Alkane
Conformations of Alkane
Preparation of Alkanes:
Chemical Properties of Alkane
Alkene (olefins)
Geometric Isomers:
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
Heats of Hydrogenation: Heat of hydrogenation increases with increase in stability of alkene.
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:
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°
4. Reduction of alkynes:
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+ - CH3 +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
CH3•CHCH2Br + HBr→ CH3CH2CH2Br + Br•
Termination:
2RO• → R - O - O - R
Br• + Br•→Br2
3. Addition of Water to Alkenes: Acid Catalyzed Hydration:
4. Oxymercuration-Demercuration:
Examples:
5. Hydroboration-Oxidation:
Examples:
6. Halogen Addition in Non-polar Solvent:
7. Halogen Addition in Aqueous Medium:
8. Syn – Hydroxylation: Formation of di-oles.
9. Ozonolysis of Alkenes:
Alkyne
Preparation
1. Dehydrohalogenation of vic-Dihalides or gem-Dihalides
2. Dehalogenation of vic-Tetrahalogen Compounds
3. Alkyl Substitution in Acetylene; Acidity of º C-H
4. From Calcium Carbide:
CaC2 +2H2O → Ca(OH)2+ C2H2
5. Kolbe’s Electrolysis:
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
Aromatic Hydrocarbons:
For being aromatic a hydrocarbon should
Benzene (C6H6)
1. Structure:
2. Chemical Reactions of Benzene:
Anti-aromatic Hydrocarbons:
Highly unstable compounds.
Number of π electrons in ring = 4n.
Example:
1. What are hydrocarbons? |
2. How are hydrocarbons classified? |
3. What are the common uses of hydrocarbons? |
4. How are hydrocarbons extracted from the Earth? |
5. Are hydrocarbons harmful to the environment? |
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