Some Basic Principles of Organic Chemistry Formula Sheet — NEET Chemistry

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

Syllabus — topics coveredNCERT · 6 sub-topics

Tetravalency of carbon; shapes of organic molecules; hybridization
Classification and IUPAC nomenclature of organic compounds
Isomerism — structural and stereoisomerism
Covalent bond fission; free radicals, carbocations, carbanions; electrophiles and nucleophiles
Electronic displacement effects — inductive, electromeric, resonance and hyperconjugation
Common types of organic reactions — substitution, addition, elimination, 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 facts you need for NEET, across Tetravalency of carbon; shapes of organic molecules; hybridization, Classification and IUPAC nomenclature of organic compounds, Isomerism — structural and stereoisomerism, Covalent bond fission; free radicals, carbocations, carbanions; electrophiles and nucleophiles, Electronic displacement effects — inductive, electromeric, resonance and hyperconjugation — each shown with the key result and, where useful, a worked example.

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