Hydrocarbons, JEE Main Notes JEE Notes | EduRev

JEE Revision Notes

JEE : Hydrocarbons, JEE Main Notes JEE Notes | EduRev

The document Hydrocarbons, JEE Main Notes JEE Notes | EduRev is a part of the JEE Course JEE Revision Notes.
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  • Compounds of carbon and hydrogen.
  • Classification of Hydrocarbons:
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Alkane

  • Open chain saturated hydrocarbon with general formula (CnH2n+2). 
  • All the C atoms are single bonded i.e. sp3 hybridised.

Conformations of Alkane

  • Conformations are the different arrangement of atoms that can be converted into one another by rotation about single bonds. 
  • Eclipsed Conformation: H atoms on two adjacent carbon atoms are closest to each other i.e. dihedral angle is 0.
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev
  • Staggered Conformation: H atoms on two adjacent carbon atoms are farthest to each other i.e. dihedral angle is 60.
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Preparation of Alkanes:

  • Reduction of Alkyl Halides:
    RX + Zn: + H+  → RH + Zn2+ + X-
    4RX + LiAlH4    → 4RH + LiX + AlX3 (X≠ F)                    
    RX + (n - C4H9)3 SnH  → R-H + (n - C4H9)3 SnX
  • Grignard Reagent:
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev         
  • Hydrogenation of Alkenes:
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev
  • Wurtz Reaction:
    2RX  + 2Na  → R-R + 2NaX
    2Na + 2CH3CH2CH2Cl  →  CH3CH2CH2CH2-CH2CH3 + 2NaCl
  • Corey House Reaction:
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev
  • Decarboxylation of a mixture of the sodium salt of a carboxylic acid:
    RCOONa +NaOH(CaO) → RH +  Na2CO3
  •  Kolbe's electrolytic method:
    2 RCOOK + 2H2O → R-R + 2CO2 + H2+ 2KOH

 Chemical Properties of Alkane

  • Direct Halogenation
    RH + X2→ RX + HX
    Order of Reactivity of X2:    F2 > Cl> Br2; I2 does not react
    a. Initiation Step
    Cl-ClHydrocarbons, JEE Main Notes JEE Notes | EduRev2Cl.
    b. Propagation Step
    H3C-H +Cl → H3C + H-Cl
    H3C + Cl-Cl → H3C-Cl +Cl
    c. Termination Step 
    Cl + Cl →Cl-Cl
    H3C + H3C → H3C-CH3
    Cl + H3C → Cl-CH3
  • Nitration 
    Nitration of alkane is made by heating vapours of alkanes and HNOat about 400oC to give nitroalkanes.
    This is also known as vapour phase nitration.
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev
  • Combustion:
    Alkanes burn readily with non luminous flame in presence of air or oxygen to give CO2 & water along with evolution of heat.
    C2H6 + 7O→ CO2 +6H2O + heat
  • Aromatization
    Alkanes having six to 10 carbon atoms are converted into benzene and its homologues at high pressure and temperature in presence of catalyst.
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev
  • Oxidization of 30 alkane:
    Tertiary alkanes are oxidized to tertiary alcohols by KMnO4
     R3CH + KMnO4 → R3COH

Alkene (olefins)

  • Open chain, Unsaturated hydrocarbons with general formula (CnH2n).
  • At least one  >c=c<  (double bond) group i.e. sp2 hybridisation, is present throughout the chain.
  • Allene: alkene molecule in which at least one C has double bonds with each of the adjacent carbon i.e. -c=c=c- group. 
  • Isomeric with saturated cycloalkanes.
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Geometric Isomers:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
Z is used if the higher - priority substituents on each C are on the same side of the double bond. letter E is used if they are on opposite sides
Hydrocarbons, JEE Main Notes JEE Notes | EduRev         

Heats of Hydrogenation: Heat of hydrogenation increases with increase in stability of alkene.
Hydrocarbons, JEE Main Notes JEE Notes | EduRev       
Order of heat of hydrogenation: 1-Butene> cis-2-Butene > trans-2-Butene
Order of stability: 1-Butene> cis-2-Butene > trans-2-Butene

Preparation of Alkenes:
1. Cracking of petroleum:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
2. Dehydrohalogenation of alkyl halides:   RCH2CH2X + alc.KOH → RCH = CH2
3. Dehydration of Alcohols:
Saytzeff Rule: In dehydration and dehydrohalogenation the preferential order for removal of an H is 3° > 2° > 1°
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
 4. Reduction of alkynes:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Chemical Properties:
1. Electrophilic Polar Addition Reactions

Reagent
Product
Name
Structure
Name
Structure
Halogens
(Cl2, Br2 only)
X:X
Ethylene dihalide
CH2XCH2X
Hydrohalic acids
H:X
Ethyl halide
CH3CH2X
 
Hypohalous acids
 
X:OH
 
Ethylene halohydrin
 
CH2XCH2OH
 
Sulfuric acid (cold)
 
H:OSO2OH
 
Ethyl bisulfate
 
CH3CH2OSO3H
 
Water (dil. H3O+)
 
H:OH
 
Ethyl alcohol
 
CH3CH2OH
Borane
 
H2B:H
Ethyl borane
(CH3CH2BH2) → (CH3CH2)3B
Peroxyformic acid
 
     H:O-OCH=O    
(HCO3H)
Ethylene glycol
CH2OHCH2OH


2. Addition of Hydrogen Halides to Alkenes: Markovnikov’s Addition:
R - CH = CH2 + HBr → R – CHBr – CH3
Mechanism:
R - CH = CH2 + HBr → R – CH+ - CH +Br-
R – CH+ - CH3 + Br- → R – CHBr - CH3
Anit- Markovnikov’s Addition (Peroxide Effect):
R - CH = CH2 + HBr + (C6H5CO)2O2 → R – CHBr – CH3
Mechanism
Initiation:
R - O - O - R  →  2RO
RO. +  HBr  →  Br.   +   ROH
Propagation
CH3CH = CH2   + Br →   CH3•CH - CH2Br
CH3CHCH2Br + HBr→ CH3CH2CH2Br + Br
Termination:
2RO  →  R - O - O - R  
Br + Br→Br2


3. Addition of Water to Alkenes: Acid Catalyzed Hydration:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


4. Oxymercuration-Demercuration:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
Examples:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


5. Hydroboration-Oxidation:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
Examples:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


6. Halogen Addition in Non-polar Solvent:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


7. Halogen Addition in Aqueous Medium:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


8. Syn – Hydroxylation: Formation of di-oles.
Hydrocarbons, JEE Main Notes JEE Notes | EduRev


9. Ozonolysis of Alkenes:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev 

Alkyne

  • Saturated open chain hydrocarbon with general formula (CnH2n-2).
  • At least one -c≡c-  (triple bond) group i.e. sp hybridisation, is present throughout the chain.
  • Physical properties of alkynes are similar to those of the corresponding  alkenes

Preparation
1. Dehydrohalogenation of vic-Dihalides or gem-Dihalides
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

2. Dehalogenation of vic-Tetrahalogen Compounds
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

3. Alkyl Substitution in Acetylene; Acidity of º C-H
 Hydrocarbons, JEE Main Notes JEE Notes | EduRev

4. From Calcium Carbide:
CaC2 +2H2O →   Ca(OH)2+ C2H2

5. Kolbe’s Electrolysis:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Chemical Properties
1. Hydrogenation: RC ≡ CCH2CH3 + 2H2 →  CH3CH2CH2CH2CH3
2. Hydro-halogenation:
Markovnikov addition: RC≡CH +HBr → RCBr=CH2 +HBr→ RCBr2-CH3
Anti-markovnikov addition: RC≡CH +HBr +peroxide → RCH=CHBr
Hydrocarbons, JEE Main Notes JEE Notes | EduRev  

Aromatic Hydrocarbons: 
For being aromatic a hydrocarbon should

  • be a cyclic compounds.
  • have planarity in geometry.  
  • have complete delocalization of electrons over ring.
  • follow Huckel Rule i.e. number of ?? electrons in ring = (4n+2).
    Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Benzene (C6H6)
1. Structure:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev
2. Chemical Reactions of Benzene:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

Anti-aromatic Hydrocarbons:
Highly unstable compounds.
Number of π electrons in ring = 4n.
Example:
Hydrocarbons, JEE Main Notes JEE Notes | EduRev

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