Alkenes - Conceptual Questions

1. What are alkenes?
2. Comment on the C=C bond length in ethane with respect to C-C bond length in ethane.
3. What is the IUPAC nomenclature systems for alkenes?
4. What is the IUPAC nomenclature with alkenes having two or more double bonds?
5. Discuss structural isomerism in alkenes.
6. Discuss geometrical isomerism in alkenes.
7. Geometrical isomers have different physical properties but simimar chemical properties. Write down how physical properties are different between cis and trans isomers of alkenes.
8. Explain E-Z system for geometrical isomers.
9. Comment on the stability of alkenes?
10. Explain the preparation of alkene for the following methods.

i. from alcohols.
ii. from alkyl halides
iii. from dihalogen derivatives
iv. from alkynes
v. by electrolysis of potassium salts of dicarboxylic acids (Kolbe reaction)

11. What are physical properties of alkenes?
a. Physical state and smell
b. melting points
c. Boiling points
d. Solubility in water
e. Dipole moments

12. Explain the following chemical properties of alkenes.

A. Addition reactions
a. Explain the reaction mechanism of electrophilic addition reactiosn of alkenes.

i. Addition of halogens
ii. Addition of of halogen acids
iii. Addition of water (hydration)
iv. Addition of hypohalous acid

B. Oxidation reactions
i. Combustion
ii. Hydroboration
iii. Oxidation of potassium permanganate
iv. Catalytic oxidation
v. Oxidation with ozone

C. Reduction

D. Polymerisation reactions
i. Polymerisation of ethane
ii. Polymerisation of vinyl chloride
iii. Polymerisation of styrene
iv. Polymerisation of tetrafluoroethylene

13. What are alkadienes? What is their relation to alkynes?
14. Explain the following terms:
a. conjugated dienes.
b. Isolated dienes
c. Cumulated diens or allenes.

15. Discuss stability of conjugated dienes.
16. Explain the concept of delocalisation of electrons in dienes.

17. Explain the following reactins of dienes
i. Electrophilic addition to conjugated dienes

Application Questions - 22 Alkenes

1. An alkene on treating with hot acidified KMnO4 gives 4-oxopentanoic acid. The alkene is
(a) pentene
(b) 2-pentene
(c) 1-methylcyclobutene
(d) 1,2-dimethylcyclopropene

2. The addition of Br2 to trans-2-butene produces
(a) (+)-2,3-dibromobutane
(b) (-)-2,3-dibromobutane
(c) rac-2,3-dibromobutane
(d) meso-2,3-dibromobutane

3. The treatment of propene with Cl-2 at 500-600 °C produces
(a) 1,2-dichloropropane
(b) allyl chloride
(c) 2,3-dichloropropene
(d) 1,3-dichloropropene

4. The electrophilic addition of 1,3-butadiene produces
(a) 1,2-addition product only
(b) 1,4-addition product
(c) both 1,2- and 1,4- addition products which are not at equilibrium with each other
(d) both 1,2- and 1,4-addition products which are at equilibrium with each other

Past JEE Questions Ch.22 Alkenes

1984

Baeyer's reagent is
a) alkaline potassium permanganate solution
b) acidified potassium permanganate solution
c) neutral potassium permanganate solution
d) acqueous bromine solution

1985.

anti-markonikov addition of HBr is not observed in
a) propene
b) butene
c) 2-butene
d) 2-pentene

1986
Dipole moment is shown by

a) 1,4 dichlorobenzene
b) cis-1,2-dichloroethene
c) trans-1,2-dichloroethene
d) 1,2-dichloro-2-pentene

Answer b and d

1987

4. of the following compounds, whihc will have a zero dipole moment

a) 1,1 dichloroethylene
b) cis-1,2-dichlorethylene
c) trans-1,2-dichloroethylene
d) none of these compounds

answer c

1991

5.1-chlorobutane on reaction with alcoholic potash gives
a) 1-butene
b) 1-butanol
c) 2-butene
d) 2-butanol

answer a

1992

6. The molecules that will have dipole moment are

a) 2,2-dimethylpropane
b) trans-2-pentene
c) cis-3-hexene
d) 2,2,3,3,-tetrametylbutane

answer b and c.

1993

Which of the following has the smallest heat of hydrogenation per mole?
a) 1-butene
b) trans-2-butene
c) cis-2-butene
d) 1,3-butadiene

answer d

1998
Which of the following compounds will show geometric isomerism?
a) 2-Butene
b) Propene
c) 1-Phenylpropene
d) 2-Methyl-2-butene

2000

Which of the following compounds will exhibit geometric isomerism?
a) 1-phenyl-2-butene
b) 3-phenyl-1-butene
c) 2-phenyl-1-butene
d) 1,1-Diphenyl-1-propene


JEE Question 2007 paper II

Cyclohexene on ozonolysis followed by reaction with zinc dust and water gives compound E. Compound E on further treatment with aqueous KOH yields compound F. Compound F is

Options given as pictures

IIT JEE Chemistry Questions 22. Alkenes

Preparation, properties and reactions of alkenes:

Physical properties: boiling points, density and dipole moments
Acidity; Acid catalysed hydration of alkenes(excluding the stereochemistry of addition and elimination);
Reactions of alkenes with KMnO4 and ozone;
Reduction of alkenes;
Preparation of alkenes by elimination reactions;
Electrophilic addition reactions of alkenes with X2, HX, HOX and H2O (X=halogen);
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1. About alkenes

1. What are alkenes?
2. What is the general formula of alkenes?
3. What is the simplest alkene?
4. What are the bonds in carbon-carbon double bonds (pi and sigma bonds)?
5. What is the carbon-carbon bond length ethene?

2. Nomenclature

3. Isomerism in alekenes

4. Stability of alkenes

5. Preparation of alkenes

1. How do you prepare alkenes from alcohols?
2. How do you prepare alkens from alkyl halides?
3. How do you prepare alkens from vicinal dihalides?
4. How do you prepare alkens from alkynes?
5. How do you prepare alkens from potassium salts of dicarboxylic acids?

6. Physical properties

1. Which alkenes are gases at room temperature?
2. Which alkenes are liquids at room temperature?
3. Which alkenes are solids at room temperature?
4. Compare melting points of alkenes with that of alkanes.
5. Compare melting points of trans-alkens with cis-alkenes.