Organic chemistry basics

How structures are written

Dash formula: each bond is a line. Condensed: omit some bonds, use subscripts (CH₃CH₂OH).

Bond-line: zig-zag carbon skeleton; C and H on carbon are implied; heteroatoms and H on them are written.

3-D on paper: solid wedge toward you, dashed wedge away.

Open chain, rings, functional groups

Acyclic / aliphatic: open chains, straight or branched.

Alicyclic: carbon rings that behave like aliphatics. Aromatic: benzene-like rings. Heterocyclic: ring with N/O/S etc.

Functional group: the reactive bit that drives the chemistry (–OH, –COOH, C=O, –NH₂…).

Homologous series: same functional group, each next member differs by CH₂. Physical properties drift steadily; chemistry stays in the family.

Naming without panic

Trivial names: old source/property names (formic acid from ants). Fine in speech; papers want IUPAC when asked.

IUPAC skeleton: longest chain with the principal functional group → number so the group gets the lowest locant → prefixes for substituents → suffix for the main group.

Practice beats memorising essays. Start with alkanes, then add double/triple bonds and one functional group.

Isomerism map

Same molecular formula, different arrangement → isomers.

Structural: chain (skeleton), position (where the group sits), functional (different groups), metamerism (different alkyls on either side of a divalent atom like –O–).

Stereo: same connectivity, different spatial arrangement (geometric, optical — Class 11 flags the idea; depth varies by syllabus).

Electronic effects you’ll meet next

Inductive (−I / +I): permanent pull or push through σ bonds; dies out after a few bonds.

Resonance / mesomeric: delocalisation in conjugated π systems.

Electromeric: temporary shift of π electrons when a reagent attacks.

Hyperconjugation: delocalisation involving σ C–H bonds next to an empty or unsaturated centre — used to explain carbocation stability order.

Reaction intermediates

Homolytic break → free radicals (odd electron). Stability roughly 3° > 2° > 1° > CH₃•.

Heterolytic break can give carbocation (C⁺) or carbanion (C^-). Carbocation stability 3° > 2° > 1°; carbanion often reverses that order.

Carbene: divalent carbon with six electrons around it (e.g. :CH₂) — highly reactive.

Electrophiles seek electrons (H⁺, AlCl₃, NO₂⁺…). Nucleophiles donate electron pairs (OH^-, NH₃, CN^-…).