Think of hydrocarbons as simple dal-chawal with no extra masala — they contain only carbon and hydrogen. When all carbons are linked by single bonds, we get saturated alkanes (C_nH_2n+2), like a calm old uncle-aunty couple sipping chai, low in energy but very stable, just like LPG in your kitchen. When there is one double bond, we get unsaturated alkenes (C_nH_2n) — energetic youngsters in a tight hug, reactive like bananas ripening fast. With a triple bond we get alkynes (C_nH_2n-2) — super-tight gym buddies holding three hands, strong enough for a welding torch.

On the basis of structure, if the carbon chain is open like a rope for drying clothes, it is aliphatic — straight chain is a simple rope, branched chain is a family tree with many branches. If it closes into a ring like a steel kada or bangle, it is alicyclic — cyclopropane is a tiny triangular bangle, cyclohexane is a comfortable six-membered bangle. If it has a special six-carbon fragrant ring with delocalized electrons, it is aromatic — like a gajra garland of benzene, extra stable and special.

Remember the picture: calm married uncle = alkane, energetic couple = alkene, triple-grip gym buddies = alkyne, open rope = aliphatic, closed bangle = alicyclic, and fragrant garland = aromatic benzene.

Alkanes are like well-cooked rotis — you can make them by several easy kitchen recipes. Wurtz reaction (2R-X + 2Na → R-R + 2NaX in dry ether) is like a sodium uncle acting as a matchmaker at a wedding hall, joining two friends (alkyl halides) to form a new bond. It works best for symmetrical alkanes, like 2CH₃-Cl → CH₃-CH₃.

Kolbe's electrolysis (2RCOONa → R-R + 2CO₂) is like removing the parcel wrapper — CO₂ bubbles out like steam from a pressure cooker, leaving R-R behind. Decarboxylation (RCOONa + NaOH/CaO → R-H + Na₂CO₃) is fruit-seed removal with soda lime masala — classic lab methane is CH₃COONa → CH₄. You can also reduce an alkyl halide R-X + Zn + H⁺ → R-H like a barber shaving off the X-cap. Finally, hydrogenation (CH₂=CH₂ + H₂ → CH₃-CH₃ over Ni, Sabatier) is like putting ghee on a hungry roti on a hot Ni tawa — the double bond gets filled and becomes fully satisfied.

For physical properties, alkanes are non-polar like oil sharing blankets equally, so they are insoluble in water and float like tadka oil on water. As size grows, boiling point increases because of stronger van der Waals forces, like a bigger blanket being heavier and harder to lift.

Chemically, they show free radical substitution (CH₄ + Cl₂ → CH₃Cl + HCl in sunlight hν) — think of a DJ playing under sunlight. Initiation splits Cl-Cl twins, propagation passes the relay dance, termination stops the music. Combustion (C_nH_2n+2 + O₂ → CO₂ + H₂O + heat) gives the bright LPG stove flame that cooks your food.

Other interesting conversions: controlled oxidation of CH₄ to CH₃OH and HCHO is like roasting roti with controlled heat; isomerization (n-butane → iso-butane with AlCl₃/HCl, 300°C) is shifting the same bricks into a different house shape; aromatization (n-hexane → benzene over Cr₂O₃, 773K) is turning a straight line into a garba circle; pyrolysis/cracking breaks bigger alkanes into smaller ones at high temperature, like breaking a big roti into small pieces in a refinery.

Imagine rotation around a C-C single bond as rotating a chapati on a full cycle wheel. We draw it in two ways: Sawhorse projection is a side view like seeing a horse from the side, and Newman projection is a front view like seeing an auto's headlights from the front – it is like a door hinge view.

For ethane, when two CH₃ groups are at 60° apart it is staggered – like 3 people standing apart comfortably in a market, stable and lower energy by about 12 kJ/mol. When they overlap at 0°, it is eclipsed – crowded Mumbai local with shoulder collisions – higher energy due to torsional strain.

For butane, the most stable is anti at 180° – like two big suitcases kept far apart in an auto, most comfortable. Gauche at 60° is less stable where suitcases come a little close. Eclipsed CH₃-H is unstable, and fully eclipsed CH₃-CH₃ is most unstable like two uncles fighting for the same seat, with a barrier of about 12.5 kJ/mol. Stability order: anti > gauche > eclipsed > fully eclipsed.

We can make alkenes by removing guests from the molecule. From alkynes, we have two kitchen styles: with Lindlar's catalyst (Pd/CaCO₃) we get cis-alkene – like gentle mummy half-frying, both friends sit on the same side of the auto; with Na in liquid NH₃ we get trans-alkene – strong dhaba pressure cooker, friends sit on opposite train seats.

Dehydrohalogenation (R-X + alc. KOH, heat → alkene + KX + H₂O) is like a strict warden ousting an HX guest. Saytzeff's rule says the richer shop gets more customers – the more substituted, more stable alkene is major, so CH₃-CHBr-CH₂-CH₃ mainly gives CH₃-CH=CH-CH₃.

Vicinal dihalides with Zn dust (CH₂Br-CH₂Br + Zn → CH₂=CH₂ + ZnBr₂) is like removing twin earrings with a Zn magnet, and the ponytail double bond appears. Alcohol dehydration (R-OH + conc. H₂SO₄, 170°C → alkene + H₂O) is a thirsty sponge squeezing water from a wet towel – ease order is 3° > 2° > 1°, so ethanol → ethene easily.

The C=C double bond has a free pi-blanket, a free samosa of electrons, so it is electron-rich and loves addition. With H₂/Ni, alkene → alkane (CH₂=CH₂ + H₂ → CH₃-CH₃) – like a wedding chef turning a double bench into two single chairs.

The Br₂ test (C=C + Br₂ → dibromide) is a famous alkene detective – brown colour disappears like haldi wash, confirming unsaturation.

For HX addition, Markovnikov's rule says rich gets richer – X goes to the carbon with less hydrogen, more substituted side. So CH₃-CH=CH₂ + HBr → CH₃-CHBr-CH₃ is major (90%) via a more stable carbocation, order 3° > 2° > 1° like richer house gets the guest. Anti-Markovnikov happens only with HBr + peroxide (ROOR) via radicals, giving CH₃-CH₂-CH₂Br as major. For acid-catalysed hydration (H₂O/H⁺), OH also goes to the richer side (Markovnikov) forming CH₃-CH(OH)-CH₃.

Think of the C=C bond as a weak joint, like a sugarcane elbow joint. Ozonolysis (C=C + O₃ + Zn/H₂O → carbonyls) is like scissors cutting at the joint – it cleaves the double bond into aldehydes and ketones, very useful to find where the double bond was. It is like cutting a mango exactly at the seed. If the carbon had an H, you get aldehyde; if it had two alkyl groups, you get ketone. For example, CH₂=CH₂ gives 2 HCHO.

For oxidation, cold dilute KMnO₄ is gentle mummy – it gives a syn diol (both OH on same side, like malai on paratha on same side) and Baeyer's test – pink KMnO₄ becomes colourless with brown MnO₂. Hot concentrated KMnO₄ is strict – it cuts: =CH₂ → CO₂, =CH-R → R-COOH, =CR₂ → R₂C=O.

Polymerization (nCH₂=CH₂ → -[CH₂-CH₂]_n- polyethylene) is like a mala-beads factory – many small beads (monomers) join into a long garland like polythene bags in the market, like train coaches joining into a long train or sevai chain.

A C≡C triple bond is three hands holding super tightly, formula C_nH_2n-2. For preparation, CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂ is like the old carbide lamp bubbling gas when water touches the hard haldi packet – soda gas. Also, vicinal dihalides R-CHBr-CHBr-R + 2NaNH₂ → R-C≡C-R + 2NaBr + 2NH₃ – two neighbour aunty Br-stickers are removed by a strong sweeper.

Addition is hungry – one triple bond can add two molecules: R-C≡C-R + 2HX/2X₂ → tetrahalo. With water, R-C≡CH + H₂O → (Hg²⁺/H₂SO₄) enol → ketone – water to a dry papad that puffs up into a ketone.

Acidic nature is like a loose milk tooth: only terminal alkynes R-C≡C-H are acidic because sp-hybrid carbon has 50% s-character, more electronegative and holds electrons tightly, so the H leaves easily, unlike strong teeth of alkanes. So R-C≡C-H + NaNH₂ → R-C≡C-Na⁺ + NH₃. This is used as a detective test: only terminal alkyne gives white ppt with Tollens (HC≡CH + 2[Ag(NH₃)₂]OH → Ag-C≡C-Ag ↓ white, silver cap) and red ppt with cuprous chloride (HC≡CH + Cu₂Cl₂/NH₄OH → Cu-C≡C-Cu ↓ red, red bindi). Finally, polymerization 3C₂H₂ → C₆H₆ over red hot Fe tube at 873K – three autos joining to make a big chakri thali benzene ring.

Benzene C₆H₆ is like six friends sitting in a perfect circle, sharing toys equally, with an extra stability of about 150 kJ/mol – like a gol chakki pizza shared equally. Kekule proposed two forms flipping quickly, like the same family posing in two styles during musical chairs – it is dynamic but the same.

The real structure is a hybrid – a regular hexagon with a circle inside. All C-C bonds are 1.39 Å, intermediate between single (1.54 Å) and double (1.34 Å), like cutting a cake into six equal pieces. This resonance gives 150 kJ/mol extra savings, like joint family savings.

Huckel's rule (4n+2) for aromaticity says a compound must be cyclic, planar, conjugated and have (4n+2) pi electrons. So 2, 6, 10 electrons – benzene has 6 – fit perfectly into the auto seats like doughnut-shaped clouds above and below the ring.

We can prepare benzene by 3C₂H₂ → C₆H₆ over red hot Fe (873K) – three rotis making a full thali, or by benzoate + soda lime → benzene like removing a mango seed, and phenol + Zn dust → benzene like scrubbing with a cleaner.

Benzene prefers electrophilic substitution — its rich pi-cloud happily attacks an electrophile to form a sigma complex, then H⁺ leaves, keeping aromaticity intact. Important examples: Nitration (HNO₃/H₂SO₄ → C₆H₅-NO₂), Halogenation (Cl₂/FeCl₃ → C₆H₅-Cl), Sulphonation (H₂SO₄ → C₆H₅-SO₃H), Friedel-Crafts alkylation (RCl/AlCl₃ → C₆H₅-R) and acylation (RCOCl/AlCl₃ → C₆H₅-COR).

Groups show directive effect: o,p-directing activating groups like -OH, -NH₂, -CH₃, -OCH₃ are generous mummies pushing electrons to ortho-para; m-directing deactivating groups like -NO₂, -COOH, -CHO, -CN, -SO₃H are strict principals pulling electrons and directing to meta. Polycyclic aromatic hydrocarbons (PAH) with >2 rings like naphthalene are carcinogenic, like the smoke from burnt roti.