Chem 207 Midterm 1
(A)
30.04.2010
Name___________________________________
Student Number__________________________
1) An oxygen atom has __________ valence electrons.
2) Draw a correct Lewis structure for boric acid, B(OH)3.
3) Covalent bonds may be polar or nonpolar. What property of the atoms forming a given bond determines
this?
4) Which of the following choices represent(s) a pair of resonance forms?
A)
B)
C)
D) both A and C
E) both B and C
5) The Lewis structure of trimethylamine is shown below. Draw the condensed structural formula which
corresponds to this Lewis structure.
6) Draw an acceptable line-angle formula for cyclobutanol (shown below).
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7) Draw a correct Lewis structure for acetaldehyde, CH3CHO.
8) Consider the set of compounds, NH3, HF, and H2O. Rank these compounds in order of increasing acidity
and discuss your rationale.
9) Would you predict trifluoromethanesulfonic acid, CF3SO3H, to be a stronger or weaker acid than
methanesulfonic acid, CH3SO3H? Explain your reasoning.
10) Which of the following terms comes closest to describing an electrophile?
A) Lewis base
B) anion
C) nucleophile
D) Lewis acid
E) nonpolar
10) ______
11) Consider the species CH3O-, NH2-, and CH3COO-. Rank these ions in order of increasing basicity, and
explain your rationale.
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12) When methanol (CH3OH) acts as a base, its conjugate acid is __________.
A) CH4O+
12) ______
B) -CH2OH
C) CH3OH2+
D) CH3OE) CH4OH
13) Draw the important resonance forms of:
14) One or more of the atoms in the structure shown should have nonzero formal charges. Redraw the structure
and indicate any such charges.
15) What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in
the manner indicated?
16) What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in
the manner indicated?
17) The CCO bond angle in acetone (CH3COCH3) is __________.
18) Choose the correct hybridization for the atom indicated in the molecule below.
A) sp
C) sp2
17) _____________
18) ______
B) sp3
D) none of the above
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19) Which of the molecules below is an ester?
A) CH3COOCH3
19) ______
B) CH3COOH
C) CH3CH2CH(CH3)2
D) HC≡CCH3
E) CH3OCH2CH2CH3
20) Which of the molecules below has the higher boiling point? Briefly explain your choice.
CH3CH2CH2OH
or
CH3CH2OCH3
21) Which of the molecules below has the higher boiling point? Briefly explain your choice.
CH3CH2CH2CH2CH3
or
(CH3)2CHCH2CH3
22) Which compound is more soluble in water? Briefly explain your choice.
CH3OCH3
or
CH3CH2OH
23) What type of intermolecular force results from the attraction of coordinated temporary dipoles induced in
adjacent molecules?
24) Draw the three-dimensional structure of chloroform (CHCl3) and show the direction of the molecular dipole
moment.
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25) What hybrid atomic orbitals are overlapping to form the carbon-oxygen s bond in
acetaldehyde (CH3CHO)? Draw a bonding diagram showing the hybridization of each
25) _____________
overlapping orbital making a bond and indicate the type of each bond.
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1) 6
2)
or
3) Electronegativity
4) E
5) (CH3)3N
6)
7)
8) NH3 < H2O < HF
When determining relative acidity, it is often useful to look at the relative basicity of the conjugate bases. The
stronger the acid, the weaker (more stable, less reactive) the conjugate base. In this case, one would look at the
relative basicity of F-, OH-, and NH2-. The relative strengths of these species can be gauged based on the
electronegativity of the charged atom in each. Since fluorine is the most electronegative, F- is the most stable, least
reactive base in the group. This means that its conjugate acid, HF, is the strongest.
9) Trifluoromethanesulfonic acid is a stronger acid. Compare the strengths of the conjugate bases and remember that
the weaker the base, the stronger the conjugate acid. Both bases are stabilized by resonance, but in the case of the
trifluoro derivative, the presence of the highly electronegative fluorine atoms serves to delocalize the negative
charge to an even greater extent. This additional delocalization makes trifluoromethanesulfonate a weaker base.
10) D
11) CH3COO- < CH3O- < NH2The first factor to consider is the nature of the atom which bears the negative charge. The more electronegative the
atom that bears the negative charge, the more stable the anion. Stable anions are less reactive and are hence weaker
bases. Since O is more electronegative than N, the NH2- is the strongest base in the set. In the remaining two
species, the negative charge is on the O, but in the case of CH3COO-, the negative charge is also delocalized by
resonance.
12) C
13)
14)
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15) σ
16) σ*
17) approximately 120°
18) C
19) A
20) CH3CH2CH2OH has the higher boiling point since it is capable of intermolecular hydrogen bonding.
21) CH3CH2CH2CH2CH3 has the higher boiling point. As the degree of branching increases, the surface area of the
molecule decreases and the potential for intermolecular attraction via London forces decreases. Greater surface area
leads to a more intermolecular attraction which in results in a higher boiling point.
22) CH3CH2OH is more soluble in water since it can donate a hydrogen bond to water and accept a hydrogen bond
from water. CH3OCH3 can only accept a hydrogen bond from water; it does not have hydrogen which can
hydrogen bond to water.
23) London dispersion forces
24)
25) carbon sp2 and oxygen sp2
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