General Organic Chemistry (GOC) is the conceptual engine that drives every organic topic in NEET. On average, 3–4 direct GOC questions appear every year, and indirect GOC reasoning underlies dozens of mechanism-based questions across alcohols, amines, aldehydes, and aromatic chemistry. Mastering this topic once pays dividends across the entire organic section.

Carbon and Hybridization

Carbon's defining feature is tetravalency. How it hybridizes determines the shape, bond angles, bond lengths, and reactivity of every organic molecule.

• sp3 hybridization: One s + three p orbitals mix to form four equivalent sp3 hybrid orbitals pointing toward the corners of a tetrahedron. Bond angle: 109.5°. Example: methane (C). s-character: 25%. sp3 bonds are the longest and weakest among the three hybrid types.
• sp2 hybridization: One s + two p orbitals form three sp2 orbitals in a plane (trigonal planar, 120°), with one unhybridized p orbital perpendicular to the plane forming a π bond. Example: ethene (C=C). s-character: 33.3%.
• sp hybridization: One s + one p form two sp orbitals at 180° (linear), with two unhybridized p orbitals forming two π bonds. Example: ethyne (C#C). s-character: 50%. sp bonds are shortest and strongest.

Higher s-character means shorter, stronger bonds and greater electronegativity of the hybrid orbital — an sp carbon is more electronegative than an sp3 carbon, making sp C-H bonds more acidic (pKa ~25 vs ~50 for sp3).

IUPAC Nomenclature

The IUPAC system names organic compounds unambiguously. The four-step rule: (1) find the longest continuous carbon chain carrying the principal functional group; (2) number the chain from the end nearer to the principal group; (3) list substituents alphabetically as prefixes; (4) use the functional group suffix (-ol, -al, -one, -oic acid, -amine). For example, CC(O)C is propan-2-ol (not 2-propanol, which is acceptable but not preferred IUPAC 2013).

Isomerism

Structural (constitutional) isomers share molecular formula but differ in how atoms are connected:

• Chain isomerism: Different carbon skeleton. Butane vs 2-methylpropane (both $C_{4}H_{10}$).
• Position isomerism: Same functional group at different positions. Propan-1-ol vs propan-2-ol.
• Functional group isomerism: Different groups, same formula. Ethanol (CCO) vs dimethyl ether (COC), both $C_{2}H_{6}O$.
• Metamerism: Different alkyl groups on either side of a heteroatom. Methyl propyl ether vs diethyl ether, both $C_{4}H_{10}$O.

Stereoisomers share the same connectivity but differ in spatial arrangement:

• Geometrical (E/Z) isomerism: Requires restricted rotation (C=C or ring) AND different groups on each doubly-bonded carbon. E = higher-priority groups on opposite sides; Z = same side (CIP rules).
• Optical isomerism: Requires a chiral center (four different groups on one carbon). Non-superimposable mirror images are enantiomers.

Electronic Effects

These are the most tested GOC concepts.

Inductive Effect (I): Permanent polarization transmitted through sigma (σ) bonds. +I groups (alkyl groups: -$CH_{3}$, -$C_{2}H_{5}$) push electron density toward the chain. -I groups (-F, -Cl, -Br, -OH, -$NO_{2}$, -COOH, -CN) pull it away. The effect diminishes rapidly — almost vanishes beyond three carbons.

Mesomeric Effect (M): Electron delocalization through conjugated π systems. +M groups (-OH, -$NH_{2}$, -OR, -NHR) donate lone pairs into the π system, increasing electron density. -M groups (-$NO_{2}$, -CHO, -COOH, -CN, -COR) withdraw through π resonance. Note: -OH is simultaneously -I (electronegativity) and +M (lone pair donation) — the +M dominates in aromatic rings, making -OH ortho/para-directing.

Hyperconjugation: A "no-bond resonance" involving σ electrons of a C-H bond alpha (adjacent) to a carbocation's empty p-orbital or to a π bond. More alpha C-H bonds → more hyperconjugative resonance structures → greater stabilization. Propene has 6 alpha-H atoms (2 methyl C-H bonds adjacent to C=C), while 2-methylpropene has 12 — hence 2-methylpropene is more stable.

Reaction Intermediates

Bond breaking initiates reactions. Homolytic fission gives equal sharing → free radicals (neutral, unpaired electron). Heterolytic fission gives unequal sharing → carbocation (C+, empty p-orbital) or carbanion (C-, lone pair).

Carbocation stability: 3° > 2° > 1° > $CH_{3}^{+}$. Alkyl groups stabilize via +I effect and hyperconjugation.

Carbanion stability is exactly reversed: $CH_{3}^{-}$ > 1° > 2° > 3°. Alkyl groups (+I) push electrons toward an already-negative carbon, destabilizing it. This reversal is the single most common NEET trap.

Free radical stability follows carbocation order: 3° > 2° > 1° > $CH_{3}$· (hyperconjugation and +I stabilize the radical center).

Reaction Types

• Substitution: One atom or group replaces another. Common in alkanes (free radical) and alkyl halides (nucleophilic).
• Addition: Two molecules combine into one product across a multiple bond. Common in alkenes and alkynes.
• Elimination: Atoms/groups are removed to form unsaturation (double or triple bond). Opposite of addition.
• Rearrangement: The carbon skeleton reorganizes (e.g., hydride or methyl shift) within a molecule.

NEET Priority Summary: Master the stability orders (carbocation vs carbanion — they are opposite). Know +M groups (-OH, -$NH_{2}$) and -M groups (-$NO_{2}$, -CHO) by heart. Count alpha-H atoms for hyperconjugation questions. Identify whether a compound can show geometrical isomerism by checking both conditions: restricted rotation AND different substituents on each end of the double bond.