MECHANISMS II Final2009 (200points)Name
1) (1+5+10=16pts) What is a free radical species?
ii) List 5 types of reactions that radicals can perform.
iii) provide an example of each reaction type.
2) (12pts) Draw a correct Lewis structure for the following molecules, and also draw the expected radicals produced when they are heated:
a) tBuOOH
b) (PhCO2)2
c) CH3CH2ONO
d) C6H11OCl
3) (2+3+9=14pts) i) Name a gas commonly used as an inert atmosphere for radical reactions.
ii) Oxygen, (O2) interferes with radical reactions. Draw two resonancestructures for O2(one of which is a diradical).
iii) Ethers are very useful organic solvents, but some ethers have a tendency to oxidize into unstable products if they are exposed to air over many months.
n-Butyl ether undergoes oxidation in air to yield the below hydroperoxide.
-Write a mechanism for this chain process.
4) Draw a Lewis structure of a radical species that you believe would have an unusually high stability, and a significantly long lifetime. (4pts)
b) What scientific proof do we have that radicals exist? (2pts)
c) (2+6=8pts) Radicals can undergo cyclization reactions to generate new ring systems, and there are two fundamental types (or modes) of cyclization.
-Name these two types of ring closure.
-Briefly explain how you classify or identify these two different processes.
5) (12pts) Identify 8 of these Mass Spectrometry related abbreviation:
APCI
QQQ
MALDI
GCMS
HPLC
ESI
HRMS
TOF
(MS)2
AMU
M/Z
FAB
6) (10+10=20pts) For each of the following molecules:
i) state their lowest energy photochemical excitation. e.g. X →Y*
ii) indicate which electron would most easily be removed by Electron Ionization.
7) (5pts) a) Label each of these three states as TRIPLET or SINGLET.
ii) Indicate for above, which is the highest energy state,
lowest energy.
b) (10pts)A section of the molecular orbital diagram for acetone is shown below.
i) Draw in box A the electrons after an allowed n→π* transition.
ii) Draw in box B the electrons after an allowedπ→π* transition.
iii) Which transition would you predict to have the larger absorption constant (ε) ?
iv) Which transition could be accomplished with the longest wavelength of irradiation ?
v) Which transition requires overall the least energy ?
8) (7pts) Write the mechanism for the interaction of a free radical initiator, tributyl tin hydride and alkyl bromide, which results in the formation of the corresponding alkyl radical.
Questions (9-15)
Write mechanisms for 6 of the following 7 transformations
(6 x 15 = 90)
Note that partial credit will be awarded for:
i) correct labeling of atoms in the starting materials and products
ii) correct initiation steps (where applicable)
ii) correct progress within a plausible mechanism.
9) Write the mechanism for this reaction, including how the rearranged product is formed. (15pts)
10) Write the mechanism for the following reaction. (15pts)
11) Bearing in mind that C=12 and H=1, write the mechanism for, and explain the following EI positive ion mass spectrum for BUTANE. (15pts)
12) Write the mechanism for the following reaction. (15pts)
13) Write the mechanism for the following reaction. (15pts)
14) Write a mechanism for the following reaction which generates 6 components. (15pts)
15) Write the mechanism for the following reaction (which requires photochemical initiation, and significantly slows down in the presence of free radical inhibitors). (15pts)
2009-MechII-Final1