Organic Chemistry: Some Basic Principles and Techniques is Unit 8 of NCERT Class 11 Chemistry Part II and maps to Units 13 and 14 of both the NEET UG 2026 and JEE Main 2026 syllabi. These notes cover hybridisation, IUPAC naming, isomerism, reaction intermediates, electronic effects, purification, and qualitative and quantitative analysis, with a free PDF.
Organic Chemistry: Some Basic Principles and Techniques Notes
Section-wise key points from NCERT Unit 8, rule and formula tables, high-yield facts and common mistakes for NEET and JEE Main 2027 revision.
Organic Chemistry: Some Basic Principles and Techniques at a Glance
| Item | Details |
|---|---|
| Exams that cover it | NEET UG (NMC syllabus 2026) and JEE Main (NTA syllabus 2026): Unit 13, Purification and Characterisation of Organic Compounds, and Unit 14, Some Basic Principles of Organic Chemistry, in both |
| Syllabus section | Organic Chemistry |
| NCERT textbook | Chemistry Part II, Class 11, Unit 8 (rationalised book) |
| Linked units | Hydrocarbons (NCERT Unit 9) applies these ideas; detection of N, S and halogens also appears in Unit 20, Principles Related to Practical Chemistry |
| Syllabus topics | Purification: crystallisation, sublimation, distillation, differential extraction, chromatography; detection of N, S, P and halogens; estimation of C, H, N, halogens, S, P; empirical and molecular formula problems; tetravalency of carbon and sp, sp², sp³ shapes; functional-group classification; homologous series; structural and stereoisomerism; trivial and IUPAC nomenclature; homolytic and heterolytic fission; free radicals, carbocations, carbanions and their stability; electrophiles and nucleophiles; inductive, electromeric, resonance and hyperconjugation effects; substitution, addition, elimination and rearrangement |
| Official chapter | NCERT Unit 8 |
| Notes PDF | View PDF |
The topic list follows the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and the JEE Main 2026 syllabus published by NTA. These stay the reference until the 2027 syllabi are out. Full lists: NEET syllabus and JEE Main syllabus.
How did organic chemistry begin?
- Around 1780 chemists began to separate organic compounds (from plants and animals) from inorganic compounds (from minerals).
- Berzelius, a Swedish chemist, proposed that a ‘vital force’ was needed to make organic compounds.
- F. Wöhler disproved this in 1828 by making urea (NH₂CONH₂) from ammonium cyanate (NH₄CNO), an inorganic compound.
- Kolbe synthesised acetic acid (1845) and Berthelot synthesised methane (1856), confirming that organic compounds can be made from inorganic sources.
- Carbon forms so many compounds because of catenation and its tetravalence.
Tetravalence of Carbon: Hybridisation and Shapes
Carbon uses sp³, sp² or sp hybrid orbitals. More s character means a shorter, stronger bond and a more electronegative carbon.
| Hybridisation | s character | Shape | Example |
|---|---|---|---|
| sp³ | 25% | Tetrahedral | Methane CH₄, CH₃F |
| sp² | 33% | Trigonal planar | Ethene C₂H₄, H₂C=O |
| sp | 50% | Linear | Ethyne C₂H₂, HC≡N |
- A π bond needs parallel p orbitals on adjacent atoms, so all six atoms of ethene lie in one plane and rotation about C=C is restricted.
- π electrons lie above and below the plane of the bonded atoms, so they are easily available to attacking reagents; π bonds are the most reactive centres in molecules with multiple bonds.
- Counting example from NCERT: CH₂=C=CHCH₃ has 9 σ and 2 π bonds; in CH₃CH=CHCN the carbons are sp³, sp², sp² and sp.
Structural Representations and Molecular Models
- Complete structural formula: every bond shown as a dash (single, double or triple).
- Condensed formula: dashes omitted and identical groups grouped, e.g. CH₃(CH₂)₆CH₃.
- Bond-line formula: carbon and hydrogen not written; zig-zag lines show C-C bonds, line ends are methyl groups, and heteroatoms (O, N, Cl) are written.
- Wedge-dash (3-D) formula: solid wedge points towards the observer, dashed wedge away; normal lines lie in the plane of the paper.
| Molecular model | What it shows |
|---|---|
| Framework model | Only the bonds, not the atoms; emphasises bonding pattern |
| Ball-and-stick model | Atoms as balls and bonds as sticks (springs for C=C in the ball-and-spring version) |
| Space-filling model | Relative size of each atom based on van der Waals radius; bonds not shown |
Classification of Organic Compounds
| Class | Description | NCERT examples |
|---|---|---|
| Acyclic (open chain, aliphatic) | Straight or branched chains | Ethane, isobutane, acetaldehyde, acetic acid |
| Alicyclic | Carbon ring (homocyclic) or ring with another atom (heterocyclic); properties like aliphatic compounds | Cyclopropane, cyclohexane, cyclohexene; tetrahydrofuran (heterocyclic) |
| Benzenoid aromatic | Benzene and related rings | Benzene, aniline, naphthalene |
| Non-benzenoid aromatic | Aromatic without a benzene ring | Tropone |
| Heterocyclic aromatic | Aromatic ring containing a heteroatom | Furan, thiophene, pyridine |
- Functional group: an atom or group responsible for the characteristic chemical properties, e.g. -OH, -CHO, -COOH.
- Homologous series: compounds with the same functional group and a general formula; successive members differ by a -CH₂ unit.
IUPAC Nomenclature: Key Rules
- Pick the longest carbon chain (with the functional group, if any) as the parent chain.
- Number it so that branches (or the principal functional group) get the lowest possible locants. Example: 6-ethyl-2-methylnonane, not 4-ethyl-8-methylnonane.
- List substituents in alphabetical order; di, tri, tetra are ignored when alphabetising.
- If substituents sit in equivalent positions, the one first in alphabetical order gets the lower number: 3-ethyl-6-methyloctane.
- iso- and neo- count as part of the alkyl name for alphabetising; sec- and tert- do not.
- With two chains of equal length, choose the one with more side chains.
- In a branched substituent, the carbon attached to the parent chain is numbered 1 and the name goes in brackets, e.g. 5-(2-ethylbutyl)-3,3-dimethyldecane.
- Rings take the prefix cyclo-, e.g. 3-ethyl-1,1-dimethylcyclohexane.
- With more than one double or triple bond, the -ne ending of the alkane changes: CH₂=CH-CH=CH₂ is buta-1,3-diene; with two -OH groups the full alkane name stays: ethane-1,2-diol.
Order of Priority of Functional Groups
-COOH > -SO₃H > -COOR > -COCl > -CONH₂ > -CN > -CHO > >C=O > -OH > -NH₂ > >C=C< > -C≡C-. The groups -R, C₆H₅-, halogens, -NO₂ and alkoxy (-OR) are always written as prefixes. So HOCH₂(CH₂)₃CH₂COCH₃ is 7-hydroxyheptan-2-one, and BrCH₂CH=CH₂ is 3-bromoprop-1-ene.
| Class | Prefix | Suffix | Example |
|---|---|---|---|
| Alcohol (-OH) | hydroxy- | -ol | Butan-2-ol |
| Aldehyde (-CHO) | formyl or oxo | -al | Butanal |
| Ketone (>C=O) | oxo- | -one | Butan-2-one |
| Carboxylic acid (-COOH) | carboxy | -oic acid | Butanoic acid |
| Ester (-COOR) | alkoxycarbonyl | -oate | Methyl propanoate |
| Acyl halide (-COX) | halocarbonyl | -oyl halide | Butanoyl chloride |
| Amide (-CONH₂) | carbamoyl | -amide | Butanamide |
| Nitrile (-CN) | cyano | -nitrile | Pentanenitrile |
| Amine (-NH₂) | amino- | -amine | Butan-2-amine |
| Ether (R-O-R) | alkoxy- | none | Ethoxyethane |
| Halide, nitro | halo-, nitro- | none | 1-Bromobutane, 1-nitrobutane |
Substituted Benzene Compounds
- Number the ring so substituents get the lowest locants: 1,3-dibromobenzene, not 1,5-dibromobenzene.
- ortho (o-), meta (m-) and para (p-) mean 1,2-, 1,3- and 1,4-; they cannot be used for three or more substituents.
- With a base compound such as anisole or aniline, its substituent is C-1: 2-chloro-4-methylanisole, 4-ethyl-2-methylaniline.
- When a benzene ring is attached to an alkane with a functional group, it is named as the substituent phenyl (C₆H₅-, Ph).
Isomerism
Isomers have the same molecular formula but different properties. NCERT divides isomerism into structural isomerism and stereoisomerism.
| Type | How the isomers differ | NCERT example |
|---|---|---|
| Chain isomerism | Different carbon skeletons | C₅H₁₂: pentane, isopentane (2-methylbutane), neopentane (2,2-dimethylpropane) |
| Position isomerism | Position of a substituent or functional group | C₃H₈O: propan-1-ol and propan-2-ol |
| Functional group isomerism | Different functional groups | C₃H₆O: propanal and propanone |
| Metamerism | Different alkyl chains on either side of the functional group | C₄H₁₀O: methoxypropane and ethoxyethane |
| Stereoisomerism | Same constitution and bond sequence, different arrangement in space | Divided into geometrical and optical isomerism |
Bond Fission and Reactive Intermediates
Heterolytic cleavage leaves the shared pair on one fragment and gives ions (polar reactions). Homolytic cleavage sends one electron to each fragment and gives free radicals (free radical or non-polar reactions), shown with a half-headed fish-hook arrow.
| Intermediate | Formed by | Hybridisation and shape | Stability order |
|---|---|---|---|
| Carbocation (earlier carbonium ion) | Heterolysis; carbon has a sextet and + charge | sp², trigonal planar; empty p orbital | (CH₃)₃C⁺ > (CH₃)₂CH⁺ > CH₃CH₂⁺ > CH₃⁺ |
| Carbanion | Heterolysis; carbon keeps the electron pair, − charge | Generally sp³, distorted tetrahedral | Unstable and reactive |
| Free radical | Homolysis; one unpaired electron | Neutral species | Tertiary > secondary > primary > methyl |
- Alkyl groups stabilise carbocations through inductive and hyperconjugation effects.
- Carbocations are classed as primary, secondary or tertiary by the number of carbons attached to the positive carbon.
Substrate, Reagent, Nucleophiles and Electrophiles
- Substrate: the reactant that supplies carbon to the new bond; the other reactant is the reagent. If both supply carbon, the choice is arbitrary.
- Nucleophile (Nu:, nucleus seeking): brings an electron pair to the reactive site. Examples: HO⁻, NC⁻, carbanions, and neutral H₂O, R₃N, R₂NH with lone pairs.
- Electrophile (E⁺, electron seeking): takes an electron pair. Examples: carbocations, BF₃, and neutral molecules with carbonyl groups or alkyl halides, where carbon carries a partial positive charge.
- In CH₃CH=O, CH₃C≡N and CH₃I, the carbon bonded to O, N or I is the electrophilic centre.
- Curved arrows show movement of an electron pair from where it starts to where it goes; a fish-hook shows a single electron.
Electronic Displacement Effects
Inductive and resonance effects are permanent polarisations in the ground state; the electromeric effect is temporary and appears only when a reagent attacks. Hyperconjugation is a permanent stabilising interaction.
| Effect | What happens | Key points |
|---|---|---|
| Inductive effect | A polar σ bond polarises adjacent σ bonds | Falls rapidly along the chain and is vanishingly small after three bonds. Electron-withdrawing: halogens, -NO₂, -CN, -COOH, -COOR, -OAr. Electron-donating: alkyl groups such as -CH₃, -C₂H₅ |
| Resonance (mesomeric) effect | Polarity from interaction of two π bonds, or a π bond and an adjacent lone pair, in a conjugated system | +R: halogen, -OH, -OR, -OCOR, -NH₂, -NHR, -NR₂, -NHCOR. -R: -COOH, -CHO, >C=O, -CN, -NO₂. Transmitted through the chain |
| Electromeric effect (E) | Complete transfer of a shared π pair to one atom of a multiple bond on demand of an attacking reagent | +E: electrons move to the atom the reagent attaches to; -E: to the other atom. Annulled when the reagent is removed. Predominates over the inductive effect when they oppose |
| Hyperconjugation | Delocalisation of σ electrons of a C-H bond into an adjacent unsaturated system or empty p orbital | Also called no-bond resonance. Explains carbocation stability: (CH₃)₃C⁺ has nine C-H bonds for hyperconjugation; CH₃⁺ has none that can overlap. Also seen in alkenes and alkylarenes |
Resonance Structures
- Benzene has a uniform C-C bond length of 139 pm, between C-C (154 pm) and C=C (134 pm), so it is a resonance hybrid of two structures. Nitromethane’s two N-O bonds are also equal.
- Canonical (contributing) structures are hypothetical; the hybrid is lower in energy than any of them. The difference from the most stable structure is the resonance energy.
- Resonance structures keep the same positions of nuclei and the same number of unpaired electrons.
- More stable contributors have more covalent bonds, octets on all atoms (duplet for H), less charge separation, negative charge on the more electronegative atom and more charge dispersal.
Types of Organic Reactions
NCERT lists four types: substitution, addition, elimination and rearrangement. They are studied in detail in Hydrocarbons and Class 12 units.
Methods of Purification of Organic Compounds
Purity is finally checked by melting or boiling point: most pure compounds have sharp values. Modern checks use chromatographic and spectroscopic techniques.
| Method | Used for | NCERT example or key point |
|---|---|---|
| Sublimation | Sublimable solid from non-sublimable impurities | Solid changes directly to vapour on heating |
| Crystallisation | Purifying solids by solubility difference | Compound sparingly soluble cold, appreciably soluble hot; coloured impurities removed with activated charcoal; filtrate is the mother liquor |
| Simple distillation | Volatile liquid from non-volatile impurities, or liquids with large b.p. difference | Chloroform (b.p. 334 K) and aniline (b.p. 457 K) |
| Fractional distillation | Liquids with close boiling points | Fractionating column; each vaporisation-condensation unit is a theoretical plate; crude oil fractions |
| Distillation under reduced pressure | High-boiling liquids or those that decompose at or below their b.p. | Glycerol from spent-lye in the soap industry |
| Steam distillation | Steam-volatile liquids immiscible with water | Mixture boils when p(organic) + p(water) = atmospheric pressure, i.e. below 373 K; aniline from aniline-water mixture |
| Differential extraction | Organic compound in an aqueous medium | Shaken with an immiscible organic solvent in a separatory funnel; continuous extraction if the compound is less soluble |
| Chromatography | Separating mixtures, purifying and testing purity | Name from Greek chroma (colour); mixture on a stationary phase, carried by a mobile phase |
Types of Chromatography
| Type | Principle | Details |
|---|---|---|
| Column chromatography | Adsorption | Adsorbent (silica gel or alumina) in a glass column; most strongly adsorbed substances stay near the top; liquid eluant flows down |
| Thin layer chromatography (TLC) | Adsorption | About 0.2 mm adsorbent layer on a glass plate (chromaplate); Rf = distance moved by substance ÷ distance moved by solvent, both from the base line |
| Paper chromatography | Partition | Water trapped in chromatography paper is the stationary phase; the solvent (mobile phase) rises by capillary action |
Colourless spots are seen under ultraviolet light, as brown spots in an iodine jar, or with a spray reagent (ninhydrin for amino acids).
Qualitative Analysis: Detecting Elements
- Carbon and hydrogen: heat with copper(II) oxide. CO₂ turns lime water milky; water turns anhydrous (white) copper sulphate blue.
- Lassaigne’s test: fuse the compound with sodium metal to convert N, S and halogens into NaCN, Na₂S and NaX, then boil with distilled water to get the sodium fusion extract.
| Element | Test | Positive result |
|---|---|---|
| Nitrogen | Boil sodium fusion extract with FeSO₄, then acidify with conc. H₂SO₄ | Prussian blue, Fe₄[Fe(CN)₆]₃·xH₂O |
| Sulphur | (a) Acidify with acetic acid, add lead acetate; (b) add sodium nitroprusside | (a) Black PbS; (b) violet colour |
| Nitrogen and sulphur together | Forms NaSCN; test with Fe³⁺ | Blood red [Fe(SCN)]²⁺, no Prussian blue (no free CN⁻). Excess sodium splits NaSCN into NaCN and Na₂S |
| Halogens | Acidify with HNO₃, add AgNO₃ | Cl: white ppt soluble in NH₄OH; Br: yellowish ppt sparingly soluble; I: yellow ppt insoluble |
| Phosphorus | Heat compound with Na₂O₂, boil with HNO₃, add ammonium molybdate | Yellow colour or precipitate of ammonium phosphomolybdate |
If N or S is present, boil the extract with concentrated HNO₃ before the halogen test, so cyanide and sulphide do not interfere with AgNO₃.
Quantitative Analysis: Formulas for Each Element
Here m is the mass of the organic compound and m₁, m₂ the masses of the products weighed.
| Element | Method | Percentage formula |
|---|---|---|
| Carbon | Burn with O₂ and CuO; CO₂ absorbed in KOH | %C = 12 × m₂ × 100 / (44 × m), m₂ = mass of CO₂ |
| Hydrogen | Same experiment; water absorbed in anhydrous CaCl₂ | %H = 2 × m₁ × 100 / (18 × m), m₁ = mass of H₂O |
| Nitrogen | Dumas: heat with CuO in CO₂; N₂ collected over KOH | %N = 28 × V × 100 / (22400 × m), V = volume of N₂ at STP (mL); pressure corrected for aqueous tension |
| Nitrogen | Kjeldahl: digest with conc. H₂SO₄ to (NH₄)₂SO₄, liberate NH₃ with NaOH, absorb in standard acid | %N = 1.4 × M × 2(V − V₁/2) / m |
| Halogen | Carius: heat with fuming HNO₃ and AgNO₃ | %X = atomic mass of X × m₁ × 100 / (molecular mass of AgX × m) |
| Sulphur | Carius tube with Na₂O₂ or fuming HNO₃; precipitate as BaSO₄ | %S = 32 × m₁ × 100 / (233 × m) |
| Phosphorus | Fuming HNO₃; precipitate as ammonium phosphomolybdate (1877 g/mol) or Mg₂P₂O₇ (222 u) | %P = 31 × m₁ × 100 / (1877 × m), or 62 × m₁ × 100 / (222 × m) |
| Oxygen | Usually by difference; directly via coke to CO, then I₂O₅ | %O = 32 × m₁ × 100 / (88 × m), m₁ = mass of CO₂ |
- Kjeldahl’s method does not work for nitrogen in nitro and azo groups or in a ring (e.g. pyridine).
- Today C, H and N are found with a CHN elemental analyser using only 1 to 3 mg of substance.
- These percentages feed into empirical and molecular formula calculations, which are part of the syllabus.
Most-asked Facts for NEET and JEE Main: Organic Chemistry Basic Principles
Revise these one-line facts from the NCERT unit just before the exam.
- Wöhler (1828) made urea from ammonium cyanate and ended the vital force theory.
- s character: sp 50%, sp² 33%, sp³ 25%; higher s character means a more electronegative carbon.
- Functional group priority starts -COOH > -SO₃H > -COOR > -COCl > -CONH₂ > -CN > -CHO.
- Halogens, -NO₂, -OR and -R are always prefixes.
- iso- and neo- count in alphabetising; sec- and tert- do not.
- Propanal and propanone are functional group isomers; methoxypropane and ethoxyethane are metamers.
- Carbocation: sp², trigonal planar; carbanion: generally sp³, distorted tetrahedral.
- Carbocation and free radical stability: 3° > 2° > 1° > methyl.
- Inductive effect dies out after about three bonds.
- Electromeric effect is temporary and beats the inductive effect when they oppose.
- Hyperconjugation is no-bond resonance; (CH₃)₃C⁺ has nine hyperconjugable C-H bonds.
- Benzene C-C bond length is 139 pm (single 154 pm, double 134 pm).
- Steam distillation: the mixture boils below 373 K; aniline is purified this way.
- Glycerol is recovered from spent-lye by distillation under reduced pressure.
- Paper chromatography is partition chromatography; TLC and column are adsorption.
- Lassaigne’s test: Prussian blue for N, blood red for N and S together.
- AgCl is soluble in NH₄OH, AgBr sparingly soluble, AgI insoluble.
- Kjeldahl’s method fails for nitro, azo and ring nitrogen (pyridine).
Common Mistakes to Avoid
Watch for these mix-ups when you answer questions on this unit.
- Making the carbanion planar. NCERT gives it sp³ hybridisation and a distorted tetrahedral shape; the carbocation is the planar one.
- Giving the methyl cation hyperconjugative stability. Its C-H bonds lie in the plane perpendicular to the empty p orbital, so they cannot overlap with it.
- Treating the electromeric effect as permanent. It appears only while an attacking reagent is present.
- Using di-, tri- or sec-/tert- when alphabetising substituents.
- Choosing the parent chain without the principal functional group, or numbering from the wrong end.
- Naming a keto-alcohol as an -ol. Ketone outranks alcohol, so it is a hydroxy…-one (e.g. 7-hydroxyheptan-2-one).
- Applying Kjeldahl’s method to nitrobenzene, azo compounds or pyridine.
- Forgetting to boil the sodium fusion extract with conc. HNO₃ before the AgNO₃ test when N or S is present.
- Calling paper chromatography adsorption chromatography. Water held in the paper is a stationary liquid phase, so it is partition.
- Thinking resonance structures are real forms that interconvert. They are hypothetical; only the hybrid exists.
Organic Chemistry Basic Principles Notes PDF and Related Pages
Download the AglaSem notes for Organic Chemistry: Some Basic Principles and Techniques (key notes and important questions with answers) free: View PDF
- All chapters: Chemistry notes for NEET and JEE Main
- Full topic lists: NEET syllabus and JEE Main syllabus
- Practice: NEET question papers and JEE Main question papers
- Source text: NCERT Unit 8 (NCERT, Class 11 Chemistry Part II)
Chemistry Notes for NEET and JEE Main: All Chapters
- Some Basic Concepts of Chemistry
- Structure of Atom
- Chemical Kinetics
- Equilibrium
- Organic Chemistry: Some Basic Principles and Techniques
- Electrochemistry
- Amines
- Solutions
- Thermodynamics
- Coordination Compounds
- Haloalkanes and Haloarenes
- p-Block Elements
- Alcohols, Phenols and Ethers
- Hydrocarbons
- Aldehydes, Ketones and Carboxylic Acids
All chapters with key points and notes PDFs are on the Chemistry notes for NEET and JEE Main page.
Organic Chemistry: Some Basic Principles and Techniques Notes FAQs
Which NCERT chapter is Organic Chemistry: Some Basic Principles and Techniques?
It is Unit 8 of the NCERT Class 11 Chemistry textbook, Part II, between Redox Reactions (Unit 7) and Hydrocarbons (Unit 9). Students often call it GOC (general organic chemistry).
Is this chapter in the NEET 2027 and JEE Main 2027 syllabus?
Yes. Its topics form Unit 13 (Purification and Characterisation of Organic Compounds) and Unit 14 (Some Basic Principles of Organic Chemistry) in both the NEET UG 2026 syllabus from NMC and the JEE Main 2026 syllabus from NTA. The 2027 syllabi are not out yet.
Why is a tertiary carbocation more stable than a primary one?
Alkyl groups release electrons through the inductive effect and through hyperconjugation, which spreads the positive charge. (CH₃)₃C⁺ has nine C-H bonds that can hyperconjugate, so the order is tertiary > secondary > primary > methyl.
What is the difference between Dumas and Kjeldahl methods?
Dumas heats the compound with CuO in CO₂ and measures the volume of N₂ gas. Kjeldahl converts nitrogen to ammonium sulphate with conc. H₂SO₄ and measures the ammonia released. Kjeldahl does not work for nitro, azo or ring nitrogen.
Are these notes enough for GOC questions?
No. Read NCERT Unit 8 fully first, including the solved problems on naming, intermediates and percentage composition, then use these notes and the PDF for quick revision and practise previous year questions.