313_Chemistry_Eng_Lesson23.pdf). Content covers sections 23.1–23.6.Organic chemistry is the chemistry of carbon compounds (excluding simple oxides, carbonates, cyanides and carbides). Carbon’s unique catenation builds chains, rings and networks — fuels, foods, polymers, drugs and dyes. This lesson covers classification of hydrocarbons, IUPAC naming, bond fission and electronic effects, reaction types, isomerism (including R/S and D/L), and qualitative/quantitative organic analysis.
Open-chain (aliphatic): saturated alkanes (C–C single) and unsaturated alkenes (C=C) / alkynes (C≡C).
Closed-chain (cyclic): homocyclic (only C in ring) — alicyclic (cycloalkanes etc.) or aromatic (benzene and derivatives); heterocyclic (N, O, S in ring).
Word root gives carbon count (meth–dec); suffix gives saturation: -ane, -ene, -yne. Branched compounds use alkyl prefixes (methyl, ethyl, isopropyl, tert-butyl…).
Key rules: (1) longest continuous chain including multiple bond; if tie, more substituents; (2) lowest numbers for unsaturation then substituents; (3) alphabetical prefixes (ignore di/tri); (4) multiple identical groups di/tri/tetra. Cyclic: cyclo- + hydrocarbon name; number substituents for lowest set.
Functional groups (halo, hydroxy, etc.) get prefixes or priority suffixes in later lessons; L23 focuses on hydrocarbon parents and general organic principles.
Homolytic fission: equal electron share → free radicals (·CH₃). Initiated by heat/light. Heterolytic fission: unequal share → carbocation (C⁺) + carbanion (C⁻).
Electrophiles (E⁺): electron-deficient — H⁺, NO₂⁺, Br⁺, BF₃. Attack high electron density. Nucleophiles (Nu): electron-rich — OH⁻, CN⁻, NH₃, H₂O. Attack δ⁺ carbon.
Inductive effect: permanent polarisation along σ chain. −I (withdrawing): NO₂, CN, halogens… +I (releasing): alkyl groups (tert-butyl strongest). Explains acid strength trends.
Electromeric: temporary complete transfer of π pair under reagent attack (C=O, C=C).
Resonance: molecule as hybrid of canonical forms (benzene equal C–C bonds 139 pm; carboxylate; nitro).
Hyperconjugation: σ–π conjugation (“no-bond resonance”), e.g. propene methyl hydrogens with C=C — stabilises alkenes/carbocations.
Steric hindrance: bulky groups block reagent approach (Hofmann/Meyer).
Substitution: replace atom/group. Aliphatic: nucleophilic (R–X + OH⁻ → R–OH). Aromatic: electrophilic (benzene + HNO₃/H₂SO₄ → nitrobenzene).
Addition: to C=C/C≡C (π bond opens). Br₂ decolourises; H₂/Ni, HX add. Alkynes take two moles of H₂ to alkanes.
Elimination: remove small molecule from adjacent carbons → double bond (ethanol + H₂SO₄, 403 K → ethene + H₂O).
Rearrangement: skeleton change (1-chlorobutane + AlCl₃ → 2-chlorobutane).
Structural: chain (n-butane / isobutane); position (propan-1-ol / propan-2-ol); functional (ethanol / methoxymethane); metamerism (1-methoxypropane / ethoxyethane).
Stereo: geometrical cis–trans (restricted rotation about C=C); optical when chiral carbon (four different groups) → enantiomers, d(+) / l(−), racemic (±) inactive.
Absolute configuration: D/L from Fischer projection (OH right = D for glyceraldehyde reference). R/S by Cahn–Ingold–Prelog priorities: lowest priority away; 1→2→3 clockwise = R, anticlockwise = S. Optical rotation (+/−) is independent of R/S or D/L labels.
C and H: heat with CuO → CO₂ (lime water milky) and H₂O (anhydrous CuSO₄ → blue).
Lassaigne’s test: fuse with Na → NaCN, Na₂S, NaX extracted in water. N: FeSO₄ + conc. H₂SO₄ → Prussian blue. N+S: blood-red Fe(CNS)₃. S: sodium nitroprusside violet or PbS black. Halogens: AgNO₃ after HNO₃ — white AgCl, pale yellow AgBr, yellow AgI (solubility in NH₄OH differs). Not given by NH₂NH₂, NH₂OH, or diazonium salts (no stable CN⁻).
Liebig (C, H): burn with CuO; absorb CO₂ in KOH, H₂O in CaCl₂.
Carius (halogens, S): fuming HNO₃ + AgNO₃ → AgX; S → BaSO₄. %Cl = 35.5/143.5 × (m_AgCl/m)×100; %S = 32/233 × (m_BaSO₄/m)×100.
Phosphorus: → H₃PO₄ → ammonium phosphomolybdate or Mg₂P₂O₇.
Nitrogen: Dumas (CuO, collect N₂ over KOH) or Kjeldahl (digest to (NH₄)₂SO₄, liberate NH₃, titrate).
This chapter is the grammar of organic chemistry. Exam favourites: IUPAC naming and structure writing; homo/hetero fission; E⁺/Nu lists; −I/+I order; reaction type identification; isomer classification; R/S or cis–trans assignment; Lassaigne observations; Liebig/Carius percentage calculations.
Leads into L24 hydrocarbons and later functional-group lessons. Master naming + mechanism vocabulary + analysis formulas and every later organic chapter becomes easier.
Intext-style drills: name branched alkenes; classify E⁺/Nu; identify −I groups; product of CH₂=CH₂ + HBr; type of isomerism for C₂H₆O pairs; cis–trans for CHF=CHF; R/S sketch; Lassaigne colour codes; compute %C from CO₂ mass. Liebig numbers: %C = (12/44)×(m_CO₂/m)×100; %H = (2/18)×(m_H₂O/m)×100. Carius: %Cl = 35.5/143.5 × (m_AgCl/m)×100; %S = 32/233 × (m_BaSO₄/m)×100.
Most exam-important points from this chapter:
Aliphatic / cyclic / aromatic / hetero. IUPAC: longest chain, lowest locants, prefixes, -ane/-ene/-yne.
Homo → radicals; hetero → ions. E⁺ attacks e⁻-rich sites; Nu attacks δ⁺ carbon.
−I/+I permanent; electromeric temporary; resonance & hyperconjugation delocalise; steric blocks approach.
Sub / add / elim / rearrange. Structural vs stereo; cis–trans; optical; R/S and D/L ≠ rotation sign.
CuO detects C/H. Lassaigne for N/S/X. Liebig %C/%H; Carius X/S; Dumas/Kjeldahl N.
Extracted from NIOS Chemistry (313) board exam papers in your PDF. Chapter L23 — Nomenclature and General Principles only. Use Model Answer for marking points; Explanation for concept clarity.
8 question(s) · Sources: 313/MAY/205A, 313/MAY/205B, 313/MAY/205C, 313/TUS/105A
PYQ1. The pair of complexes which shows linkage isomerism is — (A) [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br (B) [Co(NH3)5SCN]2+ and [Co(NH3)5NCS]2+ (C) [Co(NH3)6]3+ and [Cr(C2O4)3]3– (D) [Cr(H2O)5Cl]Cl2
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205A · Q11.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ2. The IUPAC name of CH3CH2SH is — (A) methanethiol (B) ethanethiol (C) ethyl sulphur hydride (D) ethane CH3CH2SH
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205A · Q12.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ3. Match the items in Column—I with Column—II : Column—I Column—II Nucleophile Electrophile CH CH Carbocation (iii) Free radical
Model Answer
Answer using key concepts from L23 (definitions, equations, and one example where useful). Stay within the suggested word range for a 2-mark NIOS question.
Explanation
Cross-check with L23 notes. Structure: definition/law → working → conclusion. Partial marks for correct equations even if explanation is short.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205A · Q24 · 2 mark(s) · L23.
PYQ4. The pair of complexes which shows linkage isomerism is — (A) [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br (B) [Co(NH3)5SCN]2+ and [Co(NH3)5NCS]2+ (C) [Co(NH3)6]3+ and [Cr(C2O4)3]3– (D) [Cr(H2O)5Cl]Cl2
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205B · Q4.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ5. The IUPAC name of CH3CH2SH is — (A) methanethiol (B) ethanethiol (C) ethyl sulphur hydride (D) ethane CH3CH2SH
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205B · Q15.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ6. The IUPAC name of CH3CH2SH is — (A) methanethiol (B) ethanethiol (C) ethyl sulphur hydride (D) ethane CH3CH2SH
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205C · Q4.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ7. The pair of complexes which shows linkage isomerism is — (A) [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br (B) [Co(NH3)5SCN]2+ and [Co(NH3)5NCS]2+ (C) [Co(NH3)6]3+ and [Cr(C2O4)3]3– (D) [Cr(H2O)5Cl]Cl2
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/MAY/205C · Q14.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ8. The temporary electron displacement which takes place in compounds containing multiple covalent bonds developing +ve and –ve charges within the molecule is known as — (A) resonance (B) electromeric effect (C) inductive effect (D) hyperconjugation
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L23. Recall the core definition or formula from notes, then match it to one option. Paper: 313/TUS/105A · Q8.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
Six problems spanning this chapter’s NIOS syllabus. Every question is built from the notes and formula sheet: solve with equations first, then read the formal textbook-style write-up, the easy explanation, and the topic in depth (formulas, meaning, exam tips). If the question says draw, a labelled pencil sketch is provided. Explanations open by default.
State the correct order of steps in IUPAC naming of a simple organic compound.
Final answer: Longest chain → number → substituents + parent + suffix
IUPAC provides unique systematic names.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Find the main chain, number it smartly, then stick prefixes and ending.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Functional group priority decides suffix.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What are structural isomers? Example C₄H₁₀.
Final answer: n-butane & 2-methylpropane
Structural isomerism includes chain, position, functional isomers.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Same atoms, different wiring diagram.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Stereoisomerism is different arrangement in space.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
State two features of a homologous series.
Final answer: CH₂ difference; same functional group
Homologues prepared by similar methods.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Like a family: methanol, ethanol, propanol…
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Boiling points rise with molar mass.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What is the +I effect? Give one group that shows +I.
Final answer: Alkyl +I
Inductive effect operates through σ bonds.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Alkyl groups push electrons slightly toward the chain.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Affects acid strength of carboxylic acids.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Why is benzene more stable than a hypothetical cyclohexatriene?
Final answer: Resonance / aromatic stabilisation
Resonance hybrid lower in energy than contributing structures.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Electrons are smeared over the ring, not stuck in three double bonds.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Equal C–C bond lengths in benzene.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
State the principle of chromatography briefly.
Final answer: Different affinities for stationary vs mobile phase
Physical method of separation based on relative migration.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Components race differently on paper/column.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Used for dyes, amino acids, purity checks.
Linked to chapter notes (L23). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.