BackEvidence for the concertedness of epoxide formation comes from the stereospecificity of the reaction. If step 2 of a hypothetical stepwise mechanism were slow enough to make the reaction non-concerted, how would the product distribution change?
One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.
(b) Concerted , actual mechanism (butterfly transition state:
What is the major product of the reaction of 2-methyl-2-butene with each of the following reagents?
f. MCPBA (a peroxyacid)
What alkene would you treat with a peroxyacid in order to obtain each of the epoxides in Problem 27?
c. 2,2,3,3-tetramethyloxirane
d. 2,3-epoxy-2-methylpentane
How does the carbonyl in mCPBA weaken the O―O σ bond (i.e., make a better leaving group)?
Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (v) mCPBA
(d)
Rank the reactivity of the following alkenes with mCPBA ( 1 = most reactive , 5 least reactive ).
Predict the product(s) when each of the following are reacted with mCPBA, making sure to indicate the relative stereochemical outcome. Indicate any racemic mixtures by drawing both enantiomers.
(d)
Limonene is one of the compounds that give lemons their tangy odor. Show the structures of the products expected when limonene reacts with an excess of each of these reagents.
b. m-chloroperoxybenzoic acid
Predict the products, including stereochemistry where appropriate, for the m-chloroperoxybenzoic acid epoxidations of the following alkenes.
c. cis-cyclodecene
d. trans-cyclodecene
Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (v) mCPBA;
(k)
One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.
(a) Stepwise, hypothetical mechanism:
Predict the product(s) of each of the following reactions, making sure to indicate the relative stereochemical outcome. Indicate any racemic mixtures by drawing both enantiomers.
(c)
a. What alkene is required to synthesize each of the following compounds?
b. What other epoxide is formed in each synthesis?
c. Assign an R or S configuration to each asymmetric center.
2.