Stability of carbocations: 3° > 2° > 1° > CH₃⁺. (CH₃)₃C⁺ (tertiary) is most stable due to hyperconjugation — 9 C−H bonds in 3 methyl groups donate electron density to empty p-orbital. More hyperconjugation = more stability.

Inductive effect (−I, electron withdrawing) depends on electronegativity: F(3.98) > O > N. Order: −F > −OR > −NR₂. Higher electronegativity = stronger electron withdrawal = stronger −I effect.

The actual structure of benzene is a resonance hybrid — not a mixture of structures but a single structure that is a blend of all contributing resonance forms. All C−C bond lengths in benzene are equal (139 pm), intermediate between single (154 pm) and double (134 pm) bonds.

Nucleophile: an electron-rich species that donates an electron pair to an electrophile. H₂O has two lone pairs on oxygen → it is a nucleophile. BF₃, AlCl₃ are Lewis acids (electrophiles). H⁺ is an electrophile (electron deficient).

Carbanion stability is opposite to carbocation: electron-donating groups (alkyl groups) destabilize carbanions. Methyl carbanion (CH₃⁻) is most stable and 3° is least stable. Order: CH₃⁻ > 1° > 2° > 3° (more alkyl groups = more electron density = less stable carbanion).

Nitration of benzene: C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O. The electrophile is NO₂⁺ (nitronium ion). It substitutes H on benzene ring → electrophilic aromatic substitution (EAS). Addition to ethene is electrophilic addition; others are elimination and nucleophilic substitution.

+M effect: lone pair on substituent delocalizes into benzene ring → electron donation. Groups with lone pairs: −NH₂, −OH, −OR, −SH show +M. −NO₂, −CN, −COOH show −M effect (withdraw electrons from ring through resonance).

Hyperconjugation: overlap of σ(C−H) bond orbital (of the methyl group) with the adjacent π bond (C=C). This delocalizes electron density from C−H into the π system, stabilizing the molecule. Also called ‘no-bond resonance’ — one C−H bond contributes to π system.

Acidity order: CH₃COOH (pKa ≈ 4.75) > H₂CO₃ (pKa₁ ≈ 6.35) > C₆H₅OH (pKa ≈ 10) > C₂H₅OH (pKa ≈ 16). Acetic acid is most acidic — the carboxylate ion is stabilized by resonance.

Basicity of amines (in gas phase and in water, aliphatic > aromatic): (CH₃)₂NH > CH₃NH₂ > NH₃ >> C₆H₅NH₂. Dimethylamine is the strongest base — 2 electron-donating methyl groups increase electron density on N. In water, due to solvation, CH₃NH₂ ≈ (CH₃)₂NH but (CH₃)₂NH is generally stronger.

Homolytic fission: each atom gets one electron from the shared pair → produces free radicals (neutral species with unpaired electrons). Heterolytic fission gives ions. Homolytic cleavage is initiated by UV light or heat (radical reactions).

Chain: 4 carbons. COOH at C1, OH at C3. IUPAC: 3-hydroxybutanoic acid. Count from the COOH end: C1(COOH), C2(CH₂), C3(CH(OH)), C4(CH₃).

+I effect: electron-donating through sigma bonds toward the reaction center. Alkyl groups (−CH₃, −C₂H₅, etc.) show +I effect — they push electron density toward the attached atom. All halogens, −NO₂, −CN show −I effect.

Acetylene H−C≡C−H: H−C (1σ), C≡C (1σ + 2π), C−H (1σ). Total: 3σ bonds and 2π bonds. Each carbon is sp hybridized with 2 sp orbitals (for σ bonds) and 2 unhybridized p orbitals (for 2 π bonds in triple bond).

SN2 (Substitution Nucleophilic Bimolecular): concerted (one-step), backside attack by nucleophile, inversion of configuration (Walden inversion), bimolecular rate = k[substrate][nucleophile]. Favored by primary substrates and strong nucleophiles. No carbocation intermediate.

CHO is at C1 (functional group suffix -al). C1=CHO, C2=CH, C3=CH, C4=CH₃. Double bond at C2-C3. IUPAC: but-2-enal. (The common name is crotonaldehyde but IUPAC is but-2-enal.)

Fries rearrangement: phenol ester (ArOCOR) to hydroxyaryl ketone (ArOH with RCOA group at ortho or para position). In presence of Lewis acid (AlCl₃), acyl group migrates from O to the ring. Gives o- and p-hydroxyaryl ketones.

Hückel’s rule for aromaticity: (1) planar, (2) cyclic, (3) fully conjugated (alternating single and double bonds or lone pairs), (4) (4n+2) π electrons (n = 0,1,2…). Example: benzene has 6π electrons (n=1, 4×1+2=6). Cyclobutadiene (4π) is antiaromatic.

CH₃Br + OH⁻ → CH₃OH + Br⁻. OH⁻ is a nucleophile attacking the carbon bearing Br (a leaving group). Since CH₃Br is primary (methyl), reaction is SN2 (bimolecular nucleophilic substitution). Backside attack, inversion (not applicable for CH₃ as it has no chiral center).

Geometrical isomerism requires a C=C double bond with two different groups on each carbon. But-2-ene (CH₃CH=CHCH₃): each sp² carbon has CH₃ and H → different groups on each. Cis: both CH₃ on same side; trans: opposite sides. CH₂=CH₂ has two identical H on each carbon — no geometric isomerism.