Organic Chemistry

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Organic Chemistry — Key Facts for CUET IUPAC naming: longest chain + suffix (ane/ene/yne) + substituents; lowest numbers for functional groups Functional groups: alcohol (-OH), aldehyde (-CHO), ketone (-CO-), carboxylic acid (-COOH), amine (-NH₂), ether (-O-), ester (-COO-), amide (-CONH₂) Isomerism: structural (chain, position, functional group) and stereoisomerism (geometric: cis/trans; optical: enantiomers) Electrophiles: electron-deficient species (H⁺, NO₂⁺, AlCl₃); Nucleophiles: electron-rich species (OH⁻, CN⁻, NH₃) Inductive effect: permanent polarisation of σ bond; +I (alkyl groups) donates e⁻, -I (halogens, -NO₂) withdraws e⁻ ⚡ Exam tip: Carbocation stability: tertiary > secondary > primary > methyl; hyperconjugation from adjacent C-H bonds stabilises carbocations

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🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding of carbon chemistry.

Organic Chemistry — CUET Chemistry Study Guide

Organic chemistry is the chemistry of carbon compounds. Carbon’s unique ability to form four covalent bonds and catenation (C-C bonds) leads to millions of compounds. The tetravalency of carbon and the strength of C-C bonds ($347$ kJ/mol) make organic chemistry vast and diverse.

Hydrocarbons:

• Alkanes (CₙH₂ₙ₊₂): saturated, only single bonds, $sp³$ hybridisation. Methane CH₄, Ethane C₂H₆, Propane C₃H₈. Chemical reactions: halogenation (substitution).
• Alkenes (CₙH₂ₙ): contain C=C double bond, $sp²$ hybridisation. Ethene CH₂=CH₂, Propene CH₃-CH=CH₂. Reactions: addition (H₂, HX, X₂, H₂O), polymerisation.
• Alkynes (CₙH₂ₙ₋₂): contain C≡C triple bond, $sp$ hybridisation. Ethyne (acetylene) HC≡CH. Reactions: addition, acid-catalysed hydration gives aldehyde.

Functional Group Reactions:

• Alcohols (R-OH): formed by hydration of alkenes or Grignard reaction. Classification: primary (RCH₂OH — oxidised to aldehyde then acid), secondary (R₂CHOH — oxidised to ketone), tertiary (R₃COH — not oxidised by mild oxidants).
• Aldehydes and Ketones (R-CHO, R-CO-R’): distinguished by Tollens’ test (aldehyde gives silver mirror), Fehling’s test (aldehyde gives brick-red precipitate). Both undergo nucleophilic addition (HCN, NaHSO₃).
• Carboxylic Acids (R-COOH): acidic (pKₐ 4-5). Reactions: esterification (RCOOH + R’OH → RCOOR’ + H₂O), amide formation (RCOOH + NH₃ → RCONH₂ + H₂O).

Reaction Mechanisms:

• Electrophilic Addition (alkenes): H⁺ adds first (to give more stable carbocation), then nucleophile attacks. Markovnikov’s rule: H adds to C with more H atoms, nucleophile to C with fewer H atoms. Peroxide effect (anti-Markovnikov addition with HBr in peroxide).
• Nucleophilic Substitution (S_N1, S_N2): S_N2 is bimolecular, concerted (backside attack), inversion of configuration. S_N1 is unimolecular, two-step (carbocation intermediate), racemisation. S_N1 favored with stable carbocations (tertiary > secondary), weak nucleophiles, polar protic solvents. S_N2 favored with unhindered substrate (methyl > primary > secondary), strong nucleophiles, polar aprotic solvents.
• Elimination (E1, E2): competing with substitution. E1 favored under same conditions as S_N1; E2 is bimolecular, concerted (requires anti-periplanar geometry in cycloalkanes).

Example: Name the compound CH₃-CH₂-CH(CH₃)-CHO using IUPAC. Longest chain containing aldehyde = 5 carbons (pentanal). Number from aldehyde carbon: position 2 has methyl substituent. Name: 2-methylpentanal. Alternatively, could be named 2-methylvaleraldehyde.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Organic Chemistry — Complete CUET Chemistry Notes

Electronic Effects in Organic Chemistry:

• Inductive effect: permanent polarisation of σ bond due to electronegativity difference. +I effect (alkyl groups donate e⁻ density) and -I effect (electronegative atoms withdraw). Propagates through σ bonds but weakens with distance.
• Resonance effect: delocalisation of π electrons. +R effect (donates e⁻ through p-π conjugation: -OH, -NH₂, -OR) and -R effect (withdraws e⁻: -NO₂, -CN, -COOH, -COOR). Operating in conjugation systems.
• Hyperconjugation: delocalisation of σ electrons (C-H or C-C) into adjacent empty or π orbitals. Explains carbocation stability (tertiary > secondary > primary) and stability of alkenes (more alkyl substituents = more stable).

Stereochemistry:

• Geometric isomerism (cis/trans or E/Z): restricted rotation around C=C double bond. E = trans (higher priority groups on opposite sides), Z = cis (same side). CIP priority rules: higher atomic number at double-bonded atoms wins.
• Optical isomerism: chiral molecules (non-superimposable on mirror images). Contain stereocentre (usually C with four different groups). Enantiomers: rotate plane-polarised light equally in opposite directions. Racemic mixture: 50:50 mixture, optically inactive.
• R/S nomenclature: Assign priorities to four groups (1 = highest, 4 = lowest). If lowest priority is on dashed bond (pointing away), trace 1→2→3. Clockwise = R (rectus), Counter-clockwise = S (sinister).

Named Reactions (CUET frequently tests these):

• Wurtz reaction: 2R-X + 2Na → R-R + 2NaX (alkane coupling)
• Friedel-Crafts alkylation: RCl + AlCl₃ → R⁺ → electrophilic aromatic substitution
• Cannizzaro reaction: Non-enolizable aldehydes (e.g., HCHO, PhCHO) undergo disproportionation in concentrated base: 2R-CHO + OH⁻ → R-CH₂OH + R-COO⁻
• Clemmensen reduction: C=O → CH₂ (Zn/Hg, HCl)
• Haloform reaction: Methyl ketones (CH₃-CO-R) react with I₂/NaOH to give CHI₃ (yellow precipitate) + R-COO⁻

Environmental Organic Chemistry:

• Biodegradable polymers (polylactic acid, polyhydroxyalkanoates) vs persistent plastics (polyethylene, polypropylene)
• DDT and bioaccumulation — lipophilic toxins stored in fatty tissue
• E-waste: flame retardants (PBDEs), plasticizers (phthalates) — endocrine disruptors

CUET Exam Patterns (2022–2024):

• S_N1 vs S_N2 vs E1 vs E2 conditions and products are most frequently tested (2–3 marks)
• IUPAC naming and isomerism questions appear every year
• Reaction mechanisms (carbocation stability, electrophile/nucleophile identification) are common
• Functional group tests (Tollens, Fehling, iodoform) are frequently tested
• Common mistakes: confusing Markovnikov and anti-Markovnikov addition; not knowing which reactions go through carbocation intermediates

⚡ Key insight: When predicting products, first determine the mechanism. Is the substrate primary, secondary, or tertiary? Is the nucleophile strong? Is the solvent protic or aprotic? These factors determine whether S_N2, S_N1, E2, or E1 dominates. Remember: tertiary substrates with strong nucleophiles in protic solvents favor elimination (E1/E2). Primary substrates with strong nucleophiles in aprotic solvents favor S_N2. Never write products that require impossible geometry or violate mechanism rules.

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