CHEM43-6311
assignment-3-sykes-ch3-lewis-structures-pkas.docx
2016January17
page 1
1. Show the Lewis structures of all important resonance forms for the following. Suggest the
relative energies of orbitals (including molecular orbitals) occupied by valence electrons within
each. Determine the hybridization of P, S, C, N, O, and B and explain what determines the
hybridization.
a.
b.
c.
d.
e.
f.
g.
h.
CH2P(CH3)3
BCl3
SO2
SO3
CH3NC
CO
NH2CONH2
CNO-
2. Order the following columns or rows of compounds according to pKa’s and explain the
order.
A
F
C
B
H
HC CH
R
H
O
OH
R
CH2
O
CH2
R
O
O
CH2
RO
O
E
O
ROH2
CH3CH2SH
D
CH3CN
R
RO
CH2
OR
NH3
O
+
J
NH+
CH3NO2
H2CO3
R
OH
NH4
OH
HCl
I
3. Which compound is more acidic? Explain all relevant effects: field, inductive, any other
effect?
+H3N
NH 3+
CO 2H
CO 2H
4. Show a derivation of an analytical expression that relates pKa to pKb and does not
depend on the concentration of any acid or base.
CHEM43-6311
assignment-3-sykes-ch3-lewis-structures-pkas.docx
2016January17
page 2
5. Estimate the pKa’s of the most acidic proton on following compounds and explain your
reasoning.
6. Show all resonance structures for the intermediate cation that is formed when benzene
is protonated.
7. Three isomeric cations are formed when furan is protonated. A) Show the three isomers
and all of their resonance structures. B) Which isomer is most stable and explain.
CHEM43-6311
assignment-3-sykes-ch3-lewis-structures-pkas.docx
2016January17
page 3
8. Explain why A is a stronger acid.
9. A) Show all tautomers (isomers where only the position of protons change) of the
following ketone. As for the ketone, no atom should have a formal charge. (Hint: this
ketone has two inequivalent isomers). B) Of the three isomers which is most stable and
explain.