1435-1436 2014-2015 Aldehydes and ketones 1. Learning Objectives Chapter eight introduces carbonyl...

1435-14362014-2015

Aldehydes and ketones

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Learning Objectives

Chapter eight introduces carbonyl compounds and reactions that involve a nucleophilic attack at the carbonyl carbon in addition to the other topics. By the end of this chapter the student will:

Know the structural differences between aldehydes and ketonesKnow how to draw aldehydes and ketones know the common and IUPAC nomenclature of aldehydes and ketones Know the physical properties of aldehydes and ketonesKnow how to synthesize an aldehyde or a ketone from a compound without

that functionality. Know the different nucleophilic attack reactions at the carbonyl carbon and

the specific products formed in each case.


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ALDEHYDES: STRUCTURE AND NOMENCLATURE General formula: RCHO or Bond line formula The polarity of C=O

The aldehyde group is always (terminal)at the end of a chain

145 Chem.

Common Nomenclature Of AldehydesCommon name of aldehydes are derived from the common name of

the correspounding acid Some aliphatic aldehydes have common names which have to be

memorized.

Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde


R-C-H

O

R O R H

O

C

O

C

O

E

Nu

3

4

Some aromatic aldehydes have common names such as:

H

O

H

OOH

H3CO

IUPAC Nomenclature Select the longest continuous carbon chain that contains the H-C=O group to get the name of the parent hydrocarbon, then replace the ending e by the suffix –al The CHO group is assigned the local 1 and takes precedence over other functional groups that may present such as C=O(ketone),–OH, C=C, CΞC, ORFor cyclic aldehydes in which the –CHO group is attached to the ring, the suffix carbaldehyde is used.

Salicylaldehyde (o-Hydroxybenzaldehyde) Anisaldehyde (p-methoxybezaldehyde)


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H

O

OH

OCl

HO

Methanal Ethanal Propanal Butanal

3-Chlorobutanal 3-Hydroxypropanal 2-Butenal

Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde.

H

OH

O

H

OH

O OH

H3COO2NBenzaldehyde 2-Hydroxybenzaldehyde 4-Nitrobenzaldehyde 4-Methoxybenzaldehyde


CHO

OHCis-2-Hydroxy cyclopentane carbaldehyde

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General formula: RCOR’ (R and R’=alkyl or aryl)

Common names of ketones derived by listing the alkyl substituents attached to the

carbonyl group in alphabetical order, followed by the word ketone.

In common names carbon atoms near the carbonyl group are often designated using

Greek letters (α, ᵝ, ɣ , δ…..) beginning with carbon next the carbonyl group.

When a complex molecules contains more than one of functional groups, an order

of precedence is used to determine the name. The functional group priority order in nomenclature system is as following:

Acid and derivatives > aldehyde > ketone > alcohol > amine > alkene > alkyne > ether

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KETONES:STRUCTUR AND NOMENCLATURE


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IUPAC Nomencalture :

Select the longest continuous carbon chain that contains the C=O

group to get the name of the parent hydrocarbon, then replace the ending

e by the suffix –one

The chain is numbered in such a way as give the lowest number to the

C=O group.

The prefix of oxo is used if there are higher ranking functional groups

present. 7


CH3 C CH3

O

CH3 C C6H5

O

CH3 C CH=CH 2

O

H5C6 C

O

C6H5Acetone Acetophenone Benzophenone Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone

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C2H5 C

O O

C2H5

CHO

O

OH

Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone

Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal


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Physical Properties OF Aldehydes And Ketones The carbonyl group is polar; with a partial negative charge on oxygen atom, and

partial positive charge on carbon atom. Because the polarity of the carbonyl group, aldehydes and ketones are polar

compounds.

1) Boiling and melting points Higher melting and boiling points compared to analogous alkanes due to they

show dipole-dipole attractions.

These attractions although important, are not as strong as interactions due to hydrogen bonding as a result, the boiling points of aldehydes and ketones are higher than those of non polar alkanes, but lower than those of alcohols whose molecules are connected together by H-bonds.

C O C O

dipole-dipole attaraction

C O

O C


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2) Solubility Lower aldehydes and ketones are are more soluble than alkanes

but less soluble than alcohols in aqueous media

C O

H

O

H CO


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Preparation Of Aldehydes And ketones:1- Oxidation of Alcohols


Cu/CH3CH2OH H3C CH

or PCC

O

CH3CH2OH H3C C-OH

O

KMnO4

Cu/CH3CHCH3 H3C C-CH3

or KMnO4

OOH

or PCC

PCC =N

, CrO3. HCl Pridinium Chloro chromate

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2- Ozonolysis of Alkenes: results in formation of aldehydes or ketones depending on structure of the alkene used.

i) O3

ii) Zn / H2O

CH3CH2CHO + CH3CHO

i) O3

ii) Zn / H2O

O

O

Diketone

two aldehydes

1] O3

2]Zn/ H2O

A

A

A

A

OA

AO

A

A+


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3- Hydration Of Alkynes

4- Friedel Crafts Acylation

N.B: -COR group is m-director and deactivating towards electrophiles

+ R

O

Cl

AlCl3 R

O

H2SO4,HgSO4C C C

H

OH

an enol unstable

C

H

H

carbonyl more stableO

H2O,

HC CHH2SO4,HgSO4H2O,

H

O

C CHH2SO4,HgSO4H2O,

O

H3C


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Reactions Of Aldehydes And Ketonesthe most common reactions are :Nucleophilic addition reactions

1- Reduction : Formation Of Alcohols


H

O

O

NaBH4

or LiAlH4

or H2 / Pd

NaBH4

or LiAlH4

or H2 / Pd

OH

OH

The reduction by NaBH4 , LiAlH4 ; the hydride ion H- is serve as nucleophile.

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2-Nucleophilic addition of Grignard reagent (formation of alcohols)

Addition of RMgX to formaldehyde gives 1◦ alc. Addition of RMgX to any other aldehyde gives 2◦ alc. Addition of RMgX to ketones gives 3◦ alc.

, dry ether+

2] H3O+

O CH3MgXCH3

OH1]

3- Oxidation reaction

Only aldehydes can be oxidized ketones resist oxidation

KMnO4

R

O

Hor

or K2Cr2O7Ar

O

H R

O

OHor

Ar

O

OH


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5-Addition of Hydrogen Cyanide: Formation Of Cynohydrins

+OHO

HCN CN

+ HCN

O

H

CN

OHBenzaldehyde cyanohydrin

R+ HCN

O

R'R

OH

R'

CNcyanohydrin


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6- Addition Of Alcohols:


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7- Addition of Ammonia and Ammonia Derivatives

145 Chem.

H3C

O

H

Aldehyde

NH2NH2

PhNHNH2

NH2OH

NH3

H3C

N

H

NH2

hydrazone

H3C

N

H

NHPh

phenylhydrazone

H3C

N

H

OH

Oxime

H3C

NH

H imine


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Exercises

1- The correct name of the following compound is: H

O

OHA) 3-hydroxyhexanalB) 3-hydroxy-4-hexenalC) 4-hydroxy-5-hexenalD)3-hydroxy-1-hexenal

2- The structure of Acetal is:

OC2H5

OH

OC2H5

OH

OH

OC2H5

OC2H5

OC2H5

OC2H5

A) B)

C) D)H

145 Chem.19


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145 Chem.20

3- Reaction of phenyhydrazine with carbonyl compounds (aldyhydes or ketones) gives:

A) Oxime B) Phenylhydrazone C) Imine D) Hemiacetal

4 - Which of the following compounds has the highest boiling point?

O

H

O OH OCH3A) B) C) D)


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Thank You for your kind attention !

Questions?

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1435-1436 2014-2015 Aldehydes and ketones 1. Learning Objectives Chapter eight introduces carbonyl...

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