Q3. Draw all possible structural formulae of the compounds having the molecular formula given below

(a) C₃H₈ - Propane

Structural Isomerism Analysis:

Propane (C₃H₈) does not show structural isomerism because with 3 carbon atoms, only one straight-chain arrangement is possible.

CH₃–CH₂–CH₃

Reason: For alkanes, structural isomers begin at C₄H₁₀. With 3 carbons, you cannot have branching without violating carbon's tetravalency.

Number of isomers formula for alkanes: Increases dramatically with carbon number:

  • C₁: 1 isomer (methane)
  • C₂: 1 isomer (ethane)
  • C₃: 1 isomer (propane)
  • C₄: 2 isomers (butane, isobutane)
  • C₅: 3 isomers
  • C₆: 5 isomers
  • C₇: 9 isomers
  • C₈: 18 isomers
  • C₁₀: 75 isomers
  • C₂₀: 366,319 isomers!

(b) C₄H₁₀ - Butane isomers

Two Structural Isomers:

1. Butane (n-butane)

CH₃–CH₂–CH₂–CH₃

IUPAC: Butane

Boiling point: -0.5°C

Straight chain, all carbons in continuous sequence

2. Methylpropane (isobutane)

CH₃–CH–CH₃
   |
   CH₃

IUPAC: 2-Methylpropane

Common: Isobutane

Boiling point: -11.7°C

Branched chain, three-carbon chain with methyl branch

Isomerism type: Chain isomerism (different carbon skeleton)

Physical properties difference: Branched isomer has lower boiling point due to less surface area for London forces.

(c) C₃H₄ - Propyne

Possible Structures:

For C₃H₄, there are actually two possible structural isomers, not just one:

1. Propyne (Methylacetylene)

CH₃–C≡CH

IUPAC: Propyne

Type: Alkyne (triple bond)

Structure: Terminal alkyne with triple bond between C1 and C2

2. Propadiene (Allene)

CH₂=C=CH₂

IUPAC: Propadiene

Type: Diene (cumulated diene)

Structure: Two consecutive double bonds

Note: This is less common but exists

Degree of unsaturation calculation:

DU = (2C + 2 + N - H - X)/2 = (2×3 + 2 - 4)/2 = (6+2-4)/2 = 4/2 = 2

Two degrees of unsaturation means either: two double bonds, one triple bond, one double bond + one ring, or two rings.

Additional possible structures: Cyclopropene (with one double bond in a 3-membered ring) also has formula C₃H₄ but is highly strained.

Q4. Explain the following terms with examples

A. Structural Isomerism

Definition: Structural isomerism is a form of isomerism in which molecules with the same molecular formula have different bonding patterns (different structural formulae).

Example: C₄H₁₀ has two structural isomers:

1. CH₃CH₂CH₂CH₃ (Butane)
2. CH₃CH(CH₃)CH₃ (2-Methylpropane)

Types of structural isomerism:

  1. Chain isomerism (different carbon skeleton)
  2. Position isomerism (different position of functional group)
  3. Functional group isomerism (different functional groups)
  4. Metamerism (different alkyl groups on either side of functional group)

B. Covalent Bond

Definition: A covalent bond is a chemical bond formed by the sharing of electron pairs between atoms.

Example: H₂ (Hydrogen molecule)

H : H or H–H

Key characteristics:

  • Formed between non-metals
  • Sharing of electrons to achieve octet/duplet
  • Can be single, double, or triple bonds
  • Directional in nature
  • Forms discrete molecules

Carbon's special ability: Can form 4 covalent bonds (tetravalency), leading to vast variety of organic compounds.

C. Hetero Atom

Definition: In carbon compounds, a hetero atom is any atom other than carbon and hydrogen that replaces hydrogen in a hydrocarbon chain.

Common hetero atoms:

  • Oxygen (O) - in alcohols, ethers, carbonyls
  • Nitrogen (N) - in amines, amides, nitriles
  • Sulfur (S) - in thiols, sulfides
  • Halogens (F, Cl, Br, I) - in alkyl halides
  • Phosphorus (P) - in phosphates

Example: Ethanol (C₂H₅OH)

CH₃–CH₂–OH

Here, O is the hetero atom replacing H in ethane (C₂H₆).

D. Functional Group

Definition: An atom or group of atoms that determines the chemical properties of an organic compound.

Examples:

Functional Group Example Suffix/Prefix
–OH (Hydroxyl) CH₃CH₂OH -ol (ethanol)
–CHO (Aldehyde) CH₃CHO -al (ethanal)
–COOH (Carboxyl) CH₃COOH -oic acid (ethanoic acid)
–C=O (Ketone) CH₃COCH₃ -one (propanone)

Importance: Determines reactivity, physical properties, and classification of organic compounds.

E. Alkane

Definition: Saturated hydrocarbons containing only single bonds between carbon atoms. General formula: CₙH₂ₙ₊₂

Examples:

CH₄ - Methane
C₂H₆ - Ethane
C₃H₈ - Propane
C₄H₁₀ - Butane

Characteristics:

  • All C–C bonds are single (σ bonds)
  • Saturated (maximum hydrogen possible)
  • Relatively unreactive (undergo substitution)
  • Undergo combustion to CO₂ + H₂O
  • Found in petroleum, natural gas

Naming: Prefix indicates number of carbons + "ane" suffix.

F. Unsaturated Hydrocarbon

Definition: Hydrocarbons containing at least one double or triple bond between carbon atoms.

Examples:

CH₂=CH₂ - Ethene (alkene)
CH≡CH - Ethyne (alkyne)
CH₃–CH=CH₂ - Propene

Types:

  1. Alkenes: Contain C=C double bonds (CₙH₂ₙ)
  2. Alkynes: Contain C≡C triple bonds (CₙH₂ₙ₋₂)

Characteristics:

  • More reactive than alkanes
  • Undergo addition reactions
  • Can be hydrogenated to alkanes
  • Decolorize bromine water (test for unsaturation)

G. Homopolymer

Definition: A polymer formed from only one type of monomer unit.

Examples:

Homopolymer Monomer Uses
Polyethylene CH₂=CH₂ (Ethene) Plastic bags, bottles
Polypropylene CH₃–CH=CH₂ (Propene) Containers, textiles
PVC CH₂=CH–Cl (Vinyl chloride) Pipes, cables
Teflon CF₂=CF₂ (Tetrafluoroethene) Non-stick coatings

Contrast with copolymer: Made from two or more different monomers.

H. Monomer

Definition: A small molecule that can combine with other monomers to form a polymer through chemical bonding.

Example: Vinyl chloride is the monomer for Polyvinyl chloride (PVC)

n CH₂=CH–Cl → [–CH₂–CHCl–]ₙ

Characteristics of monomers:

  • Usually contain double bonds or reactive functional groups
  • Low molecular weight
  • Can undergo addition or condensation polymerization
  • Often gases or liquids at room temperature

Other examples:

  • Ethylene → Polyethylene
  • Styrene → Polystyrene
  • Caprolactam → Nylon-6
  • Glucose → Starch/Cellulose

I. Reduction

Definition: A chemical reaction in which a substance gains electrons, or decreases its oxidation state.

Example: Conversion of an aldehyde to an alcohol

CH₃CHO + 2[H] → CH₃CH₂OH

Ethanal → Ethanol

In organic chemistry:

  • Addition of hydrogen (hydrogenation)
  • Removal of oxygen
  • Gain of electrons
  • Decrease in oxidation number of carbon

Common reducing agents: LiAlH₄, NaBH₄, H₂ with catalyst (Ni, Pd, Pt).

Other examples:

R–NO₂ → R–NH₂ (Nitro to amino)
R–COOH → R–CH₂OH (Acid to alcohol)

J. Oxidant

Definition: A substance that causes oxidation by accepting electrons or providing oxygen to another substance.

Examples:

Oxidizing Agent Formula Common Uses
Potassium permanganate KMnO₄ Oxidation of alcohols to carbonyls
Potassium dichromate K₂Cr₂O₇ Alcohol oxidation (orange→green)
Ozone O₃ Oxidative cleavage of alkenes
Hydrogen peroxide H₂O₂ Bleaching, oxidation reactions
Tollens' reagent [Ag(NH₃)₂]⁺ Test for aldehydes (silver mirror)

In organic reactions:

CH₃CH₂OH → CH₃CHO → CH₃COOH

Primary alcohol → Aldehyde → Carboxylic acid (using K₂Cr₂O₇/KMnO₄)

Characteristics: Oxidants themselves get reduced during the reaction.

Q5. Write the IUPAC name of the following structural formulae

A. CH₃–CH₂–CH₂–CH₃

CH₃–CH₂–CH₂–CH₃

Step-by-step naming:

  1. Identify longest continuous carbon chain: 4 carbons → "but"
  2. All bonds are single → alkane → suffix "ane"
  3. No branches/substituents
  4. No functional groups other than C–C and C–H bonds

IUPAC Name: Butane

Type: Straight-chain alkane

Molecular formula: C₄H₁₀

Common name: n-Butane

B. CH₃–CHOH–CH₃

CH₃–CHOH–CH₃

Step-by-step naming:

  1. Longest carbon chain: 3 carbons → "prop"
  2. Functional group: –OH (hydroxyl) → alcohol → suffix "ol"
  3. Locate –OH group: On carbon #2
  4. Combine: propane → drop "e" → propanol
  5. Specify position: propan-2-ol

IUPAC Name: Propan-2-ol

Alternative name: Isopropyl alcohol

Type: Secondary alcohol

Common uses: Rubbing alcohol, solvent, disinfectant

C. CH₃–CH₂–COOH

CH₃–CH₂–COOH

Step-by-step naming:

  1. Longest carbon chain including carboxyl carbon: 3 carbons → "prop"
  2. Functional group: –COOH (carboxyl) → carboxylic acid → suffix "oic acid"
  3. Carboxyl carbon is always C1 in numbering
  4. Combine: propane → drop "e" → propanoic acid

IUPAC Name: Propanoic acid

Common name: Propionic acid

Type: Carboxylic acid

Natural occurrence: In sweat, dairy products

D. CH₃–CH₂–NH₂

CH₃–CH₂–NH₂

Step-by-step naming:

  1. Longest carbon chain: 2 carbons → "eth"
  2. Functional group: –NH₂ (amino) → amine → suffix "amine"
  3. No position number needed for primary amines with small chains

IUPAC Name: Ethanamine

Common name: Ethylamine

Type: Primary amine

Characteristics: Fishy odor, basic in nature

E. CH₃–CHO

CH₃–CHO

Step-by-step naming:

  1. Longest chain including carbonyl carbon: 2 carbons → "eth"
  2. Functional group: –CHO (aldehyde) → suffix "al"
  3. Aldehyde carbon is always C1
  4. Combine: ethane → drop "e" → ethanal

IUPAC Name: Ethanal

Common name: Acetaldehyde

Type: Aldehyde

Important: Produced in alcohol metabolism, used in silver mirror test

F. CH₃–CO–CH₂–CH₃

CH₃–CO–CH₂–CH₃

Step-by-step naming:

  1. Longest carbon chain: 4 carbons → "but"
  2. Functional group: C=O (ketone) → suffix "one"
  3. Locate carbonyl group: On carbon #2
  4. Combine: butane → drop "e" → butanone
  5. Specify position: butan-2-one or simply butanone

IUPAC Name: Butan-2-one

Common name: Methyl ethyl ketone (MEK)

Type: Ketone

Uses: Industrial solvent, nail polish remover

IUPAC Naming Rules Summary:

  1. Select parent chain: Longest continuous carbon chain containing functional group
  2. Number the chain: Give lowest numbers to functional groups/substituents
  3. Identify substituents: Name and locate branches (methyl, ethyl, etc.)
  4. Name functional group: Use appropriate suffix (or prefix for some groups)
  5. Combine: Substituents (in alphabetical order) + parent chain + functional group suffix
  6. Punctuation: Numbers separated by commas, numbers and letters by hyphens

Q6. Identify the type of reaction in the following carbon compound reactions

a. CH₃–CH₂–CH₂–OH → CH₃–CH₂–COOH

CH₃–CH₂–CH₂–OH → CH₃–CH₂–COOH

Reaction Type: Oxidation reaction

Explanation:

  • Primary alcohol (propanol) oxidized to carboxylic acid (propanoic acid)
  • Oxidation state of carbon increases
  • Common oxidants: KMnO₄, K₂Cr₂O₇
  • Intermediate aldehyde may form first

b. CH₃–CH₂–CH₃ → 3CO₂ + 4H₂O

CH₃–CH₂–CH₃ + 5O₂ → 3CO₂ + 4H₂O

Reaction Type: Combustion reaction

Explanation:

  • Complete combustion of propane
  • Exothermic reaction (releases heat)
  • Produces CO₂ and H₂O
  • Used as fuel

c. CH₃–CH=CH–CH₃ + Br₂ → CH₃–CHBr–CHBr–CH₃

CH₃–CH=CH–CH₃ + Br₂ → CH₃–CHBr–CHBr–CH₃

Reaction Type: Addition reaction

Explanation:

  • Electrophilic addition to alkene (but-2-ene)
  • Bromine adds across double bond
  • Test for unsaturation (decolorizes Br₂)
  • Forms vicinal dibromide

d. CH₃–CH₃ + Cl₂ → CH₃–CH₂–Cl + HCl

CH₃–CH₃ + Cl₂ → CH₃–CH₂–Cl + HCl

Reaction Type: Substitution reaction

Explanation:

  • Free radical substitution of alkane
  • Requires UV light or heat
  • Chlorine replaces hydrogen
  • Produces mixture of products

e. CH₃–CH₂–CH₂–CH₂–OH → CH₃–CH₂–CH=CH₂ + H₂O

CH₃–CH₂–CH₂–CH₂–OH → CH₃–CH₂–CH=CH₂ + H₂O

Reaction Type: Dehydration reaction

Explanation:

  • Elimination of water from alcohol
  • Forms alkene (but-1-ene)
  • Acid catalyst required (conc. H₂SO₄)
  • Follows Saytzeff's rule for major product

f. CH₃–CH₂–COOH + NaOH → CH₃–CH₂–COO⁻Na⁺ + H₂O

CH₃–CH₂–COOH + NaOH → CH₃–CH₂–COONa + H₂O

Reaction Type: Neutralization reaction

Explanation:

  • Acid-base reaction
  • Carboxylic acid + base → salt + water
  • Forms sodium propanoate (soap-like compound)
  • Exothermic

g. CH₃–COOH + CH₃–OH → CH₃–COO–CH₃ + H₂O

CH₃–COOH + CH₃–OH → CH₃–COO–CH₃ + H₂O

Reaction Type: Esterification reaction

Explanation:

  • Condensation of acid and alcohol
  • Forms ester (methyl ethanoate) + water
  • Acid catalyst (conc. H₂SO₄)
  • Reversible reaction
  • Fruity odor of ester

Organic Reaction Types Summary:

Reaction Type General Form Example Key Feature
Substitution R–X + Y → R–Y + X CH₄ + Cl₂ → CH₃Cl + HCl One group replaces another
Addition C=C + XY → C–C
X  Y		 CH₂=CH₂ + HBr → CH₃–CH₂Br Adds to multiple bonds
Elimination R–CH₂–CH₂–X → R–CH=CH₂ + HX CH₃CH₂OH → CH₂=CH₂ + H₂O Removes atoms to form π bond
Oxidation Increase in O or decrease in H CH₃CH₂OH → CH₃COOH Increase in oxidation state
Reduction Increase in H or decrease in O CH₃CHO → CH₃CH₂OH Decrease in oxidation state

Q7. Write structural formulae for the following IUPAC names

A. Pent-2-one

Analysis:

  • "Pent" = 5 carbon chain
  • "2-one" = ketone group at carbon #2
  • General formula for ketone: R–CO–R'

Structural Formula:

CH₃–CO–CH₂–CH₂–CH₃

Alternative representation:

CH₃–C–CH₂–CH₂–CH₃
   ∥
   O

B. 2-Chlorobutane

Analysis:

  • "Butane" = 4 carbon alkane
  • "2-Chloro" = chlorine at carbon #2
  • Chloro is prefix (halogen substituent)

Structural Formula:

CH₃–CHCl–CH₂–CH₃

Stereochemistry: Chiral center at C2 (asymmetric carbon)

C. Propan-2-ol

Analysis:

  • "Propane" = 3 carbon chain
  • "2-ol" = alcohol group at carbon #2
  • Secondary alcohol

Structural Formula:

CH₃–CHOH–CH₃

Common name: Isopropyl alcohol

D. Methanal

Analysis:

  • "Meth" = 1 carbon
  • "al" = aldehyde group
  • Simplest aldehyde

Structural Formula:

H–CHO

Alternative representations:

H–C–H
   ∥
   O

Common name: Formaldehyde

E. Butanoic acid

Analysis:

  • "Butane" = 4 carbon chain
  • "oic acid" = carboxylic acid group
  • Carboxyl carbon is C1

Structural Formula:

CH₃–CH₂–CH₂–COOH

Given in question: CH₃CH₂CH₂COOH ✓

Common name: Butyric acid (butter odor)

F. 1-Bromopropane

Analysis:

  • "Propane" = 3 carbon alkane
  • "1-Bromo" = bromine at carbon #1
  • Primary alkyl halide

Structural Formula:

CH₃–CH₂–CH₂–Br

Alternative: Br–CH₂–CH₂–CH₃

G. Ethanamine

Analysis:

  • "Ethane" = 2 carbon chain
  • "amine" = amino group (–NH₂)
  • Primary amine

Structural Formula:

CH₃–CH₂–NH₂

Common name: Ethylamine

H. Butanone

Analysis:

  • "Butane" = 4 carbon chain
  • "one" = ketone group
  • Default position for ketone is C2 in butane

Structural Formula:

CH₃–CO–CH₂–CH₃

Same as Pent-2-one? No - butanone has 4 carbons total, pent-2-one has 5

Common name: Methyl ethyl ketone (MEK)

Q8. Answer the following questions

A. What causes the existence of a large number of carbon compounds?

Key Reasons for Vast Number of Carbon Compounds:

Property Explanation Consequence
Catenation Ability to form strong covalent bonds with other carbon atoms Forms chains (straight, branched, rings) of various lengths
Tetravalency Four valence electrons, can form 4 covalent bonds Three-dimensional structures, multiple bonding patterns
Multiple Bond Formation Can form single, double, and triple bonds Different degrees of unsaturation (alkanes, alkenes, alkynes)
Isomerism Same molecular formula, different structures Structural isomers, stereoisomers increase variety
Combination with Heteroatoms Bonds with O, N, S, halogens, etc. Functional groups → different compound classes

Statistical perspective:

  • Known organic compounds: ~10 million+
  • Known inorganic compounds: ~1.5 million
  • Theoretical possible organic compounds: Virtually infinite
  • New compounds synthesized daily in labs worldwide

Comparison with silicon: Silicon also shows catenation but weaker Si–Si bonds, fewer stable compounds.

B. Saturated hydrocarbons are classified into three types. Name them with one example each.

Three Types of Saturated Hydrocarbons (Alkanes/Cycloalkanes):

1. Straight-chain Alkanes

Continuous unbranched carbon chain

CH₃–CH₂–CH₂–CH₃

Example: Butane (n-butane)

General formula: CₙH₂ₙ₊₂

2. Branched-chain Alkanes

Carbon chain with side branches

CH₃–CH–CH₃
   |
   CH₃

Example: 2-Methylpropane (isobutane)

Feature: Lower boiling point than straight chain

3. Cycloalkanes (Ring structure)

Carbon atoms arranged in a ring

  CH₂–CH₂
 /     \
CH₂   CH₂
 \     /
  CH₂–CH₂

Example: Cyclohexane (C₆H₁₂)

General formula: CₙH₂ₙ

Note: All are saturated (only single bonds), differ in carbon skeleton arrangement.

C. Give any four functional groups containing oxygen as a hetero atom. Write one example each.

Oxygen-Containing Functional Groups:

Functional Group Structure Example IUPAC Name
Alcohol –OH CH₃CHOHCH₃ Propan-2-ol
Aldehyde –CHO HCHO Methanal
Carboxylic Acid –COOH CH₃CH₂COOH Propanoic acid
Ketone >C=O CH₃COCH₃ Propanone
Ether –O– CH₃OCH₃ Methoxymethane
Ester –COO– CH₃COOCH₃ Methyl ethanoate

D. Name three functional groups containing different hetero atoms with examples.

Functional Groups with Different Heteroatoms:

1. Nitrogen-containing: Amine

CH₃–CH₂–NH₂

Example: Ethanamine

Heteroatom: Nitrogen (N)

Characteristic: Basic, fishy odor

2. Oxygen-containing: Alcohol

CH₃–CHOH–CH₃

Example: Propan-2-ol

Heteroatom: Oxygen (O)

Characteristic: Hydrogen bonding, polar

3. Halogen-containing: Alkyl halide

CH₃–CHCl–CH₂–CH₃

Example: 2-Chlorobutane

Heteroatom: Chlorine (Cl)

Characteristic: Good leaving group, reactive

Other heteroatoms:

  • Sulfur: Thiol (–SH), Sulfide (–S–)
  • Phosphorus: Phosphate (–OPO₃²⁻)
  • Multiple heteroatoms: Amide (–CONH₂), Nitro (–NO₂)

F. What is vinegar and gasohol? State their uses.

Vinegar and Gasohol:

Vinegar

Composition: 5-8% acetic acid (CH₃COOH) in water, plus trace compounds

Production: Fermentation of ethanol by acetic acid bacteria

Chemical: CH₃CH₂OH + O₂ → CH₃COOH + H₂O

Uses:

  • Culinary: Salad dressings, pickling, flavoring
  • Cleaning: Natural disinfectant, descaling agent
  • Odor removal: Neutralizes smells
  • Health: Folk remedy, blood sugar control
  • Gardening: Weed killer, pH adjustment

Gasohol

Composition: Mixture of gasoline (petrol) and alcohol (usually ethanol)

Common blends: E10 (10% ethanol, 90% gasoline), E85 (85% ethanol)

Uses:

  • Alternative fuel: For gasoline engines with little/no modification
  • Environmental: Reduces greenhouse gas emissions
  • Renewable: Ethanol from biomass (corn, sugarcane)
  • Octane booster: Increases fuel octane rating
  • Energy security: Reduces petroleum dependence

Advantages: Renewable, cleaner burning

Disadvantages: Lower energy density, may damage older engines

G. What is a catalyst? Give one example of a catalytic reaction.

Catalysts in Chemistry:

Definition: A catalyst is a substance that increases the rate of a chemical reaction without itself being consumed or permanently changed.

Key characteristics:

  • Lowers activation energy
  • Not consumed in reaction (regenerated)
  • Does not change equilibrium position
  • Specific to particular reactions
  • Can be heterogeneous or homogeneous

Example: Haber Process for Ammonia Synthesis

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Catalyst: Iron (Fe) with promoters (Al₂O₃, K₂O)

Conditions: 400-450°C, 150-200 atm pressure

Mechanism: Adsorption of N₂ and H₂ on iron surface weakens bonds

Other important catalytic reactions:

  • Contact Process: SO₂ → SO₃ (V₂O₅ catalyst)
  • Hydrogenation: Alkenes → Alkanes (Ni, Pd, Pt catalysts)
  • Catalytic cracking: Petroleum refining (zeolite catalysts)
  • Enzymatic reactions: Biological catalysts (enzymes)

Importance: ~90% of chemical industrial processes use catalysts for efficiency and selectivity.

Carbon Compounds: Key Concepts Summary

Concept Definition Examples Key Points
Hydrocarbons Compounds containing only C and H CH₄, C₂H₄, C₆H₆ Basis of petroleum, classified as aliphatic/aromatic
Functional Groups Atom/group determining chemical properties –OH, –CHO, –COOH, –NH₂ Enables classification and prediction of reactions
Isomerism Same formula, different structures C₄H₁₀: butane & isobutane Structural, stereoisomerism; increases compound diversity
IUPAC Naming Systematic naming of organic compounds CH₃CH₂OH = Ethanol Prefix + parent + suffix; indicates structure clearly
Homologous Series Series with same functional group, CH₂ difference Alkanes: CH₄, C₂H₆, C₃H₈ Gradual change in properties; same general formula
Reaction Types Different ways organic compounds react Substitution, addition, elimination Depends on functional groups and conditions
Polymers Large molecules from repeating monomers Polyethylene, PVC, Nylon Addition/condensation polymerization; plastics, fibers