Propose mechanisms to explain the opposite regiochemistry observed in the following two reactions.

Suggest a synthetic scheme, involving a protecting group, to generate the molecule shown starting with the molecule at the left.

(a)

a. Propose a mechanism for the following reaction.

2 (CH₃)₂C=CH–CH₃ + cat. H⁺ → 2,3,4,4-tetramethylhex-2-ene

b. Show the first three steps (as far as the tetramer) in the BF₃–catalyzed polymerization of propylene to form polypropylene.

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.

(a) 3-methylnon-4-yn-3-ol (“3-ol” means there is an OH group on C3.)

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.

(b) cis-1-ethyl-2-methylcyclopropane

Show how you would accomplish the following synthetic conversions.

(c) 2−methylcyclohexanol → 1−bromo−1−methylcyclohexane

Work backward to show how the cyclopropane would be synthesized from the chloroalkane shown.

For each of the following target molecules, design a multistep synthesis to show how it can be prepared from the given starting material:

b.

Identify A–E.