MP Board Class 11th Chemistry Notes Chapter 13 Hydrocarbons

These MP Board Class 11th Chemistry Notes for Chapter 13 Hydrocarbons help students to get a brief overview of all the concepts.

MP Board Class 11th Chemistry Notes Chapter 13 Hydrocarbons

Main methods of preparation of alkanes :

→ Main methods of preparation of alkenes :

→ Main methods of preparation of alkynes:

→ Physical properties of alkanes :

1. Boiling point increases with increase in molecular mass, b.p. of branched chain compounds are lower than that of straight chain compounds.
2. Melting points also increases with increasing molecular mass. Compounds having odd number of carbon atoms have lower value of m.p.
3. Insoluble in water or polar solvents but soluble in non-polar solvents like ether, benzene, etc.
4. Generally, density increases with increasing molecular mass.

→ Chemical properties of hydrocarbons;

• Combustion: Exothermic reactions, give CO₂ and water vapours.
• Alkenes and alkynes decolorize alcoholic KMnO₄ solution.
• Alkyl benzene oxidize into benzoic acid.
• Unsaturated hydrocarbons give addition reactions (H₂, Cl₂, HCI, etc.).
• Addition of HX in unsaturated hydrocarbons is according to MarkownikofFs rule but opposite in presence of peroxide.
• Alkenes, alkynes and arenes ozonolyze and form carbonyl compounds.
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• Polymerization: (a) Ethylene → polyethylene, (b) Propylene → polypropylene, (c) Isoprene → polyisoprene, (d) Vinyl chloride → polyvinyl chloride (PVC), (e) Styrene → polystyrene, (f) Tetrafluoroethene → teflon (PTFE).

(x) Substitution reactions: (a) In alkanes substitution of all hydrogen atoms by halogen atoms take place in presence of sunlight.
(b) Benzene gives halogenation, nitration, sulphonation, alkylation and Friedel-Crafts reaction.
(c) Acetylene and other alkynes give substitution reactions with silver(I) and Cu(I) ions in ammoniacal medium and white and red coloured precipitates of acetylides are formed.

→ Acetylene and others : Alkynes undergo substitution reactions in ammoniacal medium with Silver(I) and Copper(II) ions and form white and red precipitate of acetylides. The ≡ C—H group is of acidic nature.

→ Methods of preparation of Benzene :

→ Alkanes undergo free radical substitution reactions.

→ Alkenes and Alkynes undergo electrophilic addition reaction.

→ Main chemical reaction of benzene is electrophilic substitution reaction.

→ Conformation: Due to free rotation around C – C (single bond), formation of different special arrangements.

→ Alkanes : Saturated hydrocarbons or paraffins, general formula C_nH_2n+2tetrahedral structure, sp³ hybridization, H – C – H bond angle is 109° 28′.

→ Alkenes : Unsaturated hydrocarbons whose general fonnula is C_nH_2n.  Carbon-carbon double bond is present.

→ Alkynes : Unsaturated hydrocarbons whose general formula is C_nH_{2n – 2}. Carbon-carbon triple bond is present.

→ Chirality : Compounds not superimposable on their mirror images.

→ Unsymmetrical carbon atom : Such carbon atom to which four different atoms or groups are linked.

→ Optical isomers : Mirror image isomers which rotate the plane of polarised light in opposite direction equally.

→ Racemic mixture : Mixture of equal amount of d and f forms which is optically inactive.

→ Meso form : Symmetrical molecule with more than one chiral centre which is optically inactive.

→ Markownikoff’s rule : The negative part of polar molecule adds to that carbon atom of an unsymmetrical double bond which contains less number of hydrogen atoms.

→ Kharasch effect: Addition reaction on unsymmetrical alkene in presence of peroxide occurs against Markownikoff’s rule.

→ Huckel’s rule : Compound behaves as Aromatic compound if it contains (4n + 2) π-electrons, mete directing groups : — CHO, – COOH, – NO₂, – C ≡ N,- SO₃H, — COR, — COOR. ortho and para directing groups: – OH, – NH₂, – X, – OR, – R, – NHR, – NHCOCH₃, – CH₃, – C₂H₅.

→ meta directing groups makes the ring inactive towards electrophilic substitution reactions.

→ ortho and para directing groups make the ring active towards electrophilic substitution reagents.

→ Dienes : These are unsaturated hydrocarbons. They contain carbon-carbon double bond.

→ Hydrocarbons are compounds of carbon and hydrogen only. They are mainly obtained from coal and petroleum which are main sources of energy.

→ Liquefied Petroleum Gas (LPG) and Compressed Natural Gas (CNG) which is a domestic fuel and are main source of energy for automobiles. These are also obtained from petroleum.

→ Classification of hydrocarbons on the basis of structure :