Chemistry 301-301A - Hour Examination #3, December 11, 2003

“.....as we know, there are known unknowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know.” Donald Rumsfeld (winner of a British award given to the worst mangler of the English language in 2003)

“I know, a proof is a proof. What kind of a proof is a proof? A proof is a proof and when you have a good proof it's because it's proven." Jean Chrétien

(hon. mention for the same award)

1[18 points] (a) Acid-catalyzed addition of water to 3-methyl-1-butene (1) results in formation of large amounts of a rearranged alcohol (2), in addition to the expected alcohol (3). Explain, with excellent arrow formalisms.

H2O + H O+ 3 OH OH 1 3 2 (b) On the other hand hydroboration of 1, followed by oxidation, does not lead to any rearranged product. Only alcohol 4 is formed. Explain. Detailed mechanisms are not needed here, but a drawing of the transition state for the hydroboration step is.

1. BH3

OH 2. HOOH/HO – 1 4 (c) But there are some strange things that happen in hydroboration. For example when 2-methyl-2-butene (5) is hydroborated at high temperature, then treated with HOOH/HO–, alcohol 4 is still one of the products. Explain mechanistcally. Hint: at high temperature hydroboration is reversible.

1. BH3

OH 2. HOOH/HO – 5 4 2 [12 points]. Problem 1, part a showed the classical rearrangement typical of additions of HX. Explain why alkene 6 gives 7, but no rearranged product 8 when it is hydrated.

H2O

+ H3O OH HO 6 7 8

3 [20 points]. Fill in the unknowns in the following reactions starting from 1,3- butadiene. Mechanisms are not necessary.

1) X H (a) 2 CH =O + 2 H 2) Y O

Z (b) Cl + W

Br2 (Q and R are (c) Q + R not enantiomers)

B V (d) 4 [20 points]. Show how you would convert 1-butene into the following compounds. Mechanisms are not necessary, and you may start with any inorganic reagent, tert- butyl alcohol [(CH3)3COH], methyl alcohol (HOCH3), sodium methoxide (NaOCH3), snake oil, sulfuric acid (HOSO2OH), diazomethane (CH2N2), lizard oil, pyridine, gila monster oil, green, trifluoroperacetic acid (CF3CO3H), and Henry L. Gingrich’s secret recipe for squid and black bean sauce.

(a) (b)

??? Br Br

OH OCH 3

OCH OH 3 (c) (d) (e)

5 [18 points]. When alkenes are treated with trifluoroacetic acid, no epoxide (9) is formed (reaction 1). Trifluoroperacetic acid, however, effects the transformation efficiently (reaction 2). O H3C CH3 (1) F3C OH no 9 C8H13F3O2 H3C CH3 O

H C CH H C CH 3 3 3 3 F3C OOH (2) O

H3C CH3 H3C CH3

9 (a) What is the product in reaction (1)?

(b) Propose two mechanisms for reaction (2), one a single step process and the other a multi-step process.

(c) Propose an experiment that would distinguish between the two mechanisms. 6 [12 points]. When ethyl chloride is photochlorinated, two products, each C2H4Cl2 are possible.

Cl 2 CH 3CH 2Cl two C2H4Cl2 hn

(a) What are they?

(b) Which will be the major product and why? A mechanistic analysis is necessary here, so please write a mechanism. data:

(a) When the light (hn) is off, nothing happens.

(b) Nothing happens when the light shines on ethyl chloride alone.

“I pledge that I have not violated the Honour Code on this examination.”