Life Sciences 1a
Practice Problems 1
1. Draw the Lewis structure for: HCO3(McMurry pp. 114-123)
Also: What’s the molecular shape?
2. Show the direction of the dipole moment in each of the following bonds using the
provided electronegativity table. On which atom is most of the electron density?
(McMurry pp. 124-129):
(a)
H3C
Br
(b)
H3C
Li
3. Discuss whether the following statements are correct (explain):
(a) “When NaCl is dissolved in water, the water molecules closest to the ions will tend
to preferentially orient themselves so that their oxygen atoms face the sodium ions
and face away from the chloride ions.”
(Alberts, 2-4)
(b) “An ionic bond can, in principle, be thought of as a very polar covalent bond. Polar
covalent bonds, then, fall somewhere between ionic bonds at one end of the
spectrum and nonpolar covalent bonds at the other end.”
(Alberts, 2-3)
4. Draw a standard line bond structure for compounds of the following molecular
formulas:
(a) NH2CH2CH2OH
(b) CH3CN
(c) (C6H5)COOH
5. Provide a molecular formula for each of the following molecules. Describe the
geometry at the circled carbon atoms.
(a) vanillin
(b) estrogen
(c) cytosine
CH3
O
O
HO
NH2
N
OH
HO
O
H
HO
OH
N
O
6. Do each of the following sets of molecules depict enantiomers or different views of
the same molecule?
Me
(a)
Me
vs
OH
H2N
OH
H2N
O
O
(b)
vs
OH
H2N
HO
NH2
O
O
Me
(c)
Me
vs
OH
OH
HO
HO
(d)
H
H
O
OH
H
vs
H
H
OH
H
OH OH
O
7. Draw one possible wedge and dash structure of the molecule below, showing the
hydrogens at chiral centers.
O
HO
O
NH2
N
H
O
O
1.
O
H O
2.
C
H3C
(a)
O
Bonds can also be shown as lines
Shape of C is trigonal planar
Br
(b)
Br
H3C
Li
C
3.
For answers see Alberts page A:4
4.
(a) NH2CH2CH2OH
(b) CH3CN
(c) (C6H5)COOH
O
5.
OH
OH
H2N
N
(a) vanillin
(b) estrogen
CH3
O
O
N
O
H
HO
C8H8O 3
tetrahedral, trig planar
C18H24O 2
both tetrahedral
NH2
OH
HO
HO
6.
(c) cytosine
N
OH
C9H13N3O 4
tetrahedral,trig planar
(a) enantiomers
(b) same molecule
(c) same molecule
(d) enantiomers
7.
O H
HO
O
H2N H
N
H
O
O
O
This is one possibility-chiral carbons are circled