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Schooling · Class 11 · Chemistry · Organic Chemistry – Some Basic Principles and Techniques · Chapter on a page

CBSE Class 11 · Chemistry · NCERT Chemistry Part II

Organic Chemistry – Some Basic Principles and Techniques: chapter on a page

A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).

About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.

Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain.

Mind map

Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.

Mind map of Organic Chemistry – Some Basic Principles and Techniques: Key ideas, Formulas and facts, Worked examples, Watch out forKey ideasTetravalency of carbonCatenationStructural representationFunctional groupsHomologous seriesIUPAC nomenclatureIsomerismFormulas and factsGeneral formula of alkanesGeneral formula of alkenesGeneral formula of alkynesDegree of unsaturation (DBE)Rf value in chromatographyBoiling-point trendElectronegativity order affecting…Worked examplesWriting the IUPAC nameCalculating degree of unsaturationChoosing a purification methodWatch out forWriting –OH at any position and…Confusing molecular formula with…Using common names such as acetone…Thinking chromatography always uses…Ignoring the inductive effect when…Organic Chemistry –Some BasicPrinciples andTechniques
The mind map as a list
  • Key ideas
    • Tetravalency of carbon
    • Catenation
    • Structural representation
    • Functional groups
    • Homologous series
    • IUPAC nomenclature
    • Isomerism
  • Formulas and facts
    • General formula of alkanes
    • General formula of alkenes
    • General formula of alkynes
    • Degree of unsaturation (DBE)
    • Rf value in chromatography
    • Boiling-point trend
    • Electronegativity order affecting…
  • Worked examples
    • Writing the IUPAC name
    • Calculating degree of unsaturation
    • Choosing a purification method
  • Watch out for
    • Writing –OH at any position and…
    • Confusing molecular formula with…
    • Using common names such as acetone…
    • Thinking chromatography always uses…
    • Ignoring the inductive effect when…

What this chapter is about

This chapter introduces you to the foundations of organic chemistry, the branch that studies carbon-containing compounds. Carbon forms more compounds than any other element because of its unique ability to bond with itself and other atoms in chains, rings and complex three-dimensional shapes. You will learn why carbon is special, how organic compounds are classified, and the rules for naming them systematically using IUPAC nomenclature.

Key ideas

  • Tetravalency of carbon: Carbon has four valence electrons and forms four covalent bonds, allowing it to create stable chains, branched structures and rings.
  • Catenation: Carbon atoms bond strongly with each other, forming long chains and closed rings; this property explains the vast number of organic compounds.
  • Structural representation: Organic molecules can be shown as complete structural formulas, condensed formulas (CH₃–CH₂–OH) or bond-line formulas where each vertex represents a carbon atom.
  • Functional groups: Atoms or groups of atoms that give characteristic chemical properties, such as –OH (alcohol), –CHO (aldehyde), –COOH (carboxylic acid), C=C (alkene) and –NH₂ (amine).
  • Homologous series: A family of compounds with the same functional group and general formula, differing by a –CH₂– unit, showing gradual change in physical properties.
  • IUPAC nomenclature: A systematic method for naming compounds using a root word (number of carbons), a suffix (functional group) and prefixes (substituents with their positions).
  • Isomerism: Compounds with the same molecular formula but different structural arrangements; chain isomers differ in carbon skeleton, position isomers differ in the location of a functional group.
  • Purification techniques: Distillation separates liquids by boiling-point differences; crystallisation purifies solids by dissolving and cooling; chromatography separates components based on differential adsorption or on differential partitioning between a stationary and a mobile phase.

Formulas and facts to remember

  • General formula of alkanes: CₙH₂ₙ₊₂ (saturated hydrocarbons with only single bonds).
  • General formula of alkenes: CₙH₂ₙ (one carbon–carbon double bond).
  • General formula of alkynes: CₙH₂ₙ₋₂ (one carbon–carbon triple bond).
  • Degree of unsaturation (DBE): (2C + 2 + N − H − X) / 2, where C = carbons, N = nitrogens, H = hydrogens, X = halogens; counts rings plus multiple bonds.
  • Rf value in chromatography: Rf = (distance moved by substance) / (distance moved by solvent front); a characteristic ratio used to identify compounds.
  • Boiling-point trend: In a homologous series, boiling point rises by roughly 20–30 °C for each added –CH₂– unit because of increasing molecular mass and surface area.
  • Electronegativity order affecting polarity: F > O > N > C; bonds to more electronegative atoms are polar and influence solubility and reactivity.
  • Inductive effect: Electron-withdrawing groups (–NO₂, –Cl) pull electron density through sigma bonds; electron-donating groups (–CH₃) push electron density; both affect acidity and basicity.

Common mistakes

  • Writing –OH at any position and forgetting to number from the end nearest the principal functional group → always number the chain so the principal group gets the lowest locant.
  • Confusing molecular formula with structural formula and assuming one molecular formula gives one compound → remember that isomers share the same molecular formula but have different structures.
  • Using common names such as acetone or acetic acid in IUPAC answers → use systematic names (propan-2-one, ethanoic acid).
  • Thinking chromatography always uses paper → chromatography includes thin-layer (TLC), column and gas chromatography, each suited to different mixtures.
  • Ignoring the inductive effect when comparing acidities → electron-withdrawing groups stabilise the conjugate base and increase acidity; electron-donating groups do the opposite.

Quick revision

  • Carbon's tetravalency and catenation explain the enormous variety of organic compounds.
  • IUPAC names follow the pattern: locant + prefix + root + suffix (e.g., 2-methylpropan-1-ol).
  • Functional groups determine chemical behaviour; the carbon skeleton determines physical properties.
  • Degree of unsaturation tells you how many rings or multiple bonds to look for.
  • Distillation separates by boiling point; crystallisation purifies solids; sublimation separates volatile solids; chromatography separates by differential adsorption or partition.
  • Rf value in chromatography is a ratio of distances and helps identify substances.