Chapter 9 - University of Dayton Academic Webserver

328
Chapter 9: Molecular Structures
Cl
Cl
102. (a) The Lewis structures for the three isomers of C 6 H 6 O 2 (each with one benzene ring and two –OH
H
H
groups attached) look like this:
C
C
. . .
O
C
C
H
(i)
H
C
C
. . .
O
H
H
H
H
C
C
. . .
O
C
C
H
(ii)
(b) All of these molecules have the same kind and strength of hydrogen bonding; however, because of
the proximity of the two –OH groups in structure (i), these molecules are able to experience
intramolecular hydrogen bonding (that is hydrogen bonding between H atoms and O atoms within
the same molecule). Less hydrogen bonding disruption will be experienced when the molecules
undergo a transition to the liquid state; hence, (i) will melt at a lower temperature than the other two.
The asymmetry of structure (ii) might suggest that the intermolecular forces could be a little bit
weaker in the solid, compared to those experienced among the higher-symmetry molecules in
structure (iii). Therefore, the predicted order of for melting points of these three solids would be (i) <
(ii) > (iii).
H
C
C
H
. . .
103. (a) Halomethane, CHBrClCF 3 (44 e – ) has the following Lewis Structure.
.
.
. . .
H
Br C C F
. Cl . .
.
. .
.
. F .
. F.
.
.
(b) As a asymmetric molecule with polar bonds, Halomethane is a polar structure.
O
H
. . . .
.
.
H
H
C
C
. O
. .
C
C
. O.
.
(iii)
H
H
C
C
H
H