Aldehydes And Ketones

ALDEHYDES AND KETONES

STRUCTURE

Ald h d Aldehyde O C R

H

R = H, alkyl, aryl

Ketone

O C R

R'

R and d R' = alkyl lk l or aryll R and R' cannot be hydrogen!

NOMENCLATURE

IUPAC Nomenclature of Ketones • Ch Choose th the llongestt continuous ti carbon b chain h i th thatt contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon • Ketone ending is -one

Do the ketones section of Organic g Nomenclature program!

EXAMPLES O C CH 3

CH 2 CH 2

CH 3

2-Pentanone

O C

CH3 CH2

CH2 CH

CH3

CH2 CH3 4-Ethyl-3-hexanone

O

CH

CH3

CH3 3-Isopropylcyclopentanone

KETONES

Common or Trivial Common, Trivial, Names • Name each group attached to the carbonyl group as an alkyl group • Combine into a name, according to the pattern:

alkyl lk l alkyl’ lk l’ ketone k t NOTE NOTE:

This is not all one word!

Example of Common Names O C CH 3

CH 2 CH 2

CH 3

Methyl propyl ketone

O CH3

C CH2

CH3 CH2

Diethyl ketone

SPECIAL CASES O

O

C

C

CH3

CH3

di th l ketone dimethyl k t

diphenyl ketone benzophenone

acetone A common laboratory solvent and cleaning agent g

KNOW THESE

O C CH3 methyl phenyl ketone acetophenone

IUPAC Nomenclature of Aldehydes • Choose the longest continuous carbon chain that contains t i the th carbonyl b l carbon b • Number from the end of the chain closest to the carbonyl carbon (carbon #1!) • Aldehyde ending is -al

Do the aldehydes section of Organic Nomenclature program.

EXAMPLES H3C

CH2

CH2 CH2

C

aldehyde group is always carbon 1

O

H pentanal

Cl 4

CH3

3

CH

1

2

C

CH CH3

O

H

2 chloro 3 methylbutanal 2-chloro-3-methylbutanal

Common Names of the Aldehydes

H

O

O

O

C

C

C

CH3

H

Formaldehyde 1

H3C CH2 C

H

H3C CH2

Acetaldehyde 2

H

Propionaldehyde 3

O

O

C

C H

H3C CH2 CH2 C

Butyraldehyde

Valeraldehyde

4

5

H

O C H3C CH2 CH2 CH2 CH2 Caproaldehyde 6

H

RECOGNIZE THESE

O

SPECIAL CASES

C H

H

O C H

formaldehyde

O

benzaldehyde

C H

CH3

acetaldehyde

KNOW THESE

Forming Common Names of Aldehydes USE OF GREEK LETTERS

C C ω ……. ε

C δ

O

C

C

C

C

γ

β

α

−−

H

ω is always the end of the chain, no matter how long CHO

CHO Cl α-chlorocaproaldehyde chlorocaproaldehyde ( α-chlorohexanal )

Cl ω-chlorocaproaldehyde chlorocaproaldehyde ( ω-chlorohexanal )

REACTIVITY OF THE C=O GROUP NUCLEOPHILIC ADDITION

GENERALIZED CHEMISTRY

THE CARBONYL GROUP nucleophilic att oxygen

.. δO:

C

electrophiles add here

H+ or E+

.. :O :

δ+

C +

Nu:

nucleophiles attack here electrophilic at carbon

NUCLEOPHILIC ADDITION TO C=O MECHANISMS IN ACID AND IN BASE

Nucleophilic Addition to Carbonyl Basic or Neutral Solution .. _ :O:

.. O:

-:Nu

+

slow C

C

an alkoxide ion

Nu .. _ :O:

.. :O H fast

C Nu

+

H2O

C

or on adding acid

Nu

Good nucleophiles and d strong t b bases (usually charged)

BASIC SOLUTION

Nucleophilic Addition to Carbonyl Acid Catalyzed + :O

.. O: C

+

+ H

fast C

.. :O

.. + O H

H

slow +

C

more reactive to addition than the unprotonated precursor

H

:Nu

C Nu

Acid catalysis speeds the rate of addition of weak k nucleophiles l hil and d weak bases (usually uncharged).

(+)

ACIDIC SOLUTION pH 5-6

stronger acid protonates the nucleophile

CYANOHYDRINS

Addition of Cyanide y Buffered to pH 6-8

:C

N:

.. _ :O :

:O : _ R

C

R

+

CN

R

C

R

CN .. _ :O : R

C CN

.. :O R

+

H2O

R

C

H R

CN

a cyanohydrin

-, In acid solution there would be littleACN cyanohydrin and HCN (g) would be a problem (poison).

CYANIDE ION BONDS TO HEMOGLOBIN .. N CYANIDE IS Cyanide bonds IS A POISON (irreversibly) to the C .. CH3 H3C

site (Fe II) where oxygen usually bonds.

N

N

You die Y di off suffocation lack of oxygen.

Fe N

N CH3

H3C

CH2CH2COOH

CH2CH2COOH

HCN is a gas that you can easily breathe into your lungs.

ORGANOMETALLICS

Synthesis of Alcohols

Addition of Organometallic Reagents .. _ + :O: M

:O : R

M

(R-MgBr)

+

ether

R

C R

(R-Li)

R

C

R

R

:R -

H2O + H

These reagents cannot exist in acid solution

.. :O R

alcohol l h l

C R

workup k step

H R

+

M (OH)x

Summary of Reactions of Organometallics with Carbonyl Compounds All review t you to

• Organometallics with ketones yield tertiary alcohols • Organometallics with aldehydes yield secondary alcohols • Organometallics with formaldehyde yield primary alcohols. • Organometallics with carbon dioxide yield carboxylic acids.

etc.

HYDRATES

Addition of Water O

O H

+ H +

C

H2O

R

R'

R

aldehyde or ketone favored

R

C O H

O R'

C R

+ R'

R'

O H a hydrate hydrates are unstable and cannot be isolated in most cases

most hydrates revert to an aldehyde or ketone as soon as they form O H

C

H2O

ACID CATALYSIS RECALL

H +

O H .. H .. + :O :O H

.. :O H +

Acid catalysis enhances the reactivity of the carbonyl group - nucleophilic addition proceeds more easily.

:Nu N weak nucleophiles can react

Water is a weak nucleophile.

WATER ADDS TO THE CARBONYL GROUP OF ALDEHYDES AND KETONES TO FORM HYDRATES H

catalyzed by a trace of acid

+

..

:O

H

O H

..

..

+ H :O

H

.. O ..

:O

H

..

H

C

C

O+ H .. H

:O ..

H

.. O ..

a hydrate

H

H

H

+

H for most compounds the equilibrium favors the starting g materials and you cannot isolate the hydrate

H

:O

O H

..

MICROREVERSIBILITY: In a reaction where all steps p are reversible, the steps in the reverse reaction are the same as those in the forward reaction, reversed!

ISOTOPE EXCHANGE REVEALS THE PRESENCE OF THE HYDRATE O18

O R

+H2O18

R

+ H2O

H+

18

R

excess

O H R C R 18 O

H

R

an excess off H2O18 shifts the equilibrium to the right

-H2O

exchange shows the presence of a symmetric intermediate

SOME STABLE HYDRATES these also indicate that hydrates y are possible p

δ− Cl δ−

Cl

C

δ+Cl δ−

Cl

O H

chloral

120o expected 60o required

O sp2 cyclopropanone l

Cl

OH

C

OH

Cl H chloral hydrate

OH sp3 OH

109o expected 60o required

cyclopropanone l hydrate

SOME ADDITIONAL STABLE HYDRATES O

O

O

H C C H

glyoxal

O

H

C C OH H O

O

Ph C C phenylglyoxal

H

Ph

OH

OH

C C OH H

ACETALS AND HEMIACETALS

ACID CATALYSIS RECALL

H +

O H .. H .. + :O :O H

.. :O H +

Acid catalysis enhances the reactivity of the carbonyl group - nucleophilic addition proceeds more easily.

:Nu N weak nucleophiles can react

Alcohols are weak nucleophiles.

Addition of Alcohols TWO MOLES OF ALCOHOL WILL ADD

addition of one mole

O

H+

R C R' + ROH

O H R C R'

hemiketal

O R addition of second mole

O H R C R' O R

H+

+

ROH

O R R C R' + H O O R

H

an aketal The equilibria normally favor the aldehyde or ketone starting material, but we will show how they can be made.

ACETALS AND HEMIACETALS R C O

ROH

H aldehyde

R C H

OH ROH OR

hemiacetal

R C O R

ketone

ROH

R C R

OH ROH OR

R

OR C

H

OR

acetal

R

OR C

R

OR

(h ik t l)* (hemiketal)*

(k t l)* (ketal)*

*older term

*older term

.. R OH

+ H 2S O4

R

O

+

H

Like a hydronium y ion

H

R

+

..

H O

:O

..

H

R C R

ACID CATALYZED FORMATION OF A HEMIACETAL

..

+

:O H R C R

H

.. O ..

R C R H

R

first addition

H

:O O+

..

R

..

: R O H ..

:O

Normally the starting material is favored but a second molecule of alcohol can react if in excess (next slide)

H H

R C R hemiacetal

O : ..

R

+ R O+

..

H

FORMATION OF THE ACETAL ( from the hemiacetal ) remove

R

+

H O ..

H

H

..

H

:O H

..

R C R

H O + R C R

:O ..

:O ..

R

.. O ..

H

H

: .. O

second addition

R

R C R

R C R

:O +

:O

SN1

R

R

+

R

hemiacetal

..

..

+ H

: R O H

:O R

R

H

R C R

:O ..

R

O:

H

..

O R

+

R C R

:O .. acetal

R

Resonance stabilized carbocation

STABILITY OF ACETALS AND HEMIACETALS Most hemiacetals are not stable, except for those of sugars (see later). later) Acetals are not stable in aqueous acid, but they are stable to aqueous base. base

AQUEOUS ACID

AQUEOUS BASE

C

OR H2SO4 OR

H2O

OR NaOH C OR H2O

ROH C O + ROH

no reaction

ADDITION OF WATER AND ALCOHOLS WATER

O

H2O

HO

OH

C

hydrate y

ALCOHOLS ROH R-O-H

O

ROH R-O-H

HO

RO

OR

C

H2O hemiacetal

RO

OR

OR

H+ H2O H2O

NaOH

O +2 ROH no reaction

acetal

acetals are stable to base but not to aqueous acid

REAKSI OKSIDASI

OKSIDASI ALDEHID DAN KETON • Keton tidak mudah dioksidasi • Aldehid sangat mudah dioksidasi dioksidasi, menjadi asam karboksilat Zat pengoksidasi : KMnO4, H, H2O

Reaksi Reduksi

Reaksi Reduksi • Reduksi aldehid menghasilkan alkohol primer • Reduksi keton menghasilkan alkohol sekunder • Zat pereduksi: H2 kkatalis H2, li Zn/Hg, HCl

Reaksi Adisi-eliminasi

Reaksi Adisi-eliminasi • Aldehid + Amina Primer • Aldehid + Amina sekunder • Aldehid + Amina tersier

Imina Enamina hidrazon

Ramalkan produk hemiasetal atau hemiasetal siklik dari:

11. 5-hidroksi-2-heksanon 5 hidroksi 2 heksanon dengan air 2. 1,3,4,5,6-pentahidroksi-2-heksanon dengan air 3. propanal dengan metanol 4. Aseton dengan 1,2,3-propanatriol

Ramalkan apa produk reaksi sikloheksanon dengan : 1. CH3NH2 2. (CH3)2NH