Answers to 2.8 Exercises
2.8 Exercise 1
1.
2.
i)
ii)
iii)
a)
break a covalent bond in such a way that one electron goes to each atom
a species with an unpaired electron
replacement of one atom or group atoms by another
initiation
Cl.
Cl
Cl
Cl.
+
propagation
Cl.
H
H
H
C
C
H
H
H
H
Cl
+
H
H
.C
C
H
H
H
propagation
Cl
Cl
H
H
.C
C
H
H
Cl
H
H
H
C
C
H
H
H
Cl.
+
termination
Cl.
b)
Cl.
Cl
Cl
i)
Cl.
Cl
H
Cl
H
H
C
C
Cl
H
H
H
.C
C
Cl
H
H
H
Cl
H
Cl
H
H
.C
C
Cl
H
H
+
Cl.
H
H
H
H
C
C
C
C
H
H
H
H
+
H
H
C
C
Cl
H
H
ii)
H
H
H
C
H
H
H
C.
.C
C
H
H
H
H
H
H
2.8 Exercise 2
1.
a)
Cl
F
C
Cl
F
b)
Cl
Cl
F
C
Cl
F
Cl.
+
F
F
2.
C.
a)
The halogen is more electronegative than carbon
so the C-X bond is polar
so the carbon atom has a partial positive charge
to which the lone pair of electrons on a nucleophile can be attracted
b)
i)
C2H5Br + NaOH  C2H5OH + NaBr
H
CH3
HO:
ii)
H
Br
C
CH3
H
OH
+
Br-
CN
+
Br-
H
CH3CHClCH3 + KCN  CH3CH(CN)CH3
CH3
CH3
NC:
iii)
C
CH3
Cl
C
CH3
H
C
H
C2H5CH2CH2I + 2NH3  C2H5CH2CH2NH2 + NH4I
H
C2H5CH2
H3N:
C
I
C2H5CH2
H
H
H
C
N
H
H3N:
+
H
H
C2H5CH2
H
+
I
H
N
C
-
H
H
+
NH4+
+
I
3.
nucleophilic substitution
H
C
C2H5CH2
-
H
Cl
C2H5CH2
C
H
HO:
OH
H
hydroxide ion is a nucleophile
aqueous conditions
warm
elimination
HO:
C2H5
H
H
C
C
H
H
C2H5
C
Cl
H
H
+
C
Cl-
+
H2O
H
hydroxide ion is a base
ethanolic conditions
heat
4.
iodoethane reacts fastest, followed by bromoethane and then chloroethane
the C-X bond needs to be broken during the reaction
I is a larger atom than Br or Cl, so the C-I bond is longer than C-Br or C-Cl
Hence the C-I bond is weaker than C-Br or C-Cl
So it requires least energy to break and is broken more quickly
5.
a)
b)
but-1-ene only
but-1-ene and but-2-ene
H
H
H
H
1
3
C H
C
C
H C
H
Br
the H atom can be lost from C1 or C3
If H is lost from C1 but-1-ene will be formed
If H is lost from C3 but-2-ene will be formed
methylpropene only
methylpropene only
H
c)
d)
H