Flashcards for NEET Chemistry - Hydrocarbons

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Hydrocarbons

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Hydrocarbons

Hydrocarbons

Compounds of carbon and hydrogen

Saturated hydrocarbons – have carbon-carbon single bonds

Unsaturated hydrocarbons – have carbon-carbon multiple bonds

Wurtz Reaction

Used for the preparation of higher alkanes

Alkyl halides, on treatment with sodium metal in dry ethereal solution, give higher alkanes containing an even number of carbon atoms

Halogenation of Alkanes

Free radical chain mechanism

Rate of reaction of alkanes with halogens is F₂ > Cl₂ > Br₂ > I₂

Rate of replacement of hydrogens of alkanes is 3° > 2° > 1°

Controlled Oxidation of Alkanes

Alkanes give a variety of oxidation products with suitable catalysts, e.g.

1. CH₄ ⟶ CH₃OH with Cu/523K/100atm
2. CH₄ ⟶ HCHO with Mo₂O₃ + Δ
3. C₂H₆ ⟶ CH₃COOH with (CH₃COO)₂Mn

Markovnikov Rule

Addition of hydrogen halides to unsymmetrical alkenes

The negative part of the addendum

(hydrogen halide, here) gets attached to the carbon atom having a lesser number of hydrogen atoms

Peroxide or Kharash Effect

Anti Markovnikov addition of HBr to unsymmetrical alkenes. It proceeds via free radical chain mechanism

Alkane

Containing carbon-carbon single bonds

General formula – C_nH_2n+2

Carbon is sp³ hybridised

C-C bond length is 154 pm and bond enthalpy 348 kJ mol^-1

H-C-H bond angles are of 109.5°

Alkene

Containing carbon-carbon double bonds

General formula – C_nH_2n

Carbon is sp² hybridised

C=C bond length is 134 pm and bond enthalpy 681 kJ mol^-1

Alkyne

Containing carbon-carbon triple bonds

General formula – C_nH_2n-2

Carbon is sp hybridised

C≡C bond length is 120 pm and bond enthalpy 823 kJ mol^-1

H-C-C bond angle – 180°

Aromaticity

Ring system satisfying these criteria:

– planar structure

– complete delocalisation of the π electrons

– (4n + 2) π electrons, where n is an integer (n = 0, 1, 2, . . .) (Hückel Rule)

Friedel-Crafts Alkylation Reaction

Benzene is treated with an alkyl halide in the presence of anhydrous aluminium chloride to form alkyl benzene

C₆H₆ + CH₃Cl ⟶ Toluene (C₆H₅CH₃)+ HCl

Substitution in Mono-substituted Benzene

Ortho and para directing groups:

–OH, –NHR, –OCH3, –CH3, –C2H5, –NH2, –NHCOCH3, etc.

Meta directing groups: –NO2, –CN, –CHO, –COR, –COOH, –COOR, –SO3H, etc.

Also check:

• NEET Chemistry Syllabus
• NEET Chemistry Important Topics
• NEET Chemistry MCQs
• How to Score 160 Plus in NEET Chemistry