School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
General Principles of Chemistry – CHEM120
Tutorial 11 – 23 and 25 October 2013
1. When light is shone on a mixture of chlorine and chloromethane, dichloromethane is one
of the products formed. Write the propagation steps that explain the formation of
dichloromethane from chloromethane under these conditions.
CH3Cl + Cl• → •CH2Cl + HCl
CH2Cl + Cl-Cl → CH2Cl2 + Cl•
2. Draw the major and minor products for the dehydration of 2-pentanol
OH
H2SO4
major product
minor product
3. Suggest suitable reagents for the following reactions:
(a)
H2, Pd / C
OH
(b)
H2SO4
H2O
(c)
C
H3C
C
CH3
H2
Lindlar's catalyst H C
3
(d)
Br2
in excess
C
C
CH3
H2
Linder's catalyst H C
3
CH3
CH3
4. Which of the following SN2 reactions is the fastest? Why?
(a) CH3CH2CH2I + HO- → CH3CH2CH2OH + I(b) CH3CH2CH2Br + HO- → CH3CH2CH2OH + Br(c) CH3CH2CH2I + H2O → CH3CH2CH2OH + HI
(d) CH3CHICH3 + HO- → CH3CH2CH2OH + IThe first reaction is fastest because it involves: a primary haloalkane; the better leaving
group (I- rather than Br-); the stronger nucleophile (HO- rather than H2O).
5. Give a detailed mechanism (using curl arrows) of the following reaction and give the
structure of all the products and intermediates of the reaction. Indicate which is the major
product and explain why this is the major product of the reaction.
mech 1
H
Cl-
Cl
H
H
mech 2
Cl
H
Transition state more stable
H
H
Cl
major product
Cl-
H
H
Transition state less stable
Cl
H
H
minor product
Markovnikov’s Rule :-“In the addition of HX to an alkene, the hydrogen adds to the carbon
atom of the double bond bearing the greater number of hydrogen atoms bonded directly to it.”