Chemistry Class 12 Part II…
🏠 Home Log in
TOPIC 9 OF 25

Nomenclature Structure Preparation

🎓 Class 12 Chemistry CBSE Theory Ch 8 – Aldehydes, Ketones and Carboxylic Acids ⏱ ~14 min
🌐 Language:

This MCQ module is based on: Nomenclature Structure Preparation

This assessment will be based on: Nomenclature Structure Preparation

Upload images, PDFs, or Word documents to include their content in assessment generation.

Nomenclature Structure Preparation

Introduction: The Carbonyl Family L1

From the vanillin that flavours ice-cream to the acetic acid that gives vinegar its bite, three families of organic compounds dominate the chemistry of the carbonyl group (>C=O). When this group is bonded to at least one hydrogen, we get an aldehyde (R–CHO); when bonded to two carbon groups, a ketone (R–CO–R'); and when bonded to a hydroxyl, a carboxylic acid (R–COOH).

Aldehyde R–CHO R = H or alkyl/aryl Ketone R–CO–R' R, R' = alkyl/aryl Carboxylic Acid R–COOH R = H or alkyl/aryl
Fig. 8.1: General formulae of the three carbonyl families.

8.1 Nomenclature & Structure of Carbonyl Group L2

8.1.1 Nomenclature of Aldehydes & Ketones

Aldehydes get common names from the corresponding carboxylic acid by replacing the -ic acid ending with -aldehyde. Ketones are often named by writing the two alkyl/aryl groups attached to the carbonyl carbon as separate words followed by 'ketone'.

The IUPAC names of open-chain aliphatic aldehydes and ketones are derived from the names of the corresponding alkanes by replacing the -e of alkane with -al for an aldehyde and -one for a ketone. The longest carbon chain is numbered starting from the end nearer to the carbonyl group. For cyclic ketones the suffix -one is added to the cycloalkane name.

Table 8.1 (selected): Common & IUPAC names
StructureCommon nameIUPAC name
HCHOFormaldehydeMethanal
CH3CHOAcetaldehydeEthanal
(CH3)2CHCHOIsobutyraldehyde2-Methylpropanal
C6H5CHOBenzaldehydeBenzenecarbaldehyde
CH3COCH2CH2CH3Methyl n-propyl ketonePentan-2-one
(CH3)2CHCOCH(CH3)2Diisopropyl ketone2,4-Dimethylpentan-3-one
Cyclohexanoneα-Methylcyclohexanone2-Methylcyclohexanone
(CH3)2C=CHCOCH3Mesityl oxide4-Methylpent-3-en-2-one

8.1.2 Structure of the Carbonyl Group

The carbonyl carbon is sp²-hybridised and forms three σ bonds in the same plane. The remaining p-orbital overlaps side-on with the p-orbital of oxygen to form the π component of the C=O double bond. Because oxygen is more electronegative than carbon, the C=O bond is highly polar: the carbon carries a δ⁺ charge while the oxygen carries a δ⁻ charge.

C O δ⁺ δ⁻ R R'/H π-cloud (above & below plane) ~120°
Fig. 8.2: sp² carbonyl carbon — three σ bonds at ~120° and a π bond above and below the plane.
Consequence of the polar C=O: the δ⁺ carbon is attacked by nucleophiles and the δ⁻ oxygen by electrophiles or H⁺. This single fact underlies every chemical reaction of aldehydes and ketones discussed in Part 2.
Activity 8.1 — Predict the Polarity Pattern

Setup: Three carbonyl compounds are placed in an electric field: acetone, propanal, and benzaldehyde.

Predict: Which end of each C=O bond will orient toward the positive plate? Which end of these molecules carries the largest δ⁺ on carbon — the one with two EDGs (acetone), one EDG (propanal), or an EWG benzene ring (benzaldehyde)?

In every C=O, the δ⁻ oxygen orients toward the positive plate and δ⁺ carbon toward the negative plate.

The δ⁺ character on carbon increases as electron-donating groups (alkyl) are replaced by H or by electron-withdrawing groups. Order of electrophilicity at carbonyl C:

HCHO > CH3CHO > CH3COCH3

Benzaldehyde is less reactive than HCHO because the lone pair of the ring can donate by resonance into C=O, reducing δ⁺.

8.2 Preparation of Aldehydes & Ketones L3

8.2.1 From Alcohols (oxidation / dehydrogenation)

Primary alcohols are oxidised to aldehydes (and further to acids). To stop at the aldehyde stage a mild oxidant such as PCC (pyridinium chlorochromate in CH2Cl2) is used. Secondary alcohols give ketones with K2Cr2O7/H2SO4.

R–CH2–OH  PCC→  R–CHO      R2CH–OH  K2Cr2O7/H2SO4→  R2C=O

Alcohols can also be dehydrogenated by passing vapour over heated Cu at 573 K — useful in industry because it gives clean aldehyde from a 1° alcohol.

8.2.2 From Hydrocarbons

(a) Ozonolysis of alkenes. Cleavage of C=C with O3 followed by Zn / H2O yields a pair of carbonyl compounds (Class 11 recap).

(b) Hydration of alkynes. Alkynes add water in presence of HgSO4/H2SO4 via Markovnikov addition. Ethyne gives ethanal; all other alkynes give ketones.

CH≡CH + H2O  HgSO4, H2SO4→  [CH2=CHOH] → CH3CHO

8.2.3 Preparation of Aldehydes Only

(a) From acyl chlorides — Rosenmund reduction

Rosenmund reduction uses H2 over a Pd/BaSO4 catalyst that is partly poisoned with sulphur, halting reduction at the aldehyde:

R–COCl + H2  Pd / BaSO4→  R–CHO + HCl

(b) From nitriles — Stephen reaction & DIBAL-H

Stephen reaction: RCN + SnCl2/HCl → RCH=NH → hydrolysis → RCHO. Alternatively, DIBAL-H (diisobutylaluminium hydride) reduces a nitrile or ester to an aldehyde at low temperature.

RC≡N  (i) AlH(i-Bu)2 (ii) H2O→  RCHO

(c) From hydrocarbons — Etard & Gattermann-Koch

Etard reaction oxidises the methyl group of toluene with CrO2Cl2 in CS2; hydrolysis of the resulting chromium complex yields benzaldehyde. Gattermann-Koch synthesis formylates benzene with CO + HCl in presence of anhydrous AlCl3 (and CuCl) to give benzaldehyde.

C6H5CH3 Toluene CrO2Cl2, CS2 then H3O⁺ C6H5CHO Benzaldehyde (Etard) C6H6 CO + HCl anhyd. AlCl3, CuCl C6H5CHO Benzaldehyde (Gattermann-Koch)
Fig. 8.3: Two industrial-style routes to benzaldehyde.

8.2.4 Preparation of Ketones

(a) From acyl chlorides: Treatment with dialkylcadmium R2Cd (from Grignard + CdCl2) gives ketones cleanly without further reaction.

2 R–COCl + R'2Cd → 2 R–CO–R' + CdCl2

(b) From nitriles: Grignard reagent adds to RC≡N giving an imine salt which on acid hydrolysis yields a ketone.

RC≡N + R'MgX → R–C(NMgX)=R'  H3O⁺→  R–CO–R' + NH3

(c) From benzene / substituted benzenes — Friedel-Crafts acylation: An acyl chloride (or acid anhydride) reacts with an arene in presence of anhydrous AlCl3 to give an aryl alkyl ketone.

C6H6 + RCOCl  anhyd. AlCl3→  C6H5COR + HCl
Worked Example 8.1 — IUPAC names L2

Give IUPAC names of (i) CH3CH(CH3)CH2CH2CHO, (ii) CH3CH2COCH(C2H5)CH2CH2Cl, (iii) CH3CH=CHCHO.

(i) Longest chain: 5 C with CHO at end. Numbering 1→5 from CHO. Methyl at C-4 → 4-methylpentanal.

(ii) Longest chain through C=O is 6 carbons (hex); numbering from end giving C=O lower locant → ketone at C-3. C-4 bears an ethyl, C-6 a chloro → 6-chloro-4-ethylhexan-3-one.

(iii) Four-carbon chain with C=O at end (al) and C=C between C-2 and C-3 → but-2-enal.

Worked Example 8.2 — Mechanism connection L4

Predict the major product when phenylmagnesium bromide is added to benzonitrile, followed by aqueous workup.

C6H5C≡N + C6H5MgBr → an imine salt (C6H5)(C6H5)C=NMgBr → hydrolysis gives the ketone diphenyl ketone (benzophenone) + NH3.

Interactive: Reagent → Carbonyl Product Predictor

Choose a starting material and a reagent; the simulator outputs the carbonyl produced.

Choose a starting material and reagent.

Intext Practice L3

Intext 8.1 — Writing structures

Write the structures of the following compounds: (i) α-Methoxypropionaldehyde, (ii) 3-Hydroxybutanal, (iii) 2-Hydroxycyclopentanecarbaldehyde, (iv) 4-Oxopentanal, (v) Di-sec-butyl ketone, (vi) 4-Fluoroacetophenone.

(i) CH3OCH(CH3)CHO   (ii) CH3CH(OH)CH2CHO   (iii) Cyclopentane with -OH at C-2 and -CHO at C-1.

(iv) CH3COCH2CH2CHO   (v) (CH3CH2)(CH3)CH–CO–CH(CH3)(CH2CH3)   (vi) 4-F-C6H4COCH3.

Competency-Based Questions

Q1. Why is the carbonyl carbon δ⁺ while the carbonyl oxygen is δ⁻? L2
Oxygen is more electronegative than carbon, so the σ and π electron clouds of the C=O bond are pulled toward O. This polarisation places a partial positive charge on C and a partial negative charge on O.
Q2. Identify the IUPAC name of CH3COCH2COOC2H5. L3
  • (a) Ethyl 3-oxobutanoate
  • (b) Ethyl 2-oxobutanoate
  • (c) Methyl ethanoate
  • (d) 3-Oxobutanoic acid
(a) Ethyl 3-oxobutanoate — the ester is the principal group (suffix -oate); the chain is butanoate; the keto group on C-3 is named oxo.
Q3. Which reagent will convert benzonitrile to benzaldehyde? L3
  • (a) NaBH4
  • (b) SnCl2/HCl then H2O
  • (c) LiAlH4
  • (d) H2/Ni
(b) Stephen reaction. SnCl2/HCl reduces to an aldimine; aqueous hydrolysis yields the aldehyde. NaBH4 does not reduce nitriles; LiAlH4/H2/Ni go all the way to primary amine.
Q4. Explain why Gattermann-Koch reaction fails for phenol. L4
Phenol's -OH coordinates strongly with AlCl3, deactivating the Lewis acid catalyst that is required to generate the formyl cation. The complexation removes the catalyst from the active cycle, so the formylation does not proceed.
Q5. Suggest a synthetic route from but-1-ene to butan-2-one. L6
Markovnikov hydration of but-1-ene (H2O/H2SO4) gives butan-2-ol; oxidation with K2Cr2O7/H2SO4 yields butan-2-one. Alternative single-step: hydration of but-1-yne with HgSO4/H2SO4 (after dehydrohalogenation of 2-bromobutane to but-1-yne).

Assertion–Reason Questions

Options: (A) Both A & R true; R correct explanation of A. (B) Both true; R not correct explanation. (C) A true, R false. (D) A false, R true.

A1. The carbonyl carbon is electrophilic.

R1. The C=O π-bond is polarised with carbon bearing a partial positive charge due to higher electronegativity of oxygen.

Answer: (A) — both true and R correctly explains A.

A2. Rosenmund reduction is used to convert acyl chlorides into aldehydes.

R2. The Pd/BaSO4 catalyst is partly poisoned so further reduction of the aldehyde to an alcohol is suppressed.

Answer: (A) — both true and R correctly explains A.

A3. The bond angle in the carbonyl group is ~120°.

R3. The carbonyl carbon is sp³ hybridised.

Answer: (C) — assertion true, reason false. Carbonyl C is sp² (not sp³), which is why bond angles are ~120°.

Frequently Asked Questions - Nomenclature Structure Preparation

What is the main concept covered in Nomenclature Structure Preparation?
In NCERT Class 12 Chemistry Chapter 8 (Aldehydes, Ketones and Carboxylic Acids), "Nomenclature Structure Preparation" covers the core chemistry principles and reactions students need for board exam success. The MyAiSchool lesson explains the topic with definitions, structural diagrams, reaction mechanisms, worked examples, and interactive simulations. Key reactions, IUPAC names, and chemical reasoning are highlighted throughout aligned with CBSE 2025-26 syllabus.
How is Nomenclature Structure Preparation useful in real-life or applied chemistry?
Real-life applications of "Nomenclature Structure Preparation" from NCERT Class 12 Chemistry Chapter 8 include drug design, polymer industry, food chemistry, electrochemical cells, fuel cells, dyes/pigments, agrochemicals, and biochemistry. The MyAiSchool lesson links every concept to a tangible industrial or biological example so students see chemistry as a problem-solving framework for the molecular world.
What are the key reactions students should memorize for Nomenclature Structure Preparation?
Key reactions in "Nomenclature Structure Preparation" (NCERT Class 12 Chemistry Chapter 8 Aldehydes, Ketones and Carboxylic Acids) are tabulated in the MyAiSchool reaction map. Students should memorize each reaction with its reagent, conditions, mechanism class (SN1/SN2/E1/E2/electrophilic addition/etc), product, and stereochemistry. The Summary section provides a quick-reference reaction chart for last-minute revision.
How does this part connect to other parts of Chapter 8?
NCERT Class 12 Chemistry Chapter 8 (Aldehydes, Ketones and Carboxylic Acids) is structured so each part builds chemical understanding sequentially. "Nomenclature Structure Preparation" connects to neighbouring parts via shared functional groups, reaction mechanisms, and structural concepts. The MyAiSchool lesson cross-references related concepts with internal links so students can navigate the whole chapter as one connected story rather than disconnected fragments.
What types of CBSE board questions come from Nomenclature Structure Preparation?
CBSE board questions from "Nomenclature Structure Preparation" typically include: (1) 1-mark MCQs on definitions and IUPAC naming, (2) 2-mark short-answer reactions/products, (3) 3-mark mechanism questions, (4) 5-mark long-answer combining mechanism + product + stereochemistry + application. The MyAiSchool lesson tags each Competency-Based Question (CBQ) with Bloom level (L1-L6) so students know how to study for each weight.
How can students use the interactive simulation effectively?
The interactive simulation in the "Nomenclature Structure Preparation" lesson allows students to explore reaction outcomes, predict products, or compare reaction conditions, with live visual feedback. To use it effectively: (1) try every option/configuration, (2) compare with the analytical reasoning, (3) check IUPAC names and structural correctness, (4) test edge cases from worked examples. The simulation reinforces conceptual intuition that pure mechanism memorisation cannot provide.
AI Tutor
Chemistry Class 12 Part II – NCERT (2025-26)
Ready
Hi! 👋 I'm Gaura, your AI Tutor for Nomenclature Structure Preparation. Take your time studying the lesson — whenever you have a doubt, just ask me! I'm here to help.

📝 Practice this topic — Mock Exams

🎯 Practise Chemistry

Sit a full paper on what you have been studying, marked question by question.

Mock exams

All mock exams for this subject →

🎁 Join our community and get free AI credits!
WhatsApp