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Basic Organic Chemistry
Homework 1
Basic Principles
Answer Key
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Basic Organic Chemistry
Homework Sheet One - Basic Principles
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Q1: Assign formal charges (on the atoms that require
them) to the following molecules and ions. All lone
pairs are shown already.
a)
b) H3C
H2C CH
e)
O
N
f)
O
c)
Se
H
O
H
H3N C
H
d)
a)
C
C
O
H
g)
N
O
N
b)
h)
k)
O
F
S
N
O
F
F
B
O
amines
H
Br
Br
H
CH
H
H
H
H
H
Br
H
Br
C C
H
C C
H
a)
_H
H3C
H
C C
H
H
a)
H3C—Br
Et2C=O
O
b)
imines
unbranched
C
N
cyclic
Q5: Use the δ+ / δ- convention to indicate the direction of polarity for each
of the bonds indicated by lines (— or =).
Also, state whether the molecule is polar or non-polar overall.
e)
Q6: a) Draw (in
skeletal form) the
resonance
structures (if any)
for the four
anions shown,
using curly
arrows to show
the movement of
the π electron
pair.
O
O
C C
C C
C
H2C
f)
c)
Q3: Put these molecules in order of increasing dipole
moment (polarity), drawing each as a skeletal structure.
H
Q4: Draw skeletal structures of all the
isomers of C3H7N (there are at least 11).
Classifying each structure as an amine or
imine and as unbranched or cyclic. Then
draw out the following table and place each
structure in its correct box.
N
N H
H
l)
N
N H
O
C
H
e)
H
j) H
N
d)
C
H
H2C P(CH3)3
H3C N
Br
CH2
H2N
O
O
i)
Q2: Determine the bonding hybridisation
for every p-block atom present in each of
the following species:
b)
H3C—Li
c)
f)
g)
d)
H3C—OMe
H3C—CH3
F—CH3
Cl3C—Cl
h)
H3C—MgBr
7) Each of the four compounds below can lose its NH proton to
produce an organic anion.
_
N
H
N
O
O
S
S
O O
O O
_
c)
N
O
S
O O
d)
H
N+
NH2
N
O
H
H
N
H
N
O
S
O O
a) By considering resonance, decide which compound produces the
most stable anion.
b) Which produces the least stable anion?
c) Hence, put the four nitrogen compounds above in order of
increasing acidity
(80 marks)
1
Q1: Assign formal charges, where required to the following
molecules and ions. All lone pairs are shown already.
_
a)
b)
c)
d)
H3C
H2C CH
e)
Se
H
f)
+O
O
H
H3N C
H
H
g)_
N_
O
H
j)
i)
+
N
h)
+
H2C_ P(CH3)3
N
H
_
O
F
_B F
+O
F
l)
N
N+
O _
+
O
_
_
k)
N
H3C N
C
C+
O
_
+
O
O
S
(12 marks)
Q2: Determine the bonding hybridisation for every p-block atom
present in each of the following species:
a)
sp2
sp3
H2N 3
CH2
d)
sp2
sp2
O
C 2
H sp
sp
sp2
N H
sp2
sp3
C
H
sp2 sp2
b)
N
sp2
sp2
sp2
c)
sp3
sp3
sp3
e)
H2C
N H
H
f)
sp2
sp2
sp2
sp3
O
C
sp
sp3
sp2
sp3
sp2
sp2
O
sp3
sp3
CH
sp2
C
sp
N
sp
(12 marks)
2
Q3: Put these molecules in order of increasing dipole moment
(polarity), drawing each as a skeletal structure.
Br
H
Br
Br
H
C C
H
Non polar
µ= 0
H2C
H
H
C C
Br
H
C C
H
H
Slightly asymmetrical
distribution of
electron density
H3C
H
C C
H
H
H
C C
H
H
Br
Electronegative Br pulls electron
density to one side of the molecule
Br
CH2
Br
Br
Br
increasing
polarity
Br
(5 marks)
Q4: Draw skeletal structures of all the isomers of C3H7N (there are at
least 11). Classifying each structure as an amine or imine and as
unbranched or cyclic. Then draw out the following table and place
each structure in its correct box.
amines
imines
NH 2
NH 2
NH
N
N
unbranched
HN
H 2N
NH 2
cyclic
(saturated)
NH
N
N
not possible from
empirical formula
(11 marks –
1 for each
compound)
3
Q5: Use the δ+ / δ- convention to indicate the direction of polarity
for each of the bonds indicated by a line (—).
Also, state whether the molecule is polar or non-polar overall.
a) δ+ δH3C—Br
b)
δ+
δ-
Et2C=O
polar molecule
δ+
polar molecule
polar molecule
e)
δ-
H3C—Li
f)
No bond polarity
H3C—CH3
NON-polar molecule
c)
δ+
δ-
H3C—OMe
polar molecule
g)
δ-
δ+
F—CH3
polar molecule
d) δ+ δCl3C—Cl
NON-polar molecule
h) δ- δ+
H3C—MgBr
polar molecule
(8 marks)
Q6: a) Draw (in skeletal form) the resonance structures (if any) for
the four anions shown, using curly arrows to show the movement of
the π electron pair.
H_
O
_
N
_
O
S
N
O O
H
+N
NH2
(4 x 3 marks)
4
Q6: a) Draw (in skeletal form) the resonance structures (if any) for
the four anions shown.
_
H
H
O
O_
_
N
No π-bonds ⇒ no resonance stabilisation
_
O
S
_O
N
O O
S
N
O
H
H
N
NH2
N
O O_
O O
+N
S
+
NH2
(4 x 3 marks)
O
S
O O
H
N
S
O
N
O O
H
N
H
H
N
O
S
O O
O
7) Each of the four compounds above can lose its NH proton to
produce an organic anion. a) Which compound produces the most
stable anion? b) Which produces the least stable anion?
c) Hence, put the four nitrogen compounds above in order of
increasing acidity
N
H
N
O
H
O
amine
pKa = 35
(least acidic)
(least stable;
not at
all resonance
stabilised)
S
H
N
O O
amide
pKa = 28
sulphonamide
pKa = 12
(conjugate base
has 2 resonance
forms)
(conjugate base
has 3 resonance
forms)
O
S
O O
H
N
S
O
O O
bis-sulphonamide
pKa = 10
(most acidic)
(most stable;
has 5 resonance
forms)
(3 + 3 + 4 marks, Total: 80 marks)
5