NH3 Ag(NH3)2+

Ag(NH3)2+ + RCHO Ago + RCOO- + 4NH3


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Cu+

Cu2+

Benedict’s Test

  • Oxidation of Aldehydes

    • Cu++ ion, aqueous

    • Orange to red ppt.

    • NO reaction with KETONES

Cu+++ aldehyde Cu+(oxide)+ acid


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Cu2O

Benedict’s Test

  • Oxidation of Aldehydes

    • overall reaction


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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


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Addition of H2

  • Reduction to Alcohols

    • Hydrogen gas and a catalyst (Ni, Pd, Pt)

    • Similar to alkene to alkane reduction

B


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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


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Addition of H2 using NaBH4

  • Reduction to Alcohols

    • NaBH4 does not allow the reaction of the carbon carbon double bond

B


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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


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Formation of Acetals

IF strong acid (HCl) is present, a second alcohol reacts to form the acetal (two -OR groups on C)

+ H2O

B


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Addition of Alcohol - Acetals

Step 1

Step 2

+ H2O

B


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Formation of Acetals

  • Addition of R-OH

    • acid catalyzed, 2 moles of alcohol react

?

B


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Formation of Acetals

  • Addition of R-OH

    • acid catalyzed, 2 moles of alcohol react

Draw the Hemi

B


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Formation of Acetals

  • Acetal reaction in equilibrium

B


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Formation of Acetals

  • Acetal reactions

?

B


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Formation of Acetals

  • Acetal reactions

?

1o alcohol

B


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H

O

O

OH

5

4

3

2

1

O

5

1

CH

CH

CH

CH

CH

or

2

2

2

2

2

4

OH

O

3

a cyclic hemiacetal

Formation of Acetals

  • Hemiacetal reactions (formation of hemiacetals)

    • likely when within the same molecule

1o alcohol

B


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Formation of Acetals

  • Cyclic hemiacetals

    • Reacts with a 2nd. molecule of alcohol

    • Results in a cyclic acetal

1o alcohol

B


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Formation of Acetals

  • Which are hemiacetals / acetals?

1

2

3

4

5

6

7

8

9

10

B


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Keto-Enol Tautomerism

  • Equilibrium that exists

  • Keto (carbonyl) to Enol (alkene/alcohol)

B


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Keto form

(more stable)

(less stable)

Keto-Enol Tautomerism

  • Equilibrium called Tautomerism

1o alcohol

B


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Keto-Enol Tautomerism

  • Equilibrium called Tautomerism

Most enols are

less stable

1o alcohol

B


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Important Compounds

  • Formaldehyde

    • Gas at RT

    • Soluble in H2O

    • Formalin

      • 37% formaldehyde

      • found in labs

      • preserves by denaturing proteins

    • Used to produce polymers

B


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Important Compounds

  • Acetaldehyde

    • bp 21o C

    • Converted to trimer

      • 3 units of acetaldehyde

      • called paraldehyde

      • once used as a hypnotic/sleep-producer

B


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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


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Important Compounds

  • -chloroacetophenone

    • lachrymators

      • tearing of eyes, etc.

    • Used as a tear gas

    • Active ingredient in “Mace”

B


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