NEET Study Notes for Carbonyl Compounds - Aldehydes, Ketones, and Carboxylic Acids with Solved Sample Questions

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Carbonyl Compounds is an important chapter from the NEET perspective when it comes to organic chemistry. On average, about 2 questions are asked every year from this topic making almost 3% of the chemistry part. It is important to go through these study notes before examinations to have a quick revision of the topic. Read More NEET Chemistry Syllabus

Organic Chemistry can be boring for many aspirants, but it also plays a major role in securing a medical seat. Therefore, it is important to study the topic thoroughly and have a quick look at the provided notes for the last time revision of NEET 2021.

Carbonyl Compounds Basics

Basic concepts of Carbonyl Compounds

Here we will discuss the basic concepts of Carbonyl Compounds, their definitions, basic formula & structure, and their methods of preparations.

Definitions of Carbonyl Compounds

Some basic definitions of different Carbonyl Compounds are tabulated below:

What are the Carbonyl Compounds?	The organic compounds containing carbon-oxygen double bond (>C=O) called carbonyl group, are known as Carbonyl Compounds.
What are Aldehydes?	The Carbonyl Compounds in which the Carbonyl group is attached to a carbon and hydrogen are called Aldehydes.
What are Ketones?	The Carbonyl Compounds in which the Carbonyl group is attached to two carbon atoms are called Ketones.
What are 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 are Acyl Halides?	The carbonyl compounds in which carbon is attached to carbon or hydrogen and halogens are called Acyl Halides.
What are Amides?	The carbonyl compounds in which carbon is attached to carbon or hydrogen and nitrogen of -NH2 moiety are called Amides.

General Formulas and Structures of Carbonyl Compounds:

The general formulas and structures of Carbonyl Compounds are given below:

Structure of the Carbonyl Group

The carbon in the Carbonyl Group is Sp2hybridized.
It forms three sigma (σ) bonds.
The fourth valence electron of Carbon forms - bond with oxygen.
The bond angles are approximately 120°.

Carbonyl Group Structure

Resonating structure of neutral (A) and dipolar (B) Carbonyl group.

The carbon-oxygen double bond (C=O) is highly polar due to the high difference between the electronegativity of Carbon and Oxygen.
Hence, the carbonyl carbon acts as an electrophile (Lewis acid) and the carbonyl oxygen acts as a nucleophile (Lewis base).

Sample Question

Question: In a polar carbonyl group, the carbonyl carbon and carbonyl oxygen act as ………

Lewis acid and Lewis Base
Lewis acid and nucleophile
Electrophile and Lewis Base
All of the above

Correct Answer: D. All of the above.

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Carbonyl Group Nomenclature

Nomenclature and Structure of Carbonyl Group

Two systems of nomenclature of Aldehydes and Ketones are generally used:

Common names
IUPAC names

Common nomenclature	IUPAC nomenclature
The common names of most of the aldehydes are derived from their respective carboxylic acids by replacing the “-ic” with “-aldehyde”.	Open chain aliphatic aldehydes and ketones are named by replacing the ending of the respective alkanes by –e with –al and –one respectively.
The position of the substituents is indicated by the Greek alphabets α, β, γ, δ, etc.	In the case of Aldehydes, the group containing the longest carbon chain is taken into consideration while numbering, starting from the carbon of the Aldehyde group.
The common names of Aldehydes are derived by naming alkyl or aryl groups that are bonded to the Carbonyl group.	In the case of Ketones, the numbering starts from the end near the carbonyl groups.
The positions of the substituents are indicated by Greek letters, α α′, β β′ and so on.	IUPAC names are widely accepted names and are universal.

Common and IUPAC names of some common Aldehydes and Ketones

Common and IUPAC names along with structure and formula are often asked as objective questions in exams. So, it is important to by heart all the common and IUPAC names of some of the common aldehydes and ketones.

Common and IUPAC names of common Aldehydes

Structure	Common name	IUPAC name
HCHO	Formaldehyde	Methanal
CH3CHO	Acetaldehyde	Ethanal
CH32CHCHO	Isobutyraldehyde	2-Methylpropanol
	γ-Methylcyclohexanecarbaldehyde	3-Methylcyclohexanecarbaldehyde
CH3CHOCH3CHO	α-Methoxypropionaldehyde	2-Methoxypropanal
CH3CH2CH2CH2CHO	Valeraldehyde	Pentanal
CH2=CHCHO	Acrolein	Prop-2-enal
	Phthalaldehyde	Benzene-1,2-dicarbaldehyde
	m-Bromobenzaldehyde	3-Bromobenzenecarbaldehyde or 3-Bromobenzaldehyde

Common and IUPAC names of Common Ketones

Structure	Common name	IUPAC name
CH3COCH2CH2CH2CH3	Methyl n-propyl ketone	Pentan-2-one
CH32CHCOCHCH32	Diisopropyl ketone	2,4-Dimethylpentan-3-one
	α-Methylcyclohexanone	2-Methylcyclohexanone
CH32C=CHCOCH3	Mesityl oxide	4-Methylpent-3-en-2-one

Sample Question

Question: The common and IUPAC name of CH3CH2CH2CH2CHOis…………….

Valeraldehyde and Pentanal
Acrolein and Pentanal
Valeraldehyde and 3-Bromobenzaldehyde
Acrolein and 3-Bromobenzaldehyde

Correct Answer: A. Valeraldehyde and Pentanal

Aldehydes & Ketones Prep

Preparation of Aldehydes and Ketones

The Aldehydes and Ketones are generally prepared by four different methods of preparations, which are described briefly below.

Methods of Preparation of Aldehydes and Ketones

Oxidation of Alcohols
- Primary Alcohols → Aldehydes
- Secondary Alcohols → Ketones

The following are the general methods of preparations of Aldehydes and Ketones from the alcohols:

Commonly used oxidizing agents:

KMnO4
K2Cr2O7
Collins Reagents (Chromium trioxide-pyridine complex CrO3)
PCC (pyridinium chlorochromate)

Dehydrogenation of Alcohols
- Primary Alcohols → Aldehydes
- Secondary Alcohols → Ketones
- It is suitable for volatile alcohol.
- It is an industrial method of preparation.
- For the conversion of valuable alcohols to aldehydes.
- It is the best method for the preparation of Aldehydes and Ketones as there is no risk of conversion to Carboxylic acids.

The Alcohols are passed through metal catalysts at 573 K temperature. The following reaction takes place during the procedure:

Ozonolysis of Alkenes
- The alkenes are first converted to Ozonoid by ozonolysis the addition of O3.
- Ozonoid is then converted to respective Aldehydes or Ketones by reduction using Zinc dust and water or H2/ Pd.
- The formation of Aldehydes and Ketones depends on the substitution arrangement of Alkene compounds.

Hydration of Alkynes
- Alkynes follow Markovnikov’s rule and produce Ketones in presence of a proper catalyst.
- All Alkynes, presence of HgSO4 and H2SO4, react with water to form Ketones.
- However, there is one exception due to the formation of aldehyde from ethyne.

Previous Year Sample Question

Some of the previous year sample questions for NEET are provided below:

Question: Which of the following reactions will not yield Aldehyde?

Correct Answer: B.

It gives ketone

Methods of Preparation of Aldehydes

From acyl chloride
- Acyl chloride (acid chloride) is hydrogenated over the catalyst, palladium on barium sulfate to form Aldehyde.
- This reaction is also called the Rosenmund reaction.

From nitriles and esters
- Nitrites are reduced to imines with stannous chloride in presence of hydrochloride.
- The imines produce respective Aldehydes on hydrolysis.
- This is also called the Stephen reaction.

Nitriles can also be reduced to imines with the help of DIBAL-H, followed by hydrolysis to form respective aldehydes.

Similarly, esters can also be reduced with the help of DIBAL-H to form aldehydes.

Etard reaction
- Methyl group is oxidized by Chromyl chloride to Chromium complex, which on hydrolysis gives corresponding benzaldehyde.

Sidechain halogenation followed by hydrolysis of toluene
- Benzal chloride is obtained by the side chain chlorination of toluene.
- Benzaldehyde is obtained by the hydrolysis of benzal chloride.
- This is the industrial method of benzaldehyde manufacturing.

Gattermann-Koch Synthesis
- Benzene or its derivative is treated with Carbon monoxide and HCL to form benzaldehyde or substituted benzaldehyde.
- This reaction takes place in the presence of Anhydrous aluminum chloride or cuprous chloride.

Sample Question

Question: Name the given reaction for the method of aldehyde preparation:

Reimer-Tiemann reaction
Cannizzaro reaction
Rosenmund reaction
Reformatsky reaction

Correct Answer: C. Rosenmund reaction

Methods of Preparation of Ketones

Generally, the following three methods of preparations are used to produce ketones.

From acyl chlorides
- Dialkyl Cadmium is prepared by the reaction of cadmium chloride with the Grignard reagent.
- Then, this Dialkyl Cadmium is allowed to react with acyl chlorides which give ketones.

From nitriles

Nitriles, on reaction with Grignard reagent followed by hydrolysis, give Ketones.

From benzene or substituted benzene
- Benzene or substituted benzene, on reaction with an acid chloride in presence of anhydrous aluminum chloride, yields Ketones.
- This reaction is also known as the Friedel-Crafts acylation reaction.

Sample Question

Question: What is the end product in the given chemical reaction?

Acetic acid
Isopropyl alcohol
Acetone
Ethanol

Correct Answer: C. Acetone

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Sample Questions

Sample Questions from previous years’ papers

The reaction between benzaldehyde and acetophenone in presence of dilute NaOH is known as …….
1. Cross Cannizzaro’s reaction
2. Cross Aldol condensation.
3. Aldol condensation
4. Cannizzaro’s condensation

Correct Answer: B. Cross Aldol condensation