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Compounds of carbon and hydrogen.
Classification of Hydrocarbons:
Open chain saturated hydrocarbon with general formula (CnH2n+2).
All the C atoms are single bonded i.e. sp3 hybridised.
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.
Staggered Conformation: H atoms on two adjacent carbon atoms are farthest to each other i.e. dihedral angle is 60.
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:
?
Hydrogenation of Alkenes:
Wurtz Reaction:
2RX + 2Na → R-R + 2NaX
2Na + 2CH3CH2CH2Cl → CH3CH2CH2CH2-CH2CH3 + 2NaCl
Corey House Reaction:
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
Direct Halogenation
RH + X2→ RX + HX
Order of Reactivity of X2: F2 > Cl2 > Br2; I2 does not react
?a. Initiation Step
Cl-Cl 2Cl.
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 HNO3 at about 400oC to give nitroalkanes.
¨This is also known as vapour phase nitration.
Combustion:
?Alkanes burn readily with non luminous flame in presence of air or oxygen to give CO2 & water along with evolution of heat.
C2H6 + 7O2 → 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.
Oxidization of 30 alkane:?
Tertiary alkanes are oxidized to tertiary alcoholsby KMnO4
R3CH + KMnO4 → R3COH
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.
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
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 ofan H is 3° > 2° > 1°
4. Reduction of alkynes:
1. Electrophilic Polar Addition Reactions
Reagent
Product
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:
(CH3CH2BH2)®(CH3CH2)3B
H:O - OCH = O
4. Oxymercuration-Demercuration:
Examples:
5. Hydroboration-Oxidation:
6. Halogen Addition in Non-polar Solvent:
7. Halogen Addition in Aqueous Medium:
8. Syn – Hydroxylation: Formation of di-oles.
9. Ozonolysis of Alkenes:
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
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:
1. Hydrogenation: RC ≡ CCH2CH3 + 2H2 → CH3CH2CH2CH2CH3
2. Hydro-halogenation:
Markovnikov addition: RC≡CH +HBr → RCBr=CH2 +HBr→ RCBr2-CH3
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). :
1. Structure:
2. Chemical Reactions of Benzene:
Highly unstable compounds.
Number of π electrons in ring = 4n.
Example:
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