OC-01 Essential NEET Facts — High-Yield Bulleted Reference — Summary

Carbon is tetravalent; sp3 gives tetrahedral geometry (109.5°), sp2 gives trigonal planar (120°), sp gives linear (180°).
s-character order: sp > sp2 > sp3 (50% > 33.3% > 25%).
Higher s-character = shorter bond, stronger bond, more electronegative hybrid orbital, more acidic C-H.
sp3 C-H (alkane) is the least acidic; sp C-H (alkyne) is the most acidic among C-H bonds.
IUPAC: longest chain + lowest locant to principal functional group + alphabetical substituent prefixes.
Functional group suffix priority: -COOH > -CHO > C=O > -OH > - $NH_{2}$ .
Structural isomerism: chain, position, functional group, metamerism — same molecular formula, different connectivity.
Geometrical (E/Z) isomerism requires: (1) restricted rotation AND (2) two different groups on each sp2 carbon.
Optical isomerism requires a chiral center: four different groups on one carbon atom.
Inductive effect (+I): alkyl groups donate electron density through σ bonds.
Inductive effect (-I): -F, -Cl, -Br, -I, -OH, - $NO_{2}$ , -COOH, -CN withdraw through σ bonds.
Inductive effect decreases rapidly with distance (negligible beyond 3 carbons).
Mesomeric effect (+M): -OH, - $NH_{2}$ , -OR, -NHR donate lone pair through π conjugation.
Mesomeric effect (-M): - $NO_{2}$ , -CHO, -COOH, -CN, -COR withdraw through π conjugation.
-OH has BOTH -I (through σ) and +M (through π); +M dominates in benzene ring.
Hyperconjugation = no-bond resonance of alpha C-H sigma electrons with adjacent empty p-orbital or π bond.
Number of hyperconjugative structures = number of alpha C-H bonds.
Carbocation stability: 3° > 2° > 1° > $CH_{3}^{+}$ (stabilized by +I effect + hyperconjugation).
Carbanion stability: $CH_{3}^{-}$ > 1° > 2° > 3° (OPPOSITE of carbocation — alkyl groups destabilize negative charge).
Free radical stability: 3° > 2° > 1° > $CH_{3}$ · (mirrors carbocation pattern).
Homolytic fission → free radicals (neutral species with unpaired electron).
Heterolytic fission → carbocation ( $C^{+}$ , empty p-orbital) or carbanion ( $C^{-}$ , lone pair).
Four reaction types: substitution, addition, elimination, rearrangement.
Rearrangement reactions involve hydride ( $H^{-}$ ) or alkyl shifts, converting less stable to more stable carbocations.
NEET trap: confusing carbocation stability order with carbanion stability order — they are exact opposites.
NEET trap: assuming -OH is only +M — it is also -I, but +M dominates in π systems.
NEET trap: thinking hyperconjugation involves C-C bonds — it specifically involves C-H sigma bonds.