Chapter Fifteen Aldehydes And Ketones. Chapter 15 | Slide 2 of 36 In an aldehyde, an H atom is attached to a carbonyl group Ocarbonyl group CH 3 -C-H.

Chapter FifteenChapter FifteenAldehydes

And Ketones

Chapter 15 | Slide 2 of 36

In an aldehyde, an H atom is attached to a carbonyl group O carbonyl group

CH3-C-H

In a ketone, two carbon groups are attached to a carbonyl group

O carbonyl group CH3-C-CH3

Aldehydes and Ketones



Ketones as Hormones


← Fig. 15.1 Aldehydes and ketones are related to alcohols in the same manner that alkenes are related to alkanes.

Aldehydes and Ketones cont’d



→ Fig. 15.3 Aldehydes and ketones with the same number of carbon atoms and the same degree of saturation are structural isomers.


Naming Aldehydes

• Aldehydes are named by replacing the “e” with “____.”• The parent chain must contain the –_______ group.• The –CHO carbon is always carbon ___.• When attached to a ring “carbaldehyde” is used.

O

propan e al

O

hexen e al

2,5-dimethyl

4-ethyl 1

2 3

4 5 6

O

cyclopentane-carbaldehyde

2-


← Fig. 15.2 Benzaldehyde, the simplest aromatic aldehyde.

.



Naming Ketones

• Ketones are named by replacing the “e” with “_____.”• The parent chain must contain the ______.• Numbering begins nearer the ______.

O

butan e one

O

heptan e one

3,6-dimethyl

5-ethyl 1 2 3 4 5 6

2-2-

7


Name these aldehydes/ketones.

3-penten-2-one5-methyl-3-cyclohexenone

2-phenylpropanal cyclohexanone

O

O

O

O



© Harvey Lloyd/Peter Arnold, Inc.

←C.C 15.1←Wood Smoke contains formaldehyde and causes eyes to tear.

←Formaldehyde is a lachrymator (eye irritant)


← Fig. 15.4 Formalin is used to preserve biological specimens.


© 2005 Norbert Wu / www.norbertwu.com


© Steven Needham / Envision


→ Fig. 15.5 The delightful odor of melted butter is largely due to butanedione.





Why are some aldehydes and ketones soluble in water?


Physical Properties of Aldehydes and Ketones

• The polarity of the carbonyl group in aldehydes and ketones, which is responsible for many of their physical properties.– They have boiling points _______ than alcohols but

_______ than alkanes.• Why?

– Nonpolar < Polar (Dipole-dipole) <H-bonds

– _____ molecular weight aldehydes and ketones are __________ in water

• Why not ________ molecular weight aldehydes and ketones?

– Most aldehydes and ketones have odors




• Oxidation of alcohols. – Primary alcohols

yield aldehydes.– Secondary alcohols

yield ketones.O

O

From primaryalcohols

From secondaryalcohols

Synthesis of Aldehydes and Ketones


R

OH

PCCCH2Cl2

• Oxidation reactions:

R

OH

Na2Cr2O7, H2O, CH3CO2H

R

PCC = Pyridinium chlorochromate


• Ketones are unreactive to oxidation because no hydrogens are on the carbon.

R

O

AgNO3NH4OH

H R

O

OH

No ReactionR

O

R'

AgNO3NH4OH

Oxidation of Aldehydes


Reduction of Aldehydes and Ketones

• Reduction: Adding hydrogen across the carbonyl– Aldehyde primary alcohol– Ketone secondary alcohol

+ H2

+ H2

CH3

CH O

CH3

CH2 OH

CH3

CCH3

O

CH3

CHCH3

OH


Addition Reactions

• Polar molecules can add to the carbonyl in aldehydes and ketones

• The negative part of the added molecule adds to the positive carbonyl carbon

• The positive part of the added molecule adds to the negative carbonyl oxygen

• + - + -

• -C=O + X-Y -C-O-X Y


Acetal Formation

• Alcohols add to the carbonyl of aldehydes and ketones

• The addition of two alcohols forms an acetal.

• O O-CH3

• CH3-C-H + 2 CH3-OH CH3-C-H + H2O

• O-CH3

Hydrolysis of acetals yield the aldehyde or ketone and the alcohols that originally formed the acetal


Hemiacetal Formation

• The addition of one alcohol to an aldehyde or ketone forms an intermediate called a hemiacetal

• Usually, hemiacetals are unstable and hard to isolate.

• O O-CH3

• CH3-C-H + 2 CH3-OH CH3-C-H + H2O

• O-H



CC 15.3 Diabetes, aldehyde oxidation, and glucose testing


Tests for Distinguishing between Aldehydes and Ketones

• Tollens’ test (AKA Silver Mirror test)– Tollens’ reagent, which contains Ag+, reacts with

aldehydes, but not with ketones– The aldehyde is oxidized and Ag+ is reduced to Ag,

which appears as a silver “mirror” in the test tube (or reaction vessel)



(c) The inside of the beaker becomes coated with metallic silver.

(b) The solution darkens as ethanal is oxidized to ethanoic acid.

Figs. 15.8 a-c

(a) An aqueous solution of ethanal is added to a solution of silver nitrate.


Tests for Distinguishing between Aldehydes and Ketones

• Benedict’s Test– Benedict’s reagent, which contains Cu+2, reacts with

aldehydes that have an adjacent OH group

– The aldehyde is oxidized and Cu+2 is reduced Cu2O, which appears as a brick red solid in the test tube

– Ketones do not react.



→ Fig. 15.9 Benedict’s solution turns brick red when an aldehyde reacts with it.



Work on the following learning checks as homework.


Classify each as an aldehyde (1), ketone (2) or neither(3).

O

A. CH3CH2CCH3 B. CH3-O-CH3

CH3 O

C. CH3-C-CH2CH D.

CH3

Learning Check


Name the following

O

A. CH3CH2CCH3 B.

CH3 O

C. CH3-C-CH2CH

CH3

O

Learning Check


Draw the structural formulas for each:

A. 3-Methylpentanal

B. 2,3-Dichloropropanal

C. 3-Methyl-2-butanone

Learning Check


Learning Check

• Select the compound that would have the higher boiling point– A. CH3-CH2-CH3 or CH3-CH2-OH

– B. CH3-CH2-OH or CH3-O-CH3

– C. OR O


Learning Check

• Are the following compounds soluble in water?– A. CH3-CH2-CH3

– B. CH3-CH2-OH

– C.

– D.

O

O

Chapter Fifteen Aldehydes And Ketones. Chapter 15 | Slide 2 of 36 In an aldehyde, an H atom is attached to a carbonyl group Ocarbonyl group CH 3 -C-H.

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