(a) Why are alkenes called unsaturated hydrocarbons?
(b) How will you test the presence of double bond in an alkene?
(c) Name the products formed when propene is subjected to ozonolysis.
(a) Alkenes contain two hydrogen atoms less than alkanes and thus they contain C—C double bond (C=C) in their molecule. Thus they are called unsaturated hydrocarbons.
(b) Alkenes react with cold dilute KMn04 solution to form gycols. Since bright purple colour of KMn04 disappears during the reaction it is used as a test for the presence of double bond.
(c) A mixture of acetaldehyde and formaldehyde is formed.
In the alkane, CH3CH2—C(CH3)2—CH2—CH(CH3)2, identify 1 °, 2 °, 3 ° carbon atoms and give the number of H-atoms bonded to each one of these.
Nucleophiles and electrophiles are reaction intermediates having electron rich and electron deficient centres respectively. Hence, they tend to attack electron deficient and electron rich centres respectively. Classify the following species as electrophiles and nucleophiles.
The relative reactivity of 1 °, 2 ° and 3 ° hydrogens towards chlorination is 1: 3.8 : 5. Calculate the percentages of all monochlorinated products obtained from 2-methylbutane.
Which of the following are correct?
(a) CH3 – O – CH+2 is more stable than CH3 – CH+2
(b) (CH3)2CH+ is less stable than CH3 – CH2 – CH+2
(c) CH2 = CH – CH+2 is more stable than CH3 – CH2 – CH+2
(d) CH2 = CH+ is more stable than CH3 – CH+2
For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated:
(a) C4H8 (one double bond) (b) C5H8 (one triple bond)
Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?
The molecules having dipole moment are________ .
(a) 2,2-Dimethylpropane
(b) trans-Pent-2-ene
(c) cw-Hex-3-ene
(d) 2,2,3,3-Tetramethylbutane
Write the IUPAC names of the following compounds.
(i) (CH3)CCH2C(CH3)3 (ii) (CH3)2C(C2H5)2
Explain the term aromaticity. What are the necessary conditions for any compound to show aromaticity?
Arrange the following: HCl, HBr, HI, HF in order of decreasing reactivity towards alkenes.
How will you demonstrate that double bonds of benzene are somewhat different from that of olefins?
Draw the cis- and trans-structures for hex-2-ene. Which iosmer will have higher b.p. and why?
In an electrophilic substitution reaction of nitrobenzene, the presence of nitro group ________ ‘
(a) deactivates the ring by inductive effect
(b) activates the ring by inductive effect
(c) decreases the charge density at ortho- and para-positions of the ring relative to meta-position by resonance
(d) increases the charge density at meta-position relative to the ortho and para-positions of the ring by resonance
Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will butene formed on the reduction of but-2-yne show geometrical isomerism?
Draw Newman and Sawhorse projections for the eclipsed and staggered conformations of ethane. Which of these conformations is more stable and why? .
An alkene ‘A’ on ozonolysis gives a mixture of ethanal and pentan-3-one. Write the structure and IUPAC name of ‘A’.
Propanal and pentan-3-ene are the ozonolysis products of an alkene. What is the structural formula of the alkene?
Write down the products ofozonolysis ofl, 2-dimethylbenzene (o-xylene). How does the result support Kekule structure of benzene?
Suggest the name of another Lewis acid instead of anhydrous aluminium chloride which can be used during ethylation of benzene.
For an electrophilic substitution reaction, the presence of a halogen atom in the benzene ring ;
(a) deactivates the ring by inductive effect
(b) deactivates the ring by resonance
(c) increases the charge density at ortho and para-positions relative to meta-position by resonance
(d) directs the incoming electrophile to meta-position by increasing the
charge density relative to ortho and para-positions. ‘
Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?
What happens when benzene is treated with excess of Cl2 in presence of sunlight? Give chemical reaction.
(a) Why are alkenes called unsaturated hydrocarbons?
(b) How will you test the presence of double bond in an alkene?
(c) Name the products formed when propene is subjected to ozonolysis.
An alkene ‘A’ contains three C—C, eight C—H, a-bonds, and one C—C n-bond. ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write the IUPAC name of’A’.
Discuss the preparation of alkanes by Wurtz reaction. What is the limitaHon of the reaction?
