RADICALS Spring 2014
FINAL (75+75 = 150pts)
Name
1) (10pts) Define these terms:
-FREE RADICAL
-FREE RADICAL INITIATOR
-FREE RADICAL INHIBITOR
-CHROMOPHORE
-HUND’S RULE (of Maximum Multiplicity)
2) Provide a chemical reaction that supports the idea that carbon radicals are planar (or
very shallow pyramidal structures that easily undergo inversion). (5pts)
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3) Draw a correct Lewis structure for the following molecules (INCLUDE ALL LONE
PAIRS), and also draw the expected radicals produced when they are heated (arrows not
needed). (12pts)
a) tBuOOH
b) (PhCO2)2
c) CN(CH3)2C-N=N-C(CH3)2CN
d) CFBrICl
4) Photochemistry is dominated by two main rules. (One deals with the geometries of
ground and excited states – the other deals with electron spin inversion upon excitation).
State these two rules. (4pts)
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5) (10pts) It is possible for the below radical to cyclize via intramolecular addition, to
produce either a 5 membered ring, and/or, a 6 membered ring.
i) draw mechanisms for both modes of cyclization
ii) label each cyclization as either exo or endo.
iii) in the above case, which process leads to a more stable radical ?
iv) How many sp2 hybridized Carbon atoms are present in the middle radical species ?
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6) (14pts) a) Label each of these three states as TRIPLET or SINGLET.
b) Indicate for above, which is the
-highest energy state,
-lowest energy,
-the most likely initial excited state.
c) For each photochemical transition listed below, provide a molecule which would
undergo such a transition as its lowest energy excitation.
π →π*
σ →σ*
n →π*
n →σ*
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7) (10+10pts) Draw in the arrows for the following two mechanisms.
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“EASIER” PROBLEMS
A-D) Attempt 3 of the following 4 questions.
(3 x 15 = 45)
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.
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A) Write a plausible mechanism (INITIATION and PROPAGATION steps) for the
following chain reaction.
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B) Provide two differences between SN1 and SRN1 reactions.
Write a plausible mechanism for the following SRN1 reaction.
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C) Write a plausible mechanism (INITIATION and PROPAGATION steps) for the
following chain reaction.
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D) Provide a mechanism for this reaction which was the first ever reported 1,2 radical
shift (rearrangement).
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“LESS EASY” PROBLEMS
(I-IV) Attempt 2 of the following 4 questions.
(2 x 15 = 30)
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.
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I) Explain what is happening in this triene isomerization, where the ketone is initially
excited via n→π* transition.
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II) Write a plausible mechanism for the following chain reaction of this Barton Ester type
of molecule, which includes a radical epoxide ring opening.
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III) Provide a mechanism for the following reaction, using the following guide:
Protonation on the Nitrogen (giving intermediate A), is followed by homolytic
(photochemical) cleavage of the N-Cl bond.
This produces a Nitrogen centered radical (intermediate B), which abstracts a Hydrogen
atom intramolecularly, producing a Carbon centered radical.
Then, this radical abstracts a Chlorine atom from another equivalent of intermediate A,
to generate another equivalent of intermediate B (it’s a chain process), but also more
importantly, it generates the protonated form of a secondary amine which has a
Chloroalkyl substituent (intermediate C).
When the base is added, the protonated amine (intermediate C) is deprotonated, and the
thus generated neutral Nitrogen is now nucleophilic. It performs an intramolecular SN2
attack (Chloride is the leaving group).
This cyclization makes the Nitrogen positive, and another equivalent of base
deprotonates the Nitrogen, yielding the final product.
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IV) Write a plausible mechanism for the following photochemical transformation,
including how the ketone product initially produced, undergoes further photochemical
reaction.
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