Unit 13 — Organic Chemistry
Fundamental Principles of Organic Chemistry
Class 11 Chemistry
Fundamental Principles of Organic Chemistry
IUPAC Nomenclature • Qualitative Analysis • Reaction Mechanism • Electronic Effects • Isomerism
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Current NEB/CDC scope: Unit 13 – Fundamental Principles of Organic Chemistry carries 10 teaching hours. It covers IUPAC nomenclature of compounds with parent chains up to six carbons; qualitative detection of N, S and halogens by Lassaigne’s test; structural, geometrical and optical isomerism; and preliminary reaction mechanism including bond fission, electrophiles, nucleophiles, free radicals, inductive effect, resonance effect and steric hindrance.
What the 33-page source actually contains: pp. 1–15 develop organic-compound classification, common/IUPAC nomenclature, naming rules, functional groups and homologous series; pp. 16–18 cover sodium extract and qualitative tests for N, S and halogens; pp. 19–21 introduce reaction mechanism, homolytic/heterolytic fission, electrophiles, nucleophiles and inductive effect; pp. 22–30 provide extensive nomenclature tables/examples; and pp. 31–33 cover chain, position, functional and metameric structural isomerism.
Current-syllabus expansion: The typed companion adds tautomerism, geometrical (cis/trans) isomerism, optical isomerism, resonance effect (+R/−R), free-radical summary and steric hindrance because these are part of the current Unit 13 scope but are not developed in the handwritten PDF.
Laboratory safety: Lassaigne’s test traditionally involves highly reactive sodium and corrosive reagents. The notes below explain the principle, ions formed and observations for examination purposes. Actual preparation/testing should be performed only in a properly equipped chemistry laboratory under qualified supervision.
1. Unit Roadmap
Diagram 1: Major learning blocks of Unit 13
2. Source Foundation: Organic Compounds and Classification
Organic chemistry
The branch of chemistry concerned with carbon compounds, especially hydrocarbons and their derivatives.
The branch of chemistry concerned with carbon compounds, especially hydrocarbons and their derivatives.
The uploaded PDF begins with classification into open-chain (acyclic/aliphatic) and cyclic compounds. Cyclic compounds are further divided into homocyclic and heterocyclic; homocyclic compounds may be alicyclic or aromatic.
Diagram 2: Classification chart from the opening source page
3. Common Names and IUPAC Nomenclature
The source first distinguishes common/trivial names from systematic IUPAC names.
| System | Basis | Examples |
|---|---|---|
| Common / trivial | Historical source, use or tradition | Formic acid, acetic acid, acetone |
| IUPAC | Systematic name derived from molecular structure using agreed rules | Methanoic acid, ethanoic acid, propanone |
IUPAC name = Prefix(es) + Word root + Primary suffix + Secondary suffix
4. Word Roots
Word root
Indicates the number of carbon atoms in the selected parent chain.
Indicates the number of carbon atoms in the selected parent chain.
| Carbons | Root | Carbons | Root |
|---|---|---|---|
| 1 | meth | 6 | hex |
| 2 | eth | 7 | hept |
| 3 | prop | 8 | oct |
| 4 | but | 9 | non |
| 5 | pent | 10 | dec |
Current Unit 13 naming scope: Parent chains are required up to six carbon atoms, so meth through hex are essential.
5. Primary and Secondary Suffixes
Primary Suffix: Carbon–Carbon Bond Type
| Bonding | Primary suffix | Class | Example |
|---|---|---|---|
| C–C only | -ane | Alkane | ethane |
| C=C | -ene | Alkene | ethene |
| C≡C | -yne | Alkyne | ethyne |
Secondary Suffix: Principal Functional Group
| Functional group | Class | Suffix when principal | Common prefix when non-principal |
|---|---|---|---|
| –COOH | Carboxylic acid | -oic acid | carboxy- |
| –SO₃H | Sulfonic acid | -sulfonic acid | sulfo- |
| –COOR | Ester | alkyl … -oate | alkoxycarbonyl- |
| –COCl | Acyl chloride | -oyl chloride | chlorocarbonyl- |
| –CONH₂ | Amide | -amide | carbamoyl- |
| –CN | Nitrile | -nitrile | cyano- |
| –CHO | Aldehyde | -al | formyl-/oxo- as context requires |
| >C=O | Ketone | -one | oxo- |
| –OH | Alcohol | -ol | hydroxy- |
| –NH₂ | Amine | -amine | amino- |
6. Prefixes and Substituents
Atoms/groups not selected as the principal suffix are named as prefixes with locants.
| Group | Prefix | Group | Prefix |
|---|---|---|---|
| –CH₃ | methyl- | –Cl | chloro- |
| –CH₂CH₃ | ethyl- | –Br | bromo- |
| –I | iodo- | –NO₂ | nitro- |
| –OR | alkoxy- | –OH | hydroxy- |
| –NH₂ | amino- | –CN | cyano- |
| –CHO | formyl- | >C=O | oxo- |
7. Functional-Group Priority
When more than one functional group is present, the highest-priority group supplies the principal suffix; lower-priority groups are named as prefixes.
Typical school priority: –COOH > –SO₃H > acid derivatives > –CN > –CHO > >C=O > –OH > –NH₂ > C=C > C≡C
The handwritten PDF gives a similar seniority sequence on page 11. Exact IUPAC details can vary with structural context; for Grade 11 problems, use the prescribed priority convention consistently.
8. Core Rules for Writing an IUPAC Name
- Select the parent: choose the appropriate longest chain containing the principal functional group and, where required, the maximum number of multiple bonds.
- Choose the principal functional group: it determines the suffix.
- Number the parent chain: give the principal functional group the lowest possible locant; then apply multiple-bond and substituent locants according to the naming hierarchy.
- Name substituents: methyl, ethyl, chloro, bromo, nitro, methoxy, hydroxy, etc.
- Use multiplicative prefixes: di-, tri-, tetra- for repeated identical substituents.
- Alphabetize different substituents: ignore multiplicative prefixes such as di-/tri- for alphabetization.
- Write locants correctly: commas between numbers; hyphens between numbers and words.
- Include unsaturation locants: e.g., but-1-ene, pent-1,3-diene, but-2-yne.
Source correction note: Some handwritten examples use older or inconsistent spacing/hyphen forms such as “2-methyl butane.” The typed companion uses standardized forms such as 2-methylbutane.
Diagram 3: A practical naming sequence
9. Polyfunctional Compounds
A polyfunctional compound contains two or more functional groups. The principal group is selected according to priority and appears as the suffix; the remaining groups are expressed as prefixes.
Example
CH₃–CH(OH)–COOH
2-hydroxypropanoic acid
Example
CH₃–CO–CH₂–COOH
3-oxobutanoic acid
Example
NC–CH₂–CH(OH)–COOH
3-cyano-2-hydroxypropanoic acid
Rule
The principal group must be included in the parent chain whenever the applicable naming rules require it.
Source connection: Pages 11–13 contain a priority sequence and multiple examples of polyfunctional compounds. The typed examples use standardized IUPAC formatting.
10. Important Nomenclature Examples
| Structure / formula | IUPAC name | Class |
|---|---|---|
| CH₄ | Methane | Alkane |
| CH₃CH₂CH₃ | Propane | Alkane |
| (CH₃)₃CH | 2-Methylpropane | Branched alkane |
| CH₂=CHCH₂CH₃ | But-1-ene | Alkene |
| CH₃CH=CHCH₃ | But-2-ene | Alkene |
| HC≡CCH₂CH₃ | But-1-yne | Alkyne |
| CH₃CH₂Br | Bromoethane | Haloalkane |
| CH₃CH₂OH | Ethanol | Alcohol |
| CH₃OCH₂CH₃ | Methoxyethane | Ether |
| CH₃CHO | Ethanal | Aldehyde |
| CH₃COCH₃ | Propanone | Ketone |
| CH₃COOH | Ethanoic acid | Carboxylic acid |
| CH₃COOCH₃ | Methyl ethanoate | Ester |
| CH₃CONH₂ | Ethanamide | Amide |
| CH₃CH₂NH₂ | Ethanamine | Amine |
| CH₃CH₂NO₂ | Nitroethane | Nitro compound |
Diagram 4: Breaking an IUPAC name into components
11. Homologous Series — Source Foundation
Homologous series
A family of organic compounds with the same functional group and general formula in which successive members usually differ by a –CH₂– unit.
A family of organic compounds with the same functional group and general formula in which successive members usually differ by a –CH₂– unit.
Characteristics
- Same functional group and similar chemical behavior.
- Same general formula for a given homologous family.
- Successive members differ by CH₂ in molecular formula and by 14 u in relative molecular mass.
- Physical properties such as boiling point generally change gradually with molecular mass.
- Members can often be prepared by related general methods.
| Alkane | Alcohol |
|---|---|
| CH₄ — methane | CH₃OH — methanol |
| C₂H₆ — ethane | C₂H₅OH — ethanol |
| C₃H₈ — propane | C₃H₇OH — propanol |
| C₄H₁₀ — butane | C₄H₉OH — butanol |
Source connection: Pages 14–15 define homologous series and list the same core characteristics. This topic mainly overlaps the preceding basic-concept unit but is retained because it is part of the handwritten source.
12. Qualitative Analysis of Organic Compounds
The current syllabus requires detection of nitrogen, sulphur and halogens by Lassaigne’s test.
Principle of Lassaigne’s test
Covalently bound heteroatoms in an organic compound are converted into water-soluble ionic sodium salts in a sodium extract. Those ions are then identified by characteristic qualitative reactions.
Covalently bound heteroatoms in an organic compound are converted into water-soluble ionic sodium salts in a sodium extract. Those ions are then identified by characteristic qualitative reactions.
| Element in compound | Ionic species formed in sodium extract | Test target |
|---|---|---|
| Nitrogen | CN⁻ | Cyanide ion |
| Sulphur | S²⁻ | Sulphide ion |
| N + S together | SCN⁻ | Thiocyanate ion |
| Cl / Br / I | Cl⁻ / Br⁻ / I⁻ | Halide ions |
Safety note: The source describes preparation of sodium extract using fused sodium. That is a supervised laboratory operation. For study, remember the conversion principle and observations; do not attempt sodium fusion outside a laboratory.
Diagram 5: Conceptual sequence of qualitative heteroatom detection
13. Detection of Nitrogen
In the sodium extract, nitrogen is converted to cyanide ion. In the classical test, cyanide first forms a ferrocyanide complex with iron(II), which then gives a characteristic Prussian blue product with iron(III).
Na + C + N → NaCN
Positive observation: Prussian blue coloration / precipitate
Source connection: Page 17 describes alkalinizing the extract, reaction with freshly prepared FeSO₄, heating/cooling and subsequent Fe(III) treatment to obtain Prussian blue.
14. Detection of Sulphur
Sulphur is converted to sulphide in the sodium extract. The source uses lead acetate after acidification, producing black lead sulphide.
2Na + S → Na₂S
S²⁻ + Pb²⁺ → PbS↓
Positive observation: black precipitate
Source connection: Pages 17–18 show the lead-acetate test and identify black PbS as the positive result.
15. Detection of Halogens
Halogens are converted to sodium halides in the sodium extract and then identified through silver-halide precipitates.
NaX + AgNO₃ → AgX↓ + NaNO₃
| Ion | Silver halide | Typical color | Behavior in aqueous ammonia |
|---|---|---|---|
| Cl⁻ | AgCl | White | Dissolves readily |
| Br⁻ | AgBr | Cream / pale yellow | Much less soluble; dissolves in stronger ammonia conditions |
| I⁻ | AgI | Yellow | Insoluble |
Source connection: Page 18 gives white AgCl, pale-yellow AgBr and yellow AgI observations and distinguishes them using ammonia behavior.
Lab-method note: Standard school procedures normally remove interfering cyanide/sulphide before silver-nitrate testing. Follow the laboratory manual and instructor’s procedure rather than improvising from summary notes.
16. Preliminary Idea of Reaction Mechanism
Reaction mechanism
The stepwise pathway by which reactants are converted to products through bond-breaking, bond-making and intermediate species.
The stepwise pathway by which reactants are converted to products through bond-breaking, bond-making and intermediate species.
A balanced chemical equation shows overall stoichiometry; a mechanism explains how the transformation occurs.
17. Homolytic and Heterolytic Bond Fission
Homolytic fission
Symmetrical cleavage of a covalent bond so each atom receives one electron from the shared pair, forming free radicals.
Symmetrical cleavage of a covalent bond so each atom receives one electron from the shared pair, forming free radicals.
A–B → A• + B•
Heterolytic fission
Unsymmetrical cleavage in which one atom receives both bonding electrons, forming ions.
Unsymmetrical cleavage in which one atom receives both bonding electrons, forming ions.
A–B → A⁺ + B⁻ or A⁻ + B⁺
| Feature | Homolysis | Heterolysis |
|---|---|---|
| Electron division | One electron to each atom | Both electrons to one atom |
| Main products | Free radicals | Carbocations/carbanions or related ions |
| Bond cleavage | Symmetrical | Unsymmetrical |
Diagram 6: Homolytic vs heterolytic cleavage
18. Electrophiles, Nucleophiles and Free Radicals
Electrophile (E⁺)
An electron-pair acceptor: an electron-deficient species attracted to electron-rich regions.
An electron-pair acceptor: an electron-deficient species attracted to electron-rich regions.
Nucleophile (Nu:)
An electron-pair donor: an electron-rich species attracted to electron-deficient centers.
An electron-pair donor: an electron-rich species attracted to electron-deficient centers.
Free radical
A species containing an unpaired electron, commonly formed by homolytic bond cleavage.
A species containing an unpaired electron, commonly formed by homolytic bond cleavage.
| Type | Typical examples | Key behavior |
|---|---|---|
| Electrophiles | H⁺, NO₂⁺, BF₃, carbocations | Accept an electron pair |
| Nucleophiles | OH⁻, CN⁻, Cl⁻, NH₃, H₂O | Donate an electron pair |
| Free radicals | Cl•, CH₃• | React through unpaired-electron pathways |
Source connection: Pages 19–20 define bond fission, carbocation/carbanion, electrophiles and nucleophiles. The free-radical idea is present through homolysis and is made explicit here because the current syllabus names it directly.
19. Inductive Effect (+I and −I)
Inductive effect (I effect)
Permanent polarization transmitted through σ bonds because of electronegativity differences or charged substituents.
Permanent polarization transmitted through σ bonds because of electronegativity differences or charged substituents.
+I Effect
Electron-releasing groups push electron density through σ bonds toward the carbon chain. Alkyl groups show a +I effect relative to hydrogen in common school comparisons.
−I Effect
Electron-withdrawing groups pull electron density through σ bonds. Examples include strongly electronegative substituents and groups such as –NO₂, –CN, –COOH and halogens.
Important property: Inductive effect decreases rapidly with increasing distance from the substituent.
Applications
- Explaining relative acidity and basicity.
- Explaining stability of some charged intermediates.
- Explaining bond polarization and dipole moments qualitatively.
Example: Chloroacetic acid is stronger than acetic acid because chlorine withdraws electron density by a −I effect, stabilizing the conjugate-base charge relative to acetate.
Diagram 7: Inductive polarization diminishes along the σ-bond framework
20. Resonance Effect (+R and −R) — Current-Syllabus Expansion
Why this section is marked expansion: The uploaded PDF develops the inductive effect but does not substantially explain resonance effect. The current Unit 13 syllabus explicitly requires +R and −R effects.
Resonance / mesomeric effect
Electron donation or withdrawal through a conjugated π system by delocalization of π electrons or lone-pair electrons.
Electron donation or withdrawal through a conjugated π system by delocalization of π electrons or lone-pair electrons.
+R Effect
A group donates electron density into a conjugated system by resonance.
–OH–OR–NH₂ commonly show +R donation when their lone pair is conjugated with a π system.
−R Effect
A group withdraws electron density from a conjugated system by resonance.
–NO₂–CN–CHO–COR–COOH are common −R groups.
| Feature | Inductive effect | Resonance effect |
|---|---|---|
| Electron movement | Polarization through σ bonds | Delocalization through conjugated π/lone-pair system |
| Distance | Falls rapidly with distance | Can operate throughout a conjugated framework |
| Requirement | Polar σ-bond framework | Conjugation / adjacent p orbitals |
Diagram 8: Conceptual resonance donation
21. Steric Hindrance — Current-Syllabus Expansion
Steric hindrance
Reduction in reaction rate or accessibility caused by the physical crowding of bulky atoms/groups around a reactive center.
Reduction in reaction rate or accessibility caused by the physical crowding of bulky atoms/groups around a reactive center.
Even when an electrophile and nucleophile are electronically suitable, large substituents can make approach to the reaction center difficult.
Key idea: Less crowded reaction centers are often more accessible to attacking reagents than highly substituted, crowded centers. The exact effect depends on the reaction mechanism.
Diagram 9: Physical crowding can hinder reagent approach
22. Isomerism: Definition and Classification
Isomerism
The phenomenon in which compounds have the same molecular formula but differ in the arrangement of atoms or in their spatial arrangement, giving different properties.
The phenomenon in which compounds have the same molecular formula but differ in the arrangement of atoms or in their spatial arrangement, giving different properties.
Diagram 10: Structural and stereoisomerism
23. Chain Isomerism
Chain isomerism
Same molecular formula but different arrangement/branching of the carbon skeleton.
Same molecular formula but different arrangement/branching of the carbon skeleton.
n-Butane
CH₃–CH₂–CH₂–CH₃
2-Methylpropane
CH₃–CH(CH₃)–CH₃
Both have molecular formula C₄H₁₀ but different carbon skeletons.
Source connection: Page 31 defines chain isomerism and gives butane and pentane-family examples.
24. Position Isomerism
Position isomerism
Same carbon skeleton and functional-group type, but the functional group, substituent or multiple bond occurs at a different position.
Same carbon skeleton and functional-group type, but the functional group, substituent or multiple bond occurs at a different position.
Propan-1-ol
CH₃CH₂CH₂OH
Propan-2-ol
CH₃CH(OH)CH₃
1-Chloropropane
CH₃CH₂CH₂Cl
2-Chloropropane
CH₃CHClCH₃
Source connection: Page 32 uses both the propanol and chloropropane pairs.
25. Functional Isomerism
Functional isomerism
Same molecular formula but different functional groups.
Same molecular formula but different functional groups.
| Molecular formula | Isomer 1 | Isomer 2 |
|---|---|---|
| C₂H₆O | Ethanol, CH₃CH₂OH | Methoxymethane, CH₃OCH₃ |
| C₃H₆O | Propanal, CH₃CH₂CHO | Propanone, CH₃COCH₃ |
| C₂H₄O₂ | Ethanoic acid, CH₃COOH | Methyl methanoate, HCOOCH₃ |
Source connection: Page 32 explicitly gives alcohol/ether, aldehyde/ketone and acid/ester pairs.
26. Metamerism
Metamerism
Structural isomerism in which compounds have the same molecular formula and the same polyvalent functional linkage but different alkyl groups on its two sides.
Structural isomerism in which compounds have the same molecular formula and the same polyvalent functional linkage but different alkyl groups on its two sides.
It is commonly discussed for ethers, ketones, secondary amines and related functional classes.
Ether example
CH₃–O–CH₂CH₂CH₃
1-methoxypropane
Metamer
CH₃CH₂–O–CH₂CH₃
ethoxyethane
Ketone example
CH₃COCH₂CH₂CH₃
pentan-2-one
Metamer
CH₃CH₂COCH₂CH₃
pentan-3-one
Source connection: Page 33 defines metamerism and gives pentanone and ether examples.
27. Tautomerism — Current-Syllabus Expansion
Source gap: Tautomerism is required by the current syllabus but is not developed in the uploaded PDF.
Tautomerism
Dynamic equilibrium between readily interconvertible structural forms that differ mainly in the position of a proton and a double bond.
Dynamic equilibrium between readily interconvertible structural forms that differ mainly in the position of a proton and a double bond.
Keto–Enol Tautomerism
CH₃–CO–CH₃ ⇌ CH₂=C(OH)–CH₃keto form ⇌ enol form
The two forms are not resonance structures: atoms, including hydrogen, occupy different positions. They are distinct constitutional forms in equilibrium.
Diagram 11: A simple keto–enol tautomeric pair
28. Geometrical Isomerism (cis/trans) — Current-Syllabus Expansion
Geometrical isomerism
Stereoisomerism caused by restricted rotation, commonly around a C=C bond, producing different spatial arrangements of substituents.
Stereoisomerism caused by restricted rotation, commonly around a C=C bond, producing different spatial arrangements of substituents.
Condition for Simple Alkene cis/trans Isomerism
Each carbon of the double bond must carry two different substituents.
cis-but-2-ene
The two CH₃ groups lie on the same side of the C=C reference plane.
trans-but-2-ene
The two CH₃ groups lie on opposite sides.
Diagram 12: Geometrical isomers of but-2-ene
29. Optical Isomerism — Current-Syllabus Expansion
Optical isomerism
Stereoisomerism in which molecules exist as non-superimposable mirror images called enantiomers.
Stereoisomerism in which molecules exist as non-superimposable mirror images called enantiomers.
A simple Grade 11 indicator is a tetrahedral carbon attached to four different groups, called an asymmetric/chiral carbon.
Example: 2-hydroxypropanoic acid (lactic acid), CH₃–CH(OH)–COOH, has a carbon attached to H, OH, CH₃ and COOH and therefore can exist as two mirror-image forms.
d and l notation: In the syllabus wording, d indicates dextrorotation (rotation of plane-polarized light to the right) and l indicates levorotation (to the left). These optical-rotation symbols should not be confused with the separate D/L configurational system used in advanced stereochemistry.
Diagram 13: Conceptual enantiomeric pair around a chiral carbon
30. Structural vs Stereoisomerism: Comparison
| Type | What changes? | Main subtypes in Unit 13 |
|---|---|---|
| Structural isomerism | Connectivity/order of atom attachment | Chain, position, functional, metamerism, tautomerism |
| Stereoisomerism | Spatial arrangement while connectivity remains the same | Geometrical and optical |
31. Worked Examples
Example 1 — Name a branched alkane
CH₃–CH(CH₃)–CH₂–CH₃
Longest chain = 4 carbons → butane. Methyl substituent is at C-2.
Answer: 2-methylbutane
Example 2 — Number an alkene
CH₂=CH–CH₂–CH₃
Number from the end nearer the double bond.
Answer: but-1-ene
Example 3 — Alcohol with unsaturation
CH₂=CH–CH(OH)–CH=CH₂
Alcohol is principal; number to give –OH the lowest locant. The double bonds occur at 1 and 4.
Answer: pent-1,4-dien-3-ol
Example 4 — Polyfunctional compound
CH₃–CH(OH)–COOH
Carboxylic acid has higher priority than alcohol, so –COOH gives the suffix and –OH becomes hydroxy-.
Answer: 2-hydroxypropanoic acid
Example 5 — Ester
CH₃COOCH₃
The alkyl group attached to oxygen is methyl; the acid-derived part is ethanoate.
Answer: methyl ethanoate
Example 6 — Lassaigne nitrogen test
If a sodium extract gives the characteristic Prussian blue product after the standard iron test sequence, nitrogen is indicated.
Example 7 — Lassaigne sulphur test
Formation of a black PbS precipitate in the prescribed lead-ion test indicates sulphur.
Example 8 — Halogen observation
A white silver-halide precipitate that dissolves readily in aqueous ammonia is consistent with chloride (AgCl).
Example 9 — Identify reagent type
OH⁻ possesses available electron pairs and can donate a pair to an electron-deficient center.
Answer: nucleophile.
Example 10 — Identify bond fission
Cl–Cl → Cl• + •Cl
Each chlorine receives one bonding electron.
Answer: homolytic fission.
Example 11 — Inductive effect and acidity
Why is chloroacetic acid more acidic than acetic acid?
Chlorine exerts a −I effect, withdrawing electron density and stabilizing the conjugate base.
Example 12 — Chain isomerism
Butane and 2-methylpropane have the same formula C₄H₁₀ but different carbon skeletons.
Answer: chain isomers.
Example 13 — Functional isomerism
Ethanol and methoxymethane both have formula C₂H₆O but contain alcohol and ether functional groups respectively.
Answer: functional isomers.
Example 14 — Geometrical isomerism
But-2-ene has two different groups on each double-bonded carbon and therefore exists as cis and trans forms.
Example 15 — Optical isomerism
In 2-hydroxypropanoic acid, the central carbon is attached to H, OH, CH₃ and COOH. Because these four groups are different, the molecule can exist as two non-superimposable mirror-image forms.
32. Common Exam Mistakes
- Calling every carbon-containing compound organic without recognizing common inorganic carbon compounds as exceptions.
- Mixing common/trivial names with systematic IUPAC names in the same answer without identifying which system is used.
- Selecting the longest chain while ignoring the principal functional group.
- Numbering from the wrong end and giving the principal functional group an unnecessarily high locant.
- Forgetting to include the locant of a double or triple bond.
- Writing spaces inside simple IUPAC names such as “2 methyl butane” instead of 2-methylbutane.
- Using commas where hyphens are required, or hyphens between two numerical locants instead of commas.
- Alphabetizing substituents using di-/tri- as though those prefixes determine alphabetical order.
- Using a lower-priority functional group as the suffix when a higher-priority group is present.
- Calling –CHO “ketone” or >C=O “aldehyde.”
- Confusing ester –COOR with ether R–O–R.
- Confusing homologues with isomers. Homologues differ by CH₂; isomers have the same molecular formula.
- Describing Lassaigne’s test as directly testing covalently bound N/S/X without first converting them into ionic species conceptually.
- Attempting to reproduce hazardous sodium-fusion steps outside a supervised laboratory.
- Confusing AgCl, AgBr and AgI colors/solubility behavior.
- Calling homolytic fission an ionic cleavage; homolysis forms radicals.
- Calling heterolytic fission a radical cleavage; heterolysis forms ions.
- Calling every positively charged species an electrophile without considering electron-pair acceptance.
- Calling every negatively charged species a nucleophile without considering electron-pair donation and reaction context.
- Confusing the inductive effect with resonance. Inductive effect operates through σ-bond polarization; resonance requires conjugation.
- Forgetting that inductive effect weakens rapidly with distance.
- Assuming +I and +R mean the same physical electron-displacement mechanism.
- Ignoring steric hindrance when a reaction center is physically crowded.
- Defining isomers as compounds with different molecular formulas; isomers have the same molecular formula.
- Confusing chain and position isomerism.
- Calling ethanol and dimethyl ether position isomers; they are functional isomers.
- Calling keto–enol tautomers resonance structures. Tautomers differ in atom positions and interconvert dynamically.
- Assuming every alkene shows cis/trans isomerism. Each alkene carbon must have two different substituents for the simple cis/trans case.
- Using d/l optical-rotation symbols as though they directly specify absolute molecular configuration.
33. Important Exam Questions
Very Short / Short Questions
- What is meant by IUPAC nomenclature?
- What does a word root indicate in an organic name?
- Differentiate primary and secondary suffixes.
- Write the roots for one to six carbon atoms.
- Write the prefixes for –Cl, –Br, –NO₂, –OH and –NH₂ when used as substituents.
- What is a principal functional group?
- State the general rules for selecting and numbering a parent chain.
- Name CH₃CH(CH₃)CH₂CH₃.
- Name CH₂=CHCH₂CH₃.
- Name CH₃COOCH₃.
- Define homologous series and state four characteristics.
- State the principle of Lassaigne’s test.
- Which ionic species represents nitrogen in sodium extract?
- What observation confirms nitrogen in the classical Lassaigne test?
- How is sulphur indicated in the lead-ion test?
- State the colors of AgCl, AgBr and AgI.
- Define reaction mechanism.
- Differentiate homolytic and heterolytic bond fission.
- Define electrophile and give examples.
- Define nucleophile and give examples.
- What is a free radical?
- Define inductive effect.
- Differentiate +I and −I effects.
- Why does inductive effect decrease with distance?
- Define resonance effect.
- Differentiate +R and −R effects.
- Differentiate inductive effect and resonance effect.
- Define steric hindrance.
- Define isomerism.
- Define chain, position and functional isomerism.
- What is metamerism?
- What is tautomerism?
- What is geometrical isomerism?
- State the condition for cis/trans isomerism in a simple alkene.
- What is optical isomerism?
- What is a chiral/asymmetric carbon?
Long / Descriptive Questions
- Explain the IUPAC nomenclature system with word roots, prefixes and suffixes.
- State and explain the rules for naming branched and unsaturated organic compounds up to six-carbon parent chains.
- Explain nomenclature of polyfunctional organic compounds using functional-group priority.
- Describe the principle and observations used for detection of nitrogen, sulphur and halogens by Lassaigne’s test.
- Explain homolytic and heterolytic fission with suitable examples.
- Write an account of electrophiles, nucleophiles and free radicals.
- Explain +I and −I effects and give applications of inductive effect.
- Explain +R and −R effects and distinguish resonance from inductive effect.
- Define isomerism and classify it into structural and stereoisomerism.
- Explain chain, position, functional and metameric isomerism with examples.
- Explain keto–enol tautomerism.
- Explain geometrical isomerism using cis- and trans-but-2-ene.
- Explain optical isomerism and the idea of a chiral carbon.
Give-Reason / Concept Questions
- Why must the principal functional group receive priority during numbering?
- Why are homologues chemically similar but physically different?
- Why must covalently bound N, S and halogens be converted to ions before classical qualitative testing?
- Why does homolytic cleavage produce radicals?
- Why does a strongly electronegative substituent show a −I effect?
- Why does the inductive effect weaken with distance?
- Why are keto and enol forms not resonance structures?
- Why does but-1-ene not show simple cis/trans isomerism while but-2-ene does?
- Why can a molecule with a suitable asymmetric carbon show optical isomerism?
Exam Strategy
Study the chapter in four blocks: (1) IUPAC naming, (2) Lassaigne qualitative analysis, (3) reaction mechanism/electronic effects, (4) isomerism. The handwritten PDF is especially detailed for naming, so practice structures in both directions: structure → name and name → structure.
Study the chapter in four blocks: (1) IUPAC naming, (2) Lassaigne qualitative analysis, (3) reaction mechanism/electronic effects, (4) isomerism. The handwritten PDF is especially detailed for naming, so practice structures in both directions: structure → name and name → structure.
34. One-Minute Revision
- Unit 13 = Fundamental Principles of Organic Chemistry.
- Current teaching time = 10 hours.
- IUPAC naming scope: parent chains up to six carbons.
- Name pattern: prefixes + word root + primary suffix + secondary suffix.
- Roots: meth, eth, prop, but, pent, hex.
- -ane = single-bond parent; -ene = double bond; -yne = triple bond.
- Principal functional group gives the suffix.
- Other groups are usually written as prefixes.
- Use lowest valid locants and correct comma/hyphen punctuation.
- Homologues differ successively by CH₂.
- Lassaigne test converts covalently bound heteroatoms into ionic species.
- Nitrogen → CN⁻; positive classical test gives Prussian blue.
- Sulphur → S²⁻; Pb²⁺ test gives black PbS.
- Halides give AgCl (white), AgBr (cream/pale yellow), AgI (yellow).
- Homolysis gives free radicals.
- Heterolysis gives ions.
- Electrophile = electron-pair acceptor.
- Nucleophile = electron-pair donor.
- Inductive effect = permanent σ-bond polarization.
- +I releases electron density; −I withdraws electron density.
- Inductive effect weakens rapidly with distance.
- Resonance effect operates through conjugated π/lone-pair delocalization.
- +R donates by resonance; −R withdraws by resonance.
- Steric hindrance is crowding around a reaction center.
- Isomers have the same molecular formula.
- Chain isomers differ in carbon skeleton.
- Position isomers differ in position of a group/bond.
- Functional isomers contain different functional groups.
- Metamers differ in alkyl-group distribution around a polyvalent linkage.
- Tautomers are interconvertible structural forms, commonly keto/enol.
- Geometrical isomerism arises from restricted rotation.
- For simple alkene cis/trans isomerism, each C of C=C needs two different substituents.
- Optical isomers are non-superimposable mirror images.
- A chiral carbon commonly has four different attached groups.
35. Diagram Practice
- Four-block roadmap of Unit 13.
- Classification of organic compounds.
- IUPAC naming workflow.
- Structure-to-name breakdown for 2-methylbutane.
- Lassaigne qualitative-analysis logic.
- Homolytic vs heterolytic bond fission.
- Inductive effect through σ bonds.
- Resonance donation through conjugation.
- Steric hindrance around a reaction center.
- Classification of isomerism.
- Keto–enol tautomerism.
- cis- and trans-but-2-ene.
- Optical isomerism around a chiral carbon.
Source handling: The original Nepal eNotes PDF remains embedded above using the exact Google Drive file supplied by the user: 1MMWqQzmP6Ea65R9ipYcCcl3ELltMJGzn. The uploaded Unit-13-Fundamental-principles-of-organic-Chemistry.pdf contains 33 scanned handwritten pages. The typed companion follows the source closely for nomenclature, homologous-series review, Lassaigne qualitative analysis, reaction-mechanism basics, inductive effect and the structural isomerism types actually shown in the PDF. It also distinguishes material that overlaps the preceding basic-concept unit. To match the verified current Grade 11 Unit 13 syllabus, clearly marked expansion sections add tautomerism, geometrical isomerism, optical isomerism, resonance effect (+R/−R), free-radical emphasis and steric hindrance. These additions are syllabus-aligned explanatory material and are not claimed to have been present in the handwritten PDF. Laboratory chemistry involving reactive sodium and corrosive reagents is described at principle/observation level for study; practical execution belongs in a supervised laboratory. This page is a searchable, responsive study companion and is not a word-for-word transcription.
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