Chapters

The naming part of NCERT Class 11 Unit 8 (Organic Chemistry: Some Basic Principles and Techniques): classification of organic compounds, functional groups, homologous series and IUPAC nomenclature (sections 8.4–8.5), plus what JEE Main adds beyond the book (marked Beyond NCERT). The rest of the unit is in General Organic Chemistry, Isomerism and Practical Organic Chemistry.

Rule sheet

Every naming rule on one screen, for the last pass. Details and examples are in the sections below.

Step	Rule	Watch
Name's shape	prefixes + word root + (ene/yne) + suffix	Locant before each part
Principal group	highest in the priority list; the rest become prefixes	Halo, nitro, alkoxy, alkyl: prefixes only
Parent chain	contains the principal group, then most multiple bonds, then longest	Rings: see section 5
Numbering	lowest locant to principal group → multiple bonds → prefixes	First point of difference, not the sum
Tie, = vs ≡	the double bond gets the lower number	Only on an exact tie
Tie, prefixes	lower number to the first in alphabetical order	3-ethyl-6-methyl, not 6-ethyl-3-methyl
Alphabetical order	ignore di, tri, sec, tert; count iso, neo	sec-butyl under b, isopropyl under i
Same group twice	di, tri, tetra + commas between numbers	Ethane-1,2-diol keeps the "e"
Two or more C=C	drop the "ne": buta-1,3-diene
Chain C of –COOH, –CHO, –CN	is C1; suffix -oic acid, -al, -nitrile	On a ring: -carboxylic acid, -carbaldehyde
Benzene, disubstituted	o = 1,2; m = 1,3; p = 1,4	Three or more groups: numbers only
Homologous series	successive members differ by –CH₂– (14 u)	Same general formula

0 · What JEE Main asks from this chapter

33 questions in JEE Main 2019–2026, about 1 in every 5 papers, nearly all easy, all multiple choice. Grouped by type:

Type	Share	Typical question
Name a chain compound (one or more functional groups, enynes, esters)	~45%	IUPAC name of HC≡C–CH₂–CH(OH)–CH₂–CH=CH₂ (2025)
Benzene derivatives	~12%	3-Bromo-2-hydroxy-5-nitrobenzoic acid (2025)
Rings	~12%	3-Ethyl-1,1-dimethylcyclohexane (2024)
Common names and classes	~12%	Common name of benzene-1,2-diol: catechol (2024)
Structure from a name	~9%	Structure of 4-methylpent-2-enal (2024)
Priority order of functional groups	~6%	–SO₃H > –COCl > –CONH₂ > –CN (2022)
E/Z in a name	~3%	(2E)-2-Bromohex-2-en-4-yne (2021)

Five of the 33 are NCERT's own examples asked word for word (7-hydroxyheptan-2-one, 2,5,6-trimethyloctane, 3-ethyl-1,1-dimethylcyclohexane, 2,3-dibromo-1-phenylpentane, 4-ethyl-2-methylaniline). Know every named example in this unit.

1 · Classification of organic compounds

• Acyclic (open chain, aliphatic): straight or branched chains. Ethane, isobutane, acetaldehyde, acetic acid.
• Alicyclic (aliphatic cyclic): a ring that behaves like an aliphatic compound. Homocyclic if the ring is all carbon (cyclopropane, cyclohexane, cyclohexene); heterocyclic if another atom is in the ring (tetrahydrofuran).
• Aromatic: benzene and related rings (benzenoid: benzene, aniline, naphthalene); a ring without benzene that is still aromatic (non-benzenoid: tropone); aromatic rings with a heteroatom (heterocyclic aromatic: furan, thiophene, pyridine).
• Tetrahydrofuran is non-planar and not aromatic; furan is aromatic (asked 2022). Cyclohexene is alicyclic, not aromatic (asked 2024).

Bicyclo and spiro compounds · Beyond NCERT

• Bicyclo[x.y.z]alkane: two rings sharing two bridgehead carbons. x ≥ y ≥ z count the carbons in each bridge; the total is x + y + z + 2. Number from one bridgehead round the largest bridge, then the next, then the smallest. Bicyclo[2.2.1]heptane is norbornane.
• Spiro[a.b]alkane: two rings sharing one carbon. a ≤ b count the other carbons in each ring; the total is a + b + 1. Number from the smaller ring, next to the spiro atom. Spiro[3.3]heptane: two four-membered rings.

2 · Functional groups and homologous series

Functional group: an atom or group of atoms joined to the carbon chain that is responsible for the compound's characteristic chemical properties (–OH, –CHO, –COOH). Compounds with the same group react alike: CH₃OH, CH₃CH₂OH and (CH₃)₂CHOH all give H₂ with sodium.

Homologous series: a series of compounds with the same functional group. Members (homologues) share a general formula and differ in turn by –CH₂–. A compound with two or more functional groups is polyfunctional.

Series	General formula	First member
Alkane	CₙH₂ₙ₊₂	CH₄
Alkene	CₙH₂ₙ	C₂H₄
Alkyne	CₙH₂ₙ₋₂	C₂H₂
Alcohol, ether	CₙH₂ₙ₊₂O	CH₃OH; CH₃OCH₃
Aldehyde, ketone	CₙH₂ₙO	HCHO; CH₃COCH₃
Acid, ester	CₙH₂ₙO₂	HCOOH; HCOOCH₃

Example (2024) · The second homologue of the monocarboxylic acids is CH₃COOH, C₂H₄O₂ (the first is HCOOH).

Example (NCERT exercise 8.6) · First five from H–COOH: HCOOH, CH₃COOH, CH₃CH₂COOH, CH₃(CH₂)₂COOH, CH₃(CH₂)₃COOH. From CH₃COCH₃: add one CH₂ each time (butanone, pentanone, hexanone, heptanone).

3 · Common (trivial) names

Before IUPAC, compounds were named from their source or a property. Common names are still used when the systematic name is long. NCERT's Table 8.1:

Compound	Common name	IUPAC name
(CH₃)₂CHCH₃	isobutane	2-methylpropane
C(CH₃)₄	neopentane	2,2-dimethylpropane
CH₃CH₂CH₂OH	n-propyl alcohol	propan-1-ol
HCHO	formaldehyde	methanal
(CH₃)₂CO	acetone	propan-2-one (propanone)
CHCl₃	chloroform	trichloromethane
CH₃COOH	acetic acid	ethanoic acid
C₆H₅OCH₃	anisole	methoxybenzene
C₆H₅NH₂	aniline	benzenamine (aminobenzene)
C₆H₅COCH₃	acetophenone	1-phenylethan-1-one
CH₃OCH₂CH₃	ethyl methyl ether	methoxyethane

More names JEE uses · Beyond NCERT

Common name	Structure or IUPAC name
catechol / resorcinol / quinol	benzene-1,2- / 1,3- / 1,4-diol
o-, m-, p-cresol	methylphenols
ethylidene chloride	CH₃CHCl₂, 1,1-dichloroethane
ethylene dichloride	ClCH₂CH₂Cl, 1,2-dichloroethane
vinyl, allyl	CH₂=CH–, CH₂=CH–CH₂–
benzyl, benzal, benzo	C₆H₅CH₂–, C₆H₅CH=, C₆H₅C≡
glycol, glycerol	ethane-1,2-diol, propane-1,2,3-triol
citric acid	2-hydroxypropane-1,2,3-tricarboxylic acid

Greek letters in common names count from the carbon next to the functional group: α, then β, then γ. In butanal, CH₃CH₂CH₂CHO, α-methyl means 2-methyl. On a ring, the carbon carrying the group is α: γ-methylcyclohexanecarbaldehyde is 3-methylcyclohexanecarbaldehyde (2022). Aminobenzene and aniline are the same compound (2024).

4 · Naming alkanes

Hydrocarbons: only C and H. Saturated if all C–C bonds are single (alkanes, once called paraffins). Unsaturated if there is at least one C=C or C≡C.

Word roots (C1 to C4 come from trivial names):

C atoms	Root
1	meth
2	eth
3	prop
4	but
5	pent
6	hex
7	hept
8	oct
9	non
10	dec

Then undec (11), dodec (12), icos (20), triacont (30). An alkyl group is an alkane less one H: change -ane to -yl (CH₄ → –CH₃ methyl). Abbreviations: Me, Et, Pr, Bu.

Branched alkyl groups:

Name	Structure
isopropyl	(CH₃)₂CH–
sec-butyl	CH₃CH₂CH(CH₃)–
isobutyl	(CH₃)₂CHCH₂–
tert-butyl	(CH₃)₃C–
neopentyl	(CH₃)₃CCH₂–

NCERT's rules for branched alkanes:

1. Pick the longest chain as the parent.
2. Number it so the branched carbons get the lowest possible numbers.
3. Prefix the alkyl names with their locants, alphabetically. Numbers are separated from words by hyphens; the last prefix runs straight into the parent: 6-ethyl-2-methylnonane.
4. Identical groups take di, tri, tetra, penta, hexa, with commas between their numbers. These multipliers are not counted in the alphabetical order.
5. If two groups sit at equivalent positions, the lower number goes to the one first in the alphabet: 3-ethyl-6-methyloctane, not 6-ethyl-3-methyloctane.
6. A branched substituent is numbered from the carbon that joins the parent (that carbon is 1) and written in brackets: 5-(2,2-dimethylpropyl)nonane; 1,3-dimethylbutyl.
7. Two chains of equal length: take the one with more side chains. Then number from the end nearer a substituent.

In the alphabetical order iso and neo count as part of the name; sec and tert do not. So 5-sec-butyl-4-isopropyldecane: b before i. Iso names are allowed only while the group carries no further substituent.

Lowest locants compare the sets term by term and stop at the first point of difference; the sum doesn't matter. 2,7,8-trimethyldecane beats 3,4,9-trimethyldecane though 17 > 16.

Example (NCERT Problem 8.7, asked 2024) · CH₃CH(CH₃)CH₂CH₂CH(CH₃)CH(CH₃)CH₂CH₃ is 2,5,6-trimethyloctane, not 3,4,7-. Also from the problem: 3-ethyl-5-methylheptane (not 5-ethyl-3-methyl), and 5-(2-ethylbutyl)-3,3-dimethyldecane (not 5-(2,2-dimethylbutyl)-3-ethyldecane: the longer parent wins).

Example (2025) · (CH₃)₂C(C₃H₇)₂: the longest chain runs propyl–C–propyl, 7 carbons, with two methyls on C4 → 4,4-dimethylheptane. CH₃CH₂CH(C₂H₅)CH₂CH(CH₃)C₂H₅ → 3-ethyl-5-methylheptane.

Cyclic compounds: prefix cyclo- to the alkane with the same number of carbons, then apply the same rules.

Example (NCERT Problem 8.7, asked 2024) · A cyclohexane with two methyls on one carbon and an ethyl two carbons away is 3-ethyl-1,1-dimethylcyclohexane: locants {1,1,3} beat {1,3,3}.

5 · Naming compounds with functional groups

1. Find the functional group; it fixes the suffix.
2. Take the longest chain containing it, numbered so the group gets the lowest number.
3. In a polyfunctional compound, the principal functional group (highest priority) gives the suffix; the others are named as prefixes.

Priority, highest first (NCERT):

Acid anhydride (–CO–O–CO–) sits between –SO₃H and ester (Beyond NCERT). –R, C₆H₅–, halogens (F, Cl, Br, I), –NO₂ and alkoxy (–OR) are always prefixes.

Suffixes and prefixes (from NCERT's Table 8.4):

Class	Suffix (prefix)	Example
Carboxylic acid	-oic acid (carboxy)	butanoic acid
Sulphonic acid	-sulphonic acid (sulpho)	methanesulphonic acid
Carboxylate ion	-oate	sodium butanoate
Ester	alkyl -oate (alkoxycarbonyl)	methyl propanoate
Acid halide	-oyl halide (halocarbonyl)	butanoyl chloride
Amide	-amide (carbamoyl)	butanamide; N,N-dimethylethanamide
Nitrile	-nitrile (cyano)	pentanenitrile
Aldehyde	-al (formyl, oxo)	butanal
Ketone	-one (oxo)	butan-2-one
Alcohol	-ol (hydroxy)	butan-2-ol
Amine	-amine (amino)	butan-2-amine
Alkene, alkyne	-ene, -yne	but-1-ene, but-2-yne
Halide, nitro, ether	halo-, nitro-, alkoxy-	1-bromobutane, nitromethane, ethoxyethane

More rules:

• Several identical principal groups: di, tri before the suffix, and the parent keeps its full name: CH₂(OH)CH₂(OH) is ethane-1,2-diol.
• More than one C=C or C≡C: the "ne" of the parent is dropped: CH₂=CH–CH=CH₂ is buta-1,3-diene.
• A carbon that is part of –COOH, –CHO, –CN, –COCl, –CONH₂ or –COOR is counted in the chain and numbered 1.
• A prefix-only group never takes the low number from a multiple bond: BrCH₂CH=CH₂ is 3-bromoprop-1-ene, not 1-bromoprop-2-ene.

Example (NCERT, asked 2024) · HOCH₂(CH₂)₃CH₂COCH₃ is 7-hydroxyheptan-2-one, not 2-oxoheptan-7-ol: the ketone outranks the alcohol.

Example (NCERT Problem 8.8) · 6-Methyloctan-3-ol (–OH on C3, methyl on C6). Hexane-2,4-dione (two keto groups). 5-Oxohexanoic acid (CH₃CO(CH₂)₃COOH: the acid is C1, the keto at C5 is "oxo"). Hexa-1,3-dien-5-yne (CH₂=CH–CH=CH–C≡CH).

Example (NCERT Problem 8.9) · 2-Chlorohexane is CH₃CH₂CH₂CH₂CH(Cl)CH₃. Pent-4-en-2-ol is CH₂=CHCH₂CH(OH)CH₃. 6-Hydroxyheptanal is CH₃CH(OH)CH₂CH₂CH₂CH₂CHO; the CHO carbon is C1. In 3-nitrocyclohexene the C=C takes C1 and C2, because –NO₂ is only a prefix. In cyclohex-2-en-1-ol, –OH takes C1, because a suffix group outranks the C=C (asked 2024).

Example (2019) · CH₃CH(CH₃)CH(OH)CH₂COOH is 3-hydroxy-4-methylpentanoic acid: COOH is C1, and hydroxy comes before methyl alphabetically.

Example (2024) · CH₃CH(NH₂)CH₂CN is 3-aminobutanenitrile: the CN carbon is C1.

Example (2025) · HC≡C–CH₂–CH(OH)–CH₂–CH=CH₂ is hept-1-en-6-yn-4-ol. –OH is C4 from either end; the multiple bonds are {1,6} either way, so the double bond takes the 1.

Example (2025) · BrCH₂–C(CH₃)=CH–CH₃ is 1-bromo-2-methylbut-2-ene. The C=C is at 2 from either end; the prefixes decide: {1,2} beats {3,4}.

Chain, multiple bonds and the tie rule · Beyond NCERT

• JEE keys take the chain with the most multiple bonds before the longest one. (IUPAC's 2013 rules put length first, but JEE has not moved.)
• Number to give the lowest locants to the multiple bonds as a set, double and triple together. Only on an exact tie does the double bond get the lower number: pent-1-en-4-yne, but pent-3-en-1-yne (the set {1,3} beats {2,4}).

Example (2019) · CH₂=CH–CH(CH₃)–CH(C₃H₇)–CH(CH₃)–C≡CH is 3,5-dimethyl-4-propylhept-1-en-6-yne: the 7-carbon chain holds both multiple bonds, {1,6} either way, so the double bond takes 1.

Example (2021) · CH₃–C(Br)=CH–C≡C–CH₃ with Br and the C≡C–CH₃ group on opposite sides of the C=C is (2E)-2-bromohex-2-en-4-yne. E/Z (Isomerism) is written in brackets at the front.

Rings with a functional group · Beyond NCERT

• A suffix group on a ring takes C1: cyclohex-2-en-1-ol; 4-ethylcyclopent-2-en-1-ol (2025).
• When –COOH, –CHO or –CN hangs on a ring, its carbon is not counted: cyclohexanecarboxylic acid, cyclohexanecarbaldehyde, cyclohexanecarbonitrile. 4-Bromo-2-methylcyclopentane-1-carboxylic acid (2020).
• If a chain carries the principal group, the ring is a substituent (cyclohexyl, phenyl).

Esters, ethers, amides · Beyond NCERT

• Ester R–COO–R′: alkyl (R′) first, then the acid name with -oate. CH₃COOC₂H₅ is ethyl ethanoate. CH₃CH₂CH(CH₃)CH₂CH₂CH(Br)COOCH₂CH₂CH₃ is propyl 2-bromo-5-methylheptanoate (2026).
• When an ester is not the principal group, –COOR is "alkoxycarbonyl" (methoxycarbonyl).
• Ether R–O–R′: the larger group is the parent, the smaller is alkoxy: CH₃OC₃H₇ is 1-methoxypropane.
• Amide or amine with groups on N: prefix N-: N,N-dimethylethanamide, N-methylethanamine.

6 · Substituted benzene

• Substituents are prefixed to "benzene": methylbenzene (toluene), methoxybenzene (anisole), aminobenzene (aniline), nitrobenzene, bromobenzene.
• Two substituents: number the ring so they get the lowest numbers: 1,3-dibromobenzene, not 1,5-. Trivial prefixes: ortho (o-) = 1,2; meta (m-) = 1,3; para (p-) = 1,4.
• Three or more: numbers only, by the lowest-locant rule; the names go alphabetically.
• A common name as the parent (anisole, aniline, phenol, benzoic acid, benzaldehyde, toluene): the carbon carrying that group is C1; then number towards the next substituent.
• A benzene ring on a chain that carries the functional group is a substituent: phenyl (C₆H₅–, Ph).

Example (NCERT) · 1-Chloro-2,4-dinitrobenzene (not 4-chloro-1,3-dinitrobenzene: {1,2,4} either way, so chloro takes 1 alphabetically; asked 2024). 2-Chloro-1-methyl-4-nitrobenzene (asked 2019). 2-Chloro-4-methylanisole. 4-Ethyl-2-methylaniline (asked 2024). 3,4-Dimethylphenol.

Example (2025) · Benzoic acid with –OH next to COOH, Br on the other side of the –OH and NO₂ para to the –OH: COOH is C1, so 3-bromo-2-hydroxy-5-nitrobenzoic acid.

Example (NCERT Problem 8.10) · o-Ethylanisole: OCH₃ and C₂H₅ on adjacent carbons. p-Nitroaniline: NH₂ and NO₂ at 1,4. 2,3-Dibromo-1-phenylpentane: C₆H₅CH₂CHBrCHBrCH₂CH₃ (asked 2024). 4-Ethyl-1-fluoro-2-nitrobenzene.

7 · Traps

Trap	What goes wrong	Do this
Lowest locants	Adding the numbers	Compare term by term; first difference wins
Alphabetical order	Filing "dimethyl" under d	Ignore di/tri, sec/tert; count iso, neo
Bracketed substituent	Ignoring "di" inside it	(1,2-dimethylpropyl) is filed under d
Ketone + alcohol	Naming it 2-oxo…-ol	The higher group is the suffix: 7-hydroxyheptan-2-one
Ene vs yne	Always numbering the double bond first	Lowest set first; the double bond wins only a tie
Halo vs C=C	1-bromoprop-2-ene	The C=C gets the lower number: 3-bromoprop-1-ene
–CHO / –COOH carbon	Not counting it in the chain	It is C1; on a ring use -carbaldehyde / -carboxylic acid
Ester name	2-bromo-5-methylpropanoate	Alkyl of the O side first, then the acid's chain
Priority lists	–CONH₂ above –COCl, or –CHO below C=O	Acid > SO₃H > ester > acid chloride > amide > nitrile > aldehyde > ketone
Benzene, 3 groups	Using o/m/p	Numbers only; a common-name parent group is C1

8 · Names worth knowing

• The ten word roots (meth to dec) and the five branched groups (isopropyl, sec-butyl, isobutyl, tert-butyl, neopentyl).
• The priority list, down to C≡C.
• Catechol, resorcinol, quinol; anisole, aniline, phenol, toluene, acetophenone; acetone, formaldehyde, chloroform.
• General formulas: alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂.

9 · For the boards only

JEE Main doesn't ask this, but the CBSE paper can.

• Citric acid is named from citrus fruits; formic acid from formica, Latin for ant (it is found in red ants).
• Buckminsterfullerene, the C₆₀ cluster, is named after the architect R. Buckminster Fuller, whose geodesic domes it resembles.
• Paraffin, the old name for alkanes, means "little affinity" (Latin).
• IUPAC stands for the International Union of Pure and Applied Chemistry; a systematic name lets the reader deduce the structure.