aldehyde and ketone Flashcards
what are carbonyl group
organic compounds containing carbon-oxygen double bond (>C=O) called carbonyl group
explain carbonyl group in aldehyde and ketone
In aldehydes, the carbonyl group is bonded to a carbon and hydrogen while in the ketones, it is bonded to two carbon atoms
what is carboxylic acids
The carbonyl compounds in which
carbon of carbonyl group is bonded to carbon or hydrogen and oxygen of hydroxyl moiety (-OH) are known as carboxylic acids
what is amides and acyl halides
In compounds where carbon is attached to carbon or hydrogen and nitrogen of -NH2 moiety or to halogens are called amides and acyl halides
Esters and anhydrides are derivatives of _______
carboxylic acids
what uses Aldehydes, ketones and carboxylic acids have in nature
They play an important role in biochemical
processes of life. They add fragrance and flavour to nature, for example, vanillin (from vanilla beans), salicylaldehyde (from meadow sweet) and cinnamaldehyde (from cinnamon) have very pleasant fragrances. They are used in many food products and pharmaceuticals to add flavors
Nomenclature of Aldehydes and ketones
aldehydes often called by their common names instead of IUPAC names. The common names of most aldehydes are derived from the common names of the corresponding carboxylic acids by replacing the ending –ic of acid with aldehyde. The location of the substituent in the carbon chain is indicated by Greek letters alpha, beta, gamma, delta, etc.
The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. The locations of
substituents are indicated by Greek letters, a a’, b b’ and so on beginning with the carbon atoms next to the carbonyl group,
indicated as aa’
the simplest dimethyl ketone is called
acetone.
The name of the simplest aromatic aldehyde carrying the aldehyde group on a benzene ring is
benzene carbaldehyde or the common name benzaldehyde
Formaldehyde formula and real name
HCHO Methanal
Acetaldehyde formula and real name
CH3CHO Ethanal
Isobutyraldehyde formula and real name
(CH3)2CHCHO 2-Methylpropanal
Structure of the Carbonyl Group
The carbonyl carbon atom is sp2-hybridised and forms three sigma (s) bonds. The fourth valence electron of carbon remains in its p-orbital and forms a p-bond with oxygen by overlap with p-orbital of an oxygen In addition, the oxygen atom also has two non bonding electron pairs. the carbonyl carbon and the three atoms attached to it lie in the
same plane and the p-electron cloud is above and below this plane. The
bond angles are approximately 120° as expected of a trigonal coplanar
the carbonyl carbon acts an ________ and carbonyl oxygen acts an _________ and why
The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have substantial dipole moments and are polar than ethers
Preparation of Aldehydes and Ketones
By oxidation of alcohols
By dehydrogenation of alcohols
From hydrocarbons
(i) By ozonolysis of alkenes
(ii) By hydration of alkynes
Preparation of Aldehydes and Ketones By oxidation of alcohols
Aldehydes and ketones are generally prepared by oxidation of primary
and secondary alcohols, respectively
Preparation of Aldehydes and Ketones By dehydrogenation of alcohols
This method is suitable for volatile alcohols and is of industrial application. In this method alcohol vapours are passed over heavy metal catalysts (Ag or Cu). Primary and secondary alcohols give aldehydes and ketones, respectively
Preparation of Aldehydes and Ketones From hydrocarbons By ozonolysis of alkenes:
ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes ,ketones or a mixture of both depending on the substitution pattern of the alkene
Preparation of Aldehydes and Ketones From hydrocarbons By hydration of alkynes:
Addition of water to ethyne in the
presence of H2SO4 and HgSO4
gives acetaldehyde. All other
alkynes give ketones in this reaction
Preparation of Aldehydes
From acyl chloride (acid chloride)
From nitriles and esters
From hydrocarbons (i) By oxidation of methylbenzene
(ii) By side chain chlorination followed by hydrolysis
(iii) By Gatterman – Koch reaction
Preparation of Aldehydes From acyl chloride (acid chloride)
Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction.
Preparation of Aldehydes From nitriles and esters
Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give
corresponding aldehyde.
This reaction is called Stephen reaction.
nitriles are selectively reduced by
diisobutylaluminium hydride, (DIBAL-H) to imines followed by hydrolysis to aldehydes:
esters are also reduced to aldehydes with DIBAL-H.
Preparation of Aldehydes From hydrocarbons
By oxidation of methylbenzene
Strong oxidizing agents oxidize toluene and its derivatives to benzoic acids. However, it is possible to stop the oxidation at
the aldehyde stage with suitable reagents that convert the methyl group to an intermediate that is difficult to oxidize further
(a) Use of chromyl chloride (CrO2Cl2): Chromyl chloride oxidizes methyl group to a chromium complex, which on hydrolysis
gives corresponding benzaldehyde This reaction is called Etard reaction
(b) Use of chromic oxide (CrO3): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be
hydrolyzed to corresponding benzaldehyde with aqueous acid.
Preparation of Aldehydes By side chain chlorination followed by hydrolysis
Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method
of manufacture of benzaldehyde.
Preparation of Aldehydes By Gatterman – Koch reaction
When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminum chloride or cuprous chloride, it gives benzaldehyde or substituted
benzaldehyde.
Preparation of Ketones
From acyl chlorides
From nitriles
From benzene or substituted benzenes
Preparation of Ketones From acyl chlorides
Treatment of acyl chlorides with dialkylcadmium, prepared by the
reaction of cadmium chloride with Grignard reagent, gives ketones
Preparation of Ketones From nitriles
Treating a nitrile with Grignard reagent followed by hydrolysis yields a ketone.
Preparation of Ketones From benzene or substituted benzenes
When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminum chloride, it affords the corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction
Physical Properties of aldehydes and ketones
Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. The boiling points of aldehydes and ketones are higher than
hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding.
The lower members of aldehydes and ketones such as methanal, ethanal and propanone are miscible with water in all proportions, because they form hydrogen bond with water.
the solubility of aldehydes and ketones and smell of aldehydes and ketones
the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and ketones are
fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc. The lower aldehydes have sharp pungent odors. As the size of the molecule increases, the odour becomes less pungent
and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavoring agents.
Chemical Reactions with aldehydes and ketones
- Nucleophilic addition reactions
- Reduction
- Oxidation
- Reactions due to a-hydrogen
5 Cannizzaro reaction
6 Electrophilic substitution reaction
Chemical Reactions of aldehydes and ketones with Nucleophilic addition reaction(Mechanism of nucleophilic addition reactions)
A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp 2 hybridized orbitals of carbonyl carbon
The hybridization of carbon changes from sp2 to sp3 in this process, and a tetrahedral alkoxide intermediate is produced. This intermediate captures a proton from the
reaction medium to give the electrically neutral product. The net result is addition of Nu– and H+ across the carbon oxygen double bond
Chemical Reactions of aldehydes and ketones with Nucleophilic addition reaction(Reactivity)
Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in former
Some important examples of nucleophilic addition and nucleophilic addition-elimination reactions
(a) Addition of hydrogen cyanide (HCN):
(b) Addition of sodium hydrogen sulphite
(c) Addition of alcohols
(d) Addition of ammonia and its derivatives
Addition of hydrogen cyanide (HCN) to aldehydes and ketones
Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins. This reaction occurs very slowly with pure HCN. Therefore, it is catalyzed by a base and the generated cyanide ion (CN-) being a stronger nucleophile readily adds to
carbonyl compounds to yield corresponding
cyanohydrin.