Some Basic Principles of Organic Chemistry Formula Sheet — JEE Main Chemistry

Every key Some Basic Principles of Organic Chemistry formula, definition and theorem for JEE Main Chemistry in one place — with common examiner traps and worked examples. Free to read; blurt from memory, then check your gaps.

Syllabus — topics coveredNTA · 18 sub-topics

Tetravalency of carbon
Shapes of simple molecules
Hybridization (s and p)
Classification of organic compounds based on functional groups
Compounds containing halogens, oxygen, nitrogen and sulphur
Homologous series
Isomerism: structural and stereoisomerism
Nomenclature: trivial and IUPAC
Covalent bond fission: homolytic and heterolytic
Free radicals, carbocations and carbanions
Stability of carbocations and free radicals
Electrophiles and nucleophiles
Electronic displacement in covalent bond
Inductive effect
Electromeric effect
Resonance and hyperconjugation
Common types of organic reactions
Substitution, addition, elimination and rearrangement

Tetravalence, Hybridisation & Shapes

Tetravalence & catenation: Carbon has four valence electrons, so it forms

four covalent bonds

(tetravalent), and its strong C–C bonds let it

catenate

into long chains and rings — the basis of the vast number of organic compounds.

s p^{3}

tetrahedral,

109. 5^{\circ}

— e.g.

C H_{4}

s p^{2}

trigonal planar,

12 0^{\circ}

— e.g.

C_{2} H_{4}

s p

linear,

18 0^{\circ}

— e.g.

C_{2} H_{2}

★ Remember · s-character controls electronegativity & bonds

s-character:

s p (50%) > s p^{2} (33%) > s p^{3} (25%)

. More s-character pulls the orbital

closer to the nucleus

— so the carbon is more electronegative and the bond is

shorter and stronger

🎯 Exam · σ vs π bonds

σ

bond forms by

head-on

overlap (free rotation). A

π

bond forms by

sideways

overlap of p orbitals — its cloud lies above/below the plane, rotation about

C = C

restricted

, and

π

bonds are the

reactive sites

Counting σ and π

▸A single bond $= 1 σ$ ; a double bond $= 1 σ + 1 π$ ; a triple bond $= 1 σ + 2 π$ .
▸Every bond (single, double or triple) contains exactly $one$ $σ$ bond.
▸Restricted $C = C$ rotation is what makes geometrical (cis/trans) isomerism possible.

🚫 Examiner Trap · Examiner traps

(1) s-character

s p (50%) > s p^{2} (33%) > s p^{3} (25%)

\Rightarrow

more s means shorter, stronger bond and a more electronegative carbon. (2) Single

= 1 σ

, double

= 1 σ + 1 π

, triple

= 1 σ + 2 π

— EVERY bond has exactly one

σ

. (3)

π

bonds (sideways overlap) are the reactive sites and block rotation. (4) Restricted C

=

C rotation is what makes cis/trans isomerism possible.

Structural Representation & Classification

Four ways to draw butane: complete, condensed, bond-line and wedge-dash (3-D).

Ways to draw a structure

▸ $Complete$ : every bond drawn (Lewis/dash formula).
▸ $Condensed$ : omit some/all bonds — $C H_{3} C H_{2} C H_{2} C H_{3}$ .
▸ $Bond-line$ : zig-zag lines; line ends & junctions are carbons, only heteroatoms are written, chain ends are $C H_{3}$ .
▸ $Wedge-dash$ (3-D): solid wedge $=$ toward viewer, dashed $=$ away, plain line $=$ in plane.

Functional group & homologous series: A

functional group

(

- OH

- CHO

- COOH

…) is the reactive site that fixes a compound's chemistry. A

homologous series

is a family sharing that group whose members differ by a

- C H_{2} -

unit and show a graded change in properties.

★ Remember · Classification map

Acyclic

(open-chain

=

aliphatic) vs

Cyclic

(ring). Rings split into

homocyclic

— alicyclic (cyclohexane) or aromatic (benzenoid like benzene, non-benzenoid like tropolone) — and

heterocyclic

(a hetero atom in the ring: furan, thiophene, pyridine).

🎯 Exam · Aromatic ≠ just 'has a ring'

Aromatic compounds are a special, especially stable class (benzene and relatives). A ring with only single bonds (e.g. cyclohexane) is

alicyclic

, not aromatic.

🚫 Examiner Trap · Examiner traps

(1) In a bond-line structure, every line END and junction is a carbon, terminals are C

H_{3}

, and only heteroatoms are written. (2)

Aromatic

\neq =

'just a ring' — cyclohexane is

alicyclic

, not aromatic. (3) A homologous series shares a functional group and differs by

- C H_{2} -

. (4) Wedge

=

toward you, dash

=

away (3-D).

IUPAC Nomenclature I — The System

Anatomy of an IUPAC name broken into prefix, root, saturation and suffix using 4-methylpentan-2-ol as the example, with the chain-numbering rules listed below — An IUPAC name $=$ prefix $+$ root $+$ saturation $+$ suffix.

Building an IUPAC name: Identify the

parent hydrocarbon

(longest chain) and the functional group, then assemble:

word root

(chain length: meth, eth, prop, but, pent…)

+

suffix

(saturation

-

ane/

-

ene/

-

yne plus any functional-group suffix)

+

prefix

(substituents with locants).

Alkyl groups

▸Drop $-$ ane, add $-$ yl: $C H_{4} \to$ methyl, $C_{2} H_{6} \to$ ethyl.
▸Branched: $isopropyl, sec-butyl, isobutyl, tert-butyl, neopentyl$ .
▸ $iso$ - and $neo$ - count in alphabetising; $sec-$ and $tert-$ do not.

★ Remember · The numbering rules

(1)

Longest chain

=

parent. (2) Number so the branch/principal group gets the

lowest set of locants

. (3) Cite substituents

alphabetically

(ignore di/tri prefixes). (4) Identical groups

\to

di, tri, tetra with comma-separated locants. (5) At a tie, lowest locant to the one

first alphabetically

🎯 Exam · Choosing the chain & ring rule

If two chains tie in length, pick the one with

more substituents

. A branched substituent is numbered from its own point of attachment (

= 1

). Saturated rings take the prefix

cyclo

, with the more-branched carbon getting the lower number.

⚠️ Watch out · Lowest-locant set, not first point

Compare the whole

set

of locants: 2,4-dimethyl... beats 3,5-... because the set

{2, 4}

is lower than

{3, 5}

at the first difference.

🚫 Examiner Trap · Examiner traps

(1) Parent

=

LONGEST continuous chain (containing the principal group). (2) Number for the lowest

set

of locants (compare at first difference):

{2, 4}

beats

{3, 5}

. (3) Cite substituents ALPHABETICALLY, ignoring di/tri prefixes (but iso/neo count). (4) Chain tie

\to

pick the one with MORE substituents.

IUPAC Nomenclature II — Functional Groups & Priority

Class	Group	Suffix
Carboxylic acid	$- COOH$	-oic acid
Ester	$- COOR$	-oate
Amide	$- CON H_{2}$	-amide
Nitrile	$- CN$	-nitrile
Aldehyde	$- CHO$	-al
Ketone	$> C = O$	-one
Alcohol	$- OH$	-ol
Amine	$- N H_{2}$	-amine

Principal functional group: In a polyfunctional molecule, the

senior

(highest-priority) group is named as the

suffix

and numbered for the lowest locant; every other group becomes a

prefix

Priority order (suffix goes to the highest)

- COOH > - S O_{3} H > - COOR > - COCl > - CON H_{2} > - CN > - CHO > > C = O > - OH > - N H_{2}

Then

> C = C <

and

- C \equiv C -

(shown by

-

ene/

-

yne).

★ Remember · Always-prefix groups

- R

(alkyl),

C_{6} H_{5} -

(phenyl), halogens (

- X

- N O_{2}

(nitro) and

- OR

(alkoxy) are

never

the principal group — they are always written as prefixes.

C_{8}

chain, OH at 3, Me at 6

6-methyloctan-3-ol

two ketones (C6)

hexane-2,4-dione

acid (suffix) + ketone (prefix)

5-oxohexanoic acid

🎯 Exam · Substituted benzene

Name as substituent-prefix

+

benzene; for two substituents use

ortho

(1,2),

meta

(1,3) or

para

(1,4). Many common names (toluene, aniline, phenol) are still accepted.

🚫 Examiner Trap · Examiner traps

(1) The

senior

functional group becomes the SUFFIX (lowest locant); all others are prefixes. (2) Priority:

-

COOH

> -

COOR

> - CON H_{2} > -

> -

CHO

>

=

> -

> - N H_{2}

. (3)

-

-

C_{6}

H_{5}

, halogens,

- N O_{2}

-

OR are

ALWAYS prefixes

(never the principal group). (4) Disubstituted benzene: ortho (1,2), meta (1,3), para (1,4).

Isomerism

Isomers: Different compounds with the

same molecular formula

but different arrangements of atoms, hence different properties. Two broad families:

structural

(different connectivity) and

stereo

(same connectivity, different 3-D arrangement).

Stereoisomers: cis/trans (geometrical) and a pair of enantiomers (optical).

Structural isomerism

▸ $Chain$ : different carbon skeleton — n-butane vs isobutane ( $C_{4} H_{10}$ ).
▸ $Position$ : group on a different carbon — propan-1-ol vs propan-2-ol.
▸ $Functional$ : different group — ethanol vs dimethyl ether ( $C_{2} H_{6} O$ ).
▸ $Metamerism$ : different alkyl groups around a hetero atom (diethyl ether vs methyl propyl ether).
▸ $Tautomerism$ : rapid interconversion, e.g. keto $⇌$ enol.

★ Remember · Geometrical (cis / trans)

Arises from

restricted rotation

about a

C = C

(or in rings).

cis

=

like groups on the same side,

trans

=

opposite sides — only when each doubly-bonded carbon carries two

different

groups.

🎯 Exam · Optical isomerism

chiral

molecule (e.g. a carbon with four different groups) is non-superimposable on its mirror image — the two

enantiomers

(d and l) rotate plane-polarised light in opposite directions.

⚠️ Watch out · Conformations are not isomers to 'separate'

Conformational

isomers (staggered vs eclipsed, from rotation about a C–C single bond) interconvert freely and cannot be isolated — unlike configurational stereoisomers.

🚫 Examiner Trap · Examiner traps

(1)

Metamerism

=

different alkyl groups around a heteroatom (diethyl ether vs methyl propyl ether). (2) cis/trans needs restricted rotation AND each C of the C

=

C carrying two DIFFERENT groups. (3) Optical isomers (enantiomers) need a chiral centre (4 different groups). (4)

Conformers

(staggered/eclipsed) interconvert freely — they CANNOT be isolated.

Electronic Effects

★ Remember · Inductive effect (±I) — permanent

permanent

polarisation of

σ

bonds toward an electronegative atom/group; it

weakens with distance

(

δ^{+} > δ δ^{+}

) and dies out after ~3 bonds.

-I

(electron-withdrawing:

- N O_{2}

- X

) vs

+I

(electron-donating: alkyl).

🎯 Exam · Electromeric effect (±E) — temporary

complete

transfer of a

π

-electron pair, happening

only while

an attacking reagent is present (e.g.

> C = C < + H^{+}

). It vanishes once the reagent leaves.

★ Remember · Resonance / mesomeric effect (±R)

Delocalisation of electrons over

π

bonds and adjacent lone pairs. The real molecule is a

resonance hybrid

of the canonical forms — lower in energy by the

resonance energy

(e.g. the two equivalent forms of

C H_{3} CO O^{-}

, or benzene).

🎯 Exam · Hyperconjugation ('no-bond resonance')

Delocalisation of

σ

(C–H) electrons of an

α

-carbon into an adjacent empty p or

π

orbital. More

α

C–H bonds

\Rightarrow

greater stabilisation —

(C H_{3})_{3} C +

has

nine

, so it is the most stable carbocation.

Permanent vs temporary

▸ $Permanent$ : inductive, resonance, hyperconjugation (built into the molecule).
▸ $Temporary$ : electromeric (only during attack by a reagent).
▸When inductive and electromeric oppose, the $electromeric effect wins$ .

🚫 Examiner Trap · Examiner traps

(1)

Inductive

(

\pm I

) is permanent, through

σ

bonds, dies out after ~3 bonds. (2)

Electromeric

(

\pm E

) is temporary — only while a reagent attacks (and it WINS if it opposes inductive). (3) Resonance gives a single hybrid, lower by the resonance energy (NOT flipping forms). (4)

Hyperconjugation

: more

α

C–H

\Rightarrow

more stable —

(C H_{3})_{3} C^{+}

has 9.

Reaction Mechanism & Intermediates

★ Remember · Two ways a bond breaks

Homolytic

(heat/light): one electron to each fragment

\to

free radicals

(half-headed fish-hook arrows).

Heterolytic

: the pair stays with one fragment

\to

carbocation

+

carbanion

(full curved arrow).

Nucleophiles & electrophiles: A

nucleophile

(Nu:) is electron-rich and

donates

a pair —

O H^{-}

C N^{-}

H_{2} O

N H_{3}

. An

electrophile

(

E^{+}

) is electron-deficient and

accepts

a pair —

H^{+}

, carbocations, the carbon of

> C = O

🎯 Exam · Stability of intermediates

Carbocations and free radicals:

3^{\circ} > 2^{\circ} > 1^{\circ} > C H_{3}

(stabilised by hyperconjugation and the

+ I

of alkyl groups).

Carbanions

follow the

reverse

order:

C H_{3} > 1^{\circ} > 2^{\circ} > 3^{\circ}

★ Remember · Carbocation shape

A carbocation carbon is

sp^{2}

hybridised and planar

with a sextet (empty p orbital) — which is why hyperconjugation from neighbouring C–H bonds can stabilise it.

Four reaction types

▸ $Substitution$ — one group replaces another.
▸ $Addition$ — reagent adds across a multiple bond.
▸ $Elimination$ — a small molecule is removed to form a multiple bond.
▸ $Rearrangement$ — atoms reorganise within the molecule.

🚫 Examiner Trap · Examiner traps

(1)

Homolytic

(heat/light)

\to

radicals (fish-hook arrows);

heterolytic

\to

carbocation

+

carbanion (curved arrow). (2) Nucleophile

=

electron-rich DONOR (OH

^{-}

); electrophile

=

electron-poor ACCEPTOR (H

^{+}

, C of C

=

O). (3) Carbocation/radical stability

3^{\circ} > 2^{\circ} > 1^{\circ} > C H_{3}

;

carbanion REVERSED

. (4) A carbocation is

s p^{2}

, planar, with an empty p orbital.

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This Some Basic Principles of Organic Chemistry formula sheet covers all the high-yield Chemistry formulas, definitions and theorems you need for JEE Main, across Tetravalency of carbon, Shapes of simple molecules, Hybridization (s and p), Classification of organic compounds based on functional groups, Compounds containing halogens, oxygen, nitrogen and sulphur — each shown with the key result and, where useful, a worked example.

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