Essential Chemistry Concepts & Organic Reactions

Posted on Jun 18, 2025 in Chemistry

Fundamental Chemistry Definitions

Analytical Chemistry & Solutions

Titration: A technique to determine the concentration of a solution by reacting it with a solution of known concentration.
End Point: The point in a titration at which the indicator changes color, signaling that the reaction is complete.
Equivalence Point: The exact point at which the amount of titrant is chemically equivalent to the substance being titrated.
Titration Error: The difference between the end point and the equivalence point.
Normality (N): The number of gram equivalents of solute per liter of solution.
Normality Factor: The correction factor used to account for the actual strength of a solution compared to its theoretical strength.
Molarity (M): The number of moles of solute per liter of solution.
Standard Solution: A solution of known concentration used in titrations.
Primary Standard Solution: A highly pure, stable compound used to make a standard solution directly.
Secondary Standard Solution: A solution whose concentration is determined by titration against a primary standard.
Deci-normal Solution: A solution with a normality of 0.1 N.

Acids, Bases & Equilibrium

pH of Solution: A measure of hydrogen ion concentration; pH = –log[H⁺].
Degree of Ionization: The fraction of total solute molecules that ionize in solution.
Lewis Concept of Base: A base is a substance that donates a pair of electrons.
Common Ion Effect: The suppression of the dissociation of a weak electrolyte by adding a common ion.
Ionic Product of Water (K_w): The product of H⁺ and OH⁻ ion concentrations in water; at 25°C, K_w = 1×10⁻¹⁴.
Solubility Product (K_sp): The equilibrium constant for the dissolution of a sparingly soluble salt.

Thermodynamics & Kinetics

Entropy (S): A measure of randomness or disorder in a system.
Enthalpy of Formation (ΔH_f): Heat change when one mole of a compound is formed from its elements in standard states.
Heat of Combustion: The heat released when one mole of a substance is completely burned in oxygen.
Gibbs Free Energy (ΔG): Energy available to do work; ΔG = ΔH – TΔS.
Spontaneous Process: A process that occurs without external energy input, usually with a negative ΔG.
Second Law of Thermodynamics: Entropy of an isolated system always increases in a spontaneous process.
First Law of Thermodynamics: Energy cannot be created or destroyed, only changed from one form to another. The total energy of an isolated system stays the same.
First Order Reaction: A reaction whose rate depends linearly on the concentration of one reactant.
Half-life of a Reaction: Time required for half of the reactant to be consumed.
Rate Law: An expression showing how the rate depends on reactant concentrations.
Order of Reaction: The sum of powers of the concentration terms in the rate law.
Rate Constant (k): A proportionality constant in the rate law.
Proper Orientation: The correct spatial arrangement of reacting molecules for a reaction to occur.
Energy of Activation (E_a): Minimum energy required for a reaction to proceed.
Pseudo First Order Reaction: A reaction with multiple reactants, but appears first-order because one reactant is in excess.

Electrochemistry & General Concepts

Redox Reaction

A reaction involving oxidation (loss of electrons) and reduction (gain of electrons).

Electrode Potential

The potential difference between an electrode and its electrolyte.

Reference Electrode

A standard electrode with a known potential used to measure other electrode potentials.

Transition Metal

Elements in groups 3–12; partially filled d-orbitals.

Properties:

Variable oxidation states.
Form colored compounds.
Exhibit catalytic activity.
Form complex ions.

Thomas Slag

A byproduct of steelmaking used as a fertilizer.

Fermentation

Breakdown of organic substances by microorganisms, often producing alcohol or acids.

Homopolymer

A polymer made from one type of monomer.

Copolymer

A polymer made from two or more different monomers.

Clinker

A nodular material produced in the cement kiln and ground to make cement.

Natural Radioactivity

Spontaneous emission of radiation by unstable nuclei found in nature.

Artificial Radioactivity

Radioactivity induced by bombarding stable nuclei with particles.

Radioactivity

The spontaneous emission of particles or rays from unstable atomic nuclei.

Key Explanations in Organic Chemistry

Properties & Reactivity

Why Chloroform is Stored in Dark Bottles with Ethanol

Chloroform slowly oxidizes in the presence of air and light to form phosgene (COCl₂), which is highly toxic. Ethanol acts as a stabilizer by reacting with phosgene to form harmless products, and dark bottles prevent light-induced oxidation.

Why Chloroform Doesn’t Give White Precipitate with Aqueous AgNO₃

Chloroform (CHCl₃) is a covalent compound, and the C–Cl bond does not ionize in aqueous solution. Hence, it doesn’t release Cl⁻ ions to react with AgNO₃ to form AgCl precipitate.

Nucleophilic Substitution Difficulty in Haloarenes

In haloarenes, the halogen is attached to an sp² hybridized carbon of the aromatic ring. Due to resonance and partial double bond character, the C–X bond is stronger, and the electron density on the ring makes it less favorable for nucleophiles to attack.

Ethanol vs. Ethoxyethane: Boiling Point Differences

Ethanol (CH₃CH₂OH) forms strong intermolecular hydrogen bonds due to the –OH group, leading to a higher boiling point. Ethoxyethane (diethyl ether) lacks an –OH group and hence has weaker van der Waals forces.

Why Phenol is More Acidic Than Aliphatic Alcohol

The phenoxide ion formed after phenol loses a proton is stabilized by resonance over the aromatic ring. Aliphatic alkoxides formed from alcohols do not have such resonance stabilization, making phenol more acidic.

Nitrobenzene: Meta-Directing Electrophilic Substitution

The –NO₂ group is an electron-withdrawing group. It deactivates the ortho and para positions by withdrawing electron density via both inductive and resonance effects. This makes the meta position relatively more reactive toward electrophiles.

Chlorobenzene: Ortho/Para Directing Electrophilic Substitution

The lone pair on chlorine can participate in resonance with the aromatic ring, increasing electron density at the ortho and para positions. Although Cl is deactivating overall, it directs new substituents to the ortho/para positions due to resonance.

Danger of Boiling Stored Ether: Peroxide Formation

Ethers can form peroxides upon standing in air, especially in the presence of light. These peroxides are explosive and can detonate when heated or boiled.

Why Ether is Stored in Bottles Containing Iron Wire

Iron acts as a reducing agent and helps in decomposing any peroxides that might have formed, preventing explosion hazards.

Distinguishing Chemical Tests

Distinguishing Ethanamine from N-Methylmethanamine

Test: The carbylamine test. Ethanamine (a primary amine) gives a foul-smelling isocyanide when heated with chloroform and alcoholic KOH. N-methylmethanamine (a secondary amine) does not respond to this test.

Chemical Test: Ethanoic Acid vs. Methanoic Acid

Test: Tollens’ test. Formic acid (methanoic acid) reduces Tollens’ reagent (ammoniacal AgNO₃), forming a silver mirror. Acetic acid (ethanoic acid) does not.

Why Chloroacetic Acid is Stronger Than Acetic Acid

The –Cl group is electron-withdrawing via the inductive effect, stabilizing the carboxylate ion formed after deprotonation, thus increasing acidity.

Why Formic Acid is Stronger Than Acetic Acid

Formic acid lacks any alkyl group. The methyl group in acetic acid is electron-donating, destabilizing the carboxylate ion. Hence, formic acid is stronger.

Why Aniline’s Amino Group is Protected Before Nitration

The –NH₂ group is strongly activating and ortho/para-directing. It may cause multiple substitutions during nitration. Also, it can be oxidized under acidic conditions. Protection (e.g., by acetylation) moderates reactivity and prevents overreaction.

Isomers & Synthesis

Functional Isomers of C₃H₆O: IUPAC Names & Tests

Propanal (aldehyde)
Propan-2-one (acetone, ketone)

Test: Tollens’ test: Propanal gives a silver mirror, propan-2-one does not.

Unsymmetrical Ether C₃H₈O: Williamson Synthesis

Ether: Ethyl methyl ether (CH₃OC₂H₅)
Preparation (Williamson Synthesis):
CH₃ONa + C₂H₅Br → CH₃OC₂H₅ + NaBr

Isomeric Amines of C₃H₉N: IUPAC Naming

Propan-1-amine (primary)
Propan-2-amine (primary)
N-methyl ethanamine (secondary)
Trimethylamine (tertiary)

Organic Chemical Conversions

Halogenoalkane & Alcohol Conversions

1-Bromopropane to 2-Bromopropane and Vice Versa

(a) 1-Bromopropane → 2-Bromopropane:

1-Bromopropane → Propene (Elimination with alcoholic KOH)
Propene → 2-Bromopropane (HBr, Markovnikov addition)

(b) 2-Bromopropane → 1-Bromopropane:

2-Bromopropane → Propene (Elimination)
Propene → 1-Bromopropane (HBr with peroxide – anti-Markovnikov)

1-Propanol to 2-Propanol and Vice Versa

(c) 1-Propanol → 2-Propanol:

1-Propanol → Propanal (Oxidation)
Propanal → Propanone (Oxidation)
Propanone → 2-Propanol (Reduction)

(d) 2-Propanol → 1-Propanol:

2-Propanol → Propanone (Oxidation)
Propanone → Propene (Reduction + dehydration)
Propene → 1-Propanol (Hydroboration–oxidation)

Amine & Aromatic Conversions

Methanamine to Ethanamine and Vice Versa

Methanamine → Ethanamine:

Methanamine → CH₃CN (via Gabriel synthesis or alkylation)
CH₃CN → CH₃CH₂NH₂ (Reduction with LiAlH₄)

Ethanamine → Methanamine:

Ethanamine → Ethanol (Oxidation)
Ethanol → Ethanoic acid (Further oxidation)
Ethanoic acid → Methanamine (Decarboxylation → Methanol → CH₃NH₂)

Phenol to Anisole (Methoxybenzene) and Vice Versa

Phenol → Anisole:
Phenol + CH₃I → Anisole (using NaOH)

Anisole → Phenol:
Anisole + HI (heat) → Phenol + CH₃I

Ethoxyethane to Methoxyethane

Ethoxyethane → Ethanol + Ethyl iodide (Cleavage with HI)
Ethanol → Ethyl bromide → Ethyl magnesium bromide (Grignard)
CH₃I + Na → CH₃⁻ (or CH₃ONa)
CH₃ONa + C₂H₅Br → Methoxyethane

Phenol/Aniline to Azo Dye

Aniline → Azo Dye:

Aniline + NaNO₂ + HCl (0–5°C) → Benzene diazonium chloride
Diazonium salt + Phenol (alkaline medium) → Azo dye (colored compound)

Aldehyde, Ketone & Acid Conversions

Ethanol to 3-Hydroxybutanal

Ethanol → Acetaldehyde (Oxidation)
Aldol condensation: 2 CH₃CHO → CH₃CH(OH)CH₂CHO (3-Hydroxybutanal)

Ethanol to 2-Hydroxypropanoic Acid (Lactic Acid)

Ethanol → Ethanal (Oxidation)
Ethanal + HCN → CH₃CH(OH)CN (cyanohydrin formation)
Hydrolysis: CH₃CH(OH)CN → CH₃CH(OH)COOH

Propanone (Acetone) to 2-Hydroxy-2-Methylpropanoic Acid

Propanone + HCN → Cyanohydrin: CH₃C(OH)(CN)CH₃
Hydrolysis: CH₃C(OH)(COOH)CH₃ (2-Hydroxy-2-methylpropanoic acid)

Phenol to Toluene

Phenol → Benzene (Reduction with Zn)
Benzene + CH₃Cl (AlCl₃ catalyst) → Toluene (Friedel–Crafts alkylation)

Ethanol to Propanoic Acid

Ethanol → Ethanoic acid (Oxidation)
Ethanoic acid → CH₃MgBr (Grignard reagent) + CO₂ → Propanoic acid

Methanamide to Ethanamine

Methanamide → CH₃CN (via dehydration)
CH₃CN → CH₃CH₂NH₂ (Reduction with LiAlH₄)

Key Chemical Reactions & Products

Sodium Benzoate Heated with Soda Lime
Reaction:
C₆H₅COONa + NaOH → C₆H₆ + Na₂CO₃
Product: Benzene (C₆H₆) is formed by decarboxylation.
Phenol Heated with Zinc Dust
Reaction:
C₆H₅OH + Zn → C₆H₆ + ZnO
Product: Benzene is formed.
Chlorobenzene Treated with Chloral
Reaction:
C₆H₅Cl + CCl₃CHO + NaOH → DDT (C₁₄H₉Cl₅)
Product: DDT (Dichlorodiphenyltrichloroethane) is formed.
Ethanol Reacts with Acetic Acid
Reaction:
C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O
Product: Ethyl acetate (an ester) is formed (esterification).
Phenol Treated with Aqueous Br₂
Reaction:
C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr
Product: 2,4,6-Tribromophenol (white precipitate) is formed.
Aniline Treated with Aqueous Br₂
Reaction:
C₆H₅NH₂ + 3Br₂ → C₆H₂Br₃NH₂ + 3HBr
Product: 2,4,6-Tribromoaniline is formed (white precipitate).
Phenol Treated with Benzene Diazonium Chloride
Reaction:
C₆H₅OH + C₆H₅N₂Cl → C₆H₅–N=N–C₆H₄–OH
Product: An azo dye (orange color) is formed.
Ethoxyethane Treated with Excess HI
Reaction:
C₂H₅OC₂H₅ + 2HI → 2C₂H₅I + H₂O
Product: Ethyl iodide and water are formed.
Aldehydes React with Ammonia
Reaction (Methanal):
HCHO + NH₃ → H₂CNH + H₂O
Product: Hexamethylenetetramine or other amine derivatives depending on conditions.
Methanal / Benzaldehyde Treated with NaOH
Reaction (Aldol condensation or Cannizzaro reaction depending on aldehyde):
- Methanal: Cannizzaro reaction → HCOONa + CH₃OH
- Benzaldehyde: Cannizzaro reaction → Sodium benzoate + benzyl alcohol.
Ethanol/Propanone Treated with NaOH
- Ethanol: No specific reaction unless oxidation.
- Propanone (acetone): Aldol condensation → β-hydroxy ketone.
Aldehyde/Ketone Treated with Hydroxylamine
Reaction:
RCHO or RCOR’ + NH₂OH → Oxime
Product: Oximes are formed.
Ethanol Heated with Concentrated H₂SO₄
Reaction (at 170°C):
C₂H₅OH → C₂H₄ + H₂O
Product: Ethene is formed (dehydration).
(At 140°C, it gives diethyl ether.)
Acetic Acid Treated with P₂O₅
Reaction:
CH₃COOH → (CH₃CO)₂O + H₂O
Product: Acetic anhydride is formed (dehydration).