Reactions and Synthesis

Dichlorocarbene can be generated by heating sodium trichloroacetate.

Propose a mechanism for the reaction, and use curved arrows to indicate

the movement of electrons in each step. What relationship does

your mechanism bear to the base-induced elimination of HCl from

chloroform?

The reaction of cyclohexene with mercury(II) acetate in CH₃OH rather than

H₂O, followed by treatment with NaBH₄, yields cyclohexyl methyl ether rather than cyclohexanol. Suggest a mechanism. 

Use your general knowledge of alkene chemistry to suggest a mechanism for the following reaction.

Predict the products of the following reactions (the aromatic ring is

unreactive in all cases). Indicate regiochemistry when relevant.

One problem with elimination reactions is that mixtures of products are often formed. For example, treatment of 2-bromo-2-methylbutane with KOH in ethanol yields a mixture of two alkene products. What are their likely structures?

How many alkene products, including E, Z isomers, might be obtained by dehydration of 3-methyl-3-hexanol with aqueous sulfuric acid?

Question: One problem with elimination reactions is that mixtures of products are often formed. For example, treatment of 2-bromo-2-methylbutane with KOH in ethanol yields a mixture of two alkene products. What are their likely structures?

Question: How many alkene products, including E, Z isomers, might be obtained by dehydration of 3-methyl-3-hexanol with aqueous sulfuric acid?

What product would you expect from the reaction of cyclopentene with NBS and water? Show the stereochemistry.

Question: What product would you expect to obtain from addition of   to 1,2-dimethyl-cyclohexene? Show the stereochemistry of the product.

Question: Addition of HCl to 1,2-dimethylcyclohexene yields a mixture of two products. Show the stereochemistry of each, and explain why a mixture is formed.

When an unsymmetrical alkene such as propene is treated with N-bromosuccinimide in aqueous dimethyl sulfoxide, the major product has the bromine atom bonded to the less highly substituted carbon atom. Is this Markovnikov or non-Markovnikov orientation? Explain

What products would you expect from oxymercuration-demercuration of the following alkenes?

a) 

b)

What products would you expect from oxymercuration-demercuration of the following alkenes?

a) 

b) 

From what alkenes might the following alcohols have been prepared?

a) 

From what alkenes might the following alcohols have been prepared?

b) 

What alkenes might be used to prepare the following alcohols by hydroboration-oxidation?

The following cycloalkene gives a mixture of two alcohols on hydroboration followed by oxidation. Draw the structure of both, and explain the result.

What products would you obtain from catalytic hydrogenation of the following alkenes?

One of the chain-termination steps that sometimes occurs to interrupt polymerization is the following reaction between two radicals. Propose a mechanism for the reaction, using fishhook arrows to indicate electron flow.

What products are formed from hydration of 4-methyl cyclopentane? What can you say about the relative amounts of the products?

Propose a curved-arrow mechanism to show how ozone (O₃) reacts

with a carbon–carbon double bond to form a molozonide, the first intermediate

in ozonolysis.

Which of the reactions below would result in a product mixture that would rotate plane-polarized light?

a) 

Which of the reactions below would result in a product mixture that would rotate plane-polarized light?

b) 

Which of the reactions below would result in a product mixture that would rotate plane-polarized light?

c) 

Iodine azide, adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1-butene is used, only one product results:

a) Add lone-pair electrons to the structure shown for, and draw a

second resonance form for the molecule.

Iodine azide, adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1-butene is used, only one product results:

b) Calculate formal charges for the atoms in both resonance structures you drew for ,in part (a).

Iodine azide, , adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1-butene is used, only one product results:

c) 

In light of the result observed when ,adds to 1-butene, what is

the polarity of the bond? Propose a mechanism for the reaction

using curved arrows to show the electron flow in each step.

10-Bromo-a-chamigrene, a compound isolated from marine algae, is thought to be biosynthesized from g-bisabolene by the following route:

Draw the structures of the intermediate bromonium and cyclic carbocation, and propose mechanisms for all three steps.

Isolated from marine algae, prelaureatin is thought to be biosynthesized from laurediol by the following route. Propose a mechanism

Poly (vinyl pyrrolidone), prepared from N-vinylpyrrolidone, is used in cosmetics and as a synthetic substitute for blood. Draw a representative segment of the polymer.

When a single alkene monomer, such as ethylene, is polymerized, the product is a homopolymer. If a mixture of two alkene monomers is polymerized, however, a copolymer often results. The following structure represents a segment of a copolymer called Saran. What two monomers were copolymerized to make Saran?

Compound A has the formula ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{16}}$. On catalytic hydrogenation over palladium, it reacts with only 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$. Compound A also undergoes reaction with ozone, followed by zinc treatment, to yield a symmetrical diketone, $\mathbf{B}\left(C_{10}{H}_{16}{O}_2\right)$.

How many rings does A have?

Compound A has the formula ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{16}}$. On catalytic hydrogenation over palladium, it reacts with only 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$. Compound A also undergoes a reaction with ozone, followed by zinc treatment, to yield a symmetrical diketone, B$\left(C_{10}{H}_{16}{O}_2\right)$. 

What are the structures of A and B?

Compound A has the formula ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{16}}$. On catalytic hydrogenation over palladium, it reacts with only 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$. Compound A also reacts with ozone, followed by zinc treatment, to yield a symmetrical diketone, B$\left(C_{10}{H}_{16}{O}_2\right)$.

Write the reactions.

An unknown hydrocarbon A with the formula ${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{12}}$ reacts with 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$ over a palladium catalyst. Hydrocarbon A also reacts with ${\mathbf{OsO}}_{\mathbf{4}}$ to give diol B. When oxidized with ${\mathbf{KMnO}}_{\mathbf{4}}$ in acidic solution, A gives two fragments. One fragment is propanoic acid, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}\mathbf{H}$, and the other fragment is ketone C. What are the structures of A, B, and C? Write all reactions, and show your reasoning.

Using an oxidative cleavage reaction, explain how you would distinguish between the following two isomeric dienes:

Compound A, C₁₀H₁₈O, undergoes reaction with dilute H₂SO₄ at 50 °C to yield a mixture of two alkenes, C₁₀H₁₆. The major alkene product, B, gives only cyclopentanone after ozone treatment followed by reduction with zinc in acetic acid. Identify A and B, and write the reactions. 

Cyclopentanone

Draw the structure of a hydrocarbon that absorbs 2 molar equivalents of H2 on catalytic hydrogenation and gives only butanedial on ozonolysis.

Butanedial

Simmons–Smith reaction of cyclohexene with diiodomethane gives a single cyclopropane product, but the analogous reaction of cyclohexene with 1,1-diiodoethane gives (in low yield) a mixture of two isomeric methylcyclopropane products. What are the two products, and how do they differ?

Compound A has the formula ${\mathit{C}}_{\mathbf{8}}{\mathit{H}}_{\mathbf{8}}$. It reacts rapidly with $\mathit{K}\mathit{M}\mathit{n}{\mathit{O}}_{\mathbf{4}}$to give $\mathit{C}{\mathit{O}}_{\mathbf{2}}$ and a carboxylic acid, B $\left({\mathit{C}}_7{\mathit{H}}_6{\mathit{O}}_2\right)$, but reacts with only 1 molar equivalent of ${\mathbf{H}}_{\mathbf{2}}$on catalytic hydrogenation over a palladium catalyst. On hydrogenation under conditions that reduce aromatic rings, 4 equivalents of ${\mathbf{H}}_{\mathbf{2}}$ are taken up and hydrocarbon C $\left({\mathit{C}}_8{\mathit{H}}_{16}\right)$is produced. What are the structures of A, B, and C? Write the reactions.

The following alkene undergoes hydroboration–oxidation to yield a single product rather than a mixture. Explain the result, and draw the product showing its stereochemistry.

Evidence that cleavage of 1,2-diols by ${\mathbf{HIO}}_{\mathbf{4}}$occurs through a five membered cyclic periodate intermediate is based on kinetic data—the measurement of reaction rates. When diols A and B were prepared and the rates of their reaction with ${\mathbf{HIO}}_{\mathbf{4}}$were measured, it was found that diol A cleaved approximately 1 million times faster than diol B. Make molecular models of A and B and of potential cyclic periodate intermediates, and then explain the kinetic results

$\mathbf{\alpha }$-Terpinene, ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{16}}$is a pleasant-smelling hydrocarbon that has been isolated from oil of marjoram. On hydrogenation over a palladium catalyst, $\mathbf{\alpha }\mathbf{-}$terpinene reacts with two molar equivalents ${\mathbf{H}}_{\mathbf{2}}$to yield a hydrocarbon, ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{20}}$.On ozonolysis, followed by reduction with zinc and acetic acid, $\mathbf{\alpha }\mathbf{-}$terpinene delivers two products, glyoxal, and 6-methyl-2,5- heptane dione.

(a) How many degrees of unsaturation does $\mathbf{\alpha }\mathbf{-}$terpinene have? 

(b) How many double bonds and how many rings does it have? 

(c) Propose a structure for $\mathbf{\alpha }\mathbf{-}$terpinene

How would you distinguish between the following pairs of compounds using simple chemical tests? Tell what you would do and what you would see. 

(a) Cyclopentene and cyclopentane

Compound A, ${\mathbf{C}}_{\mathbf{11}}{\mathbf{H}}_{\mathbf{16}}\mathbf{O}$, was found to be an optically active alcohol. Despite its apparent unsaturation, no hydrogen was absorbed on catalytic reduction over a palladium catalyst. On treatment of A with dilute sulfuric acid, dehydration occurred and an optically inactive alkene B, ${\mathbf{C}}_{\mathbf{11}}{\mathbf{H}}_{\mathbf{14}}$, was the major product. Alkene B, on ozonolysis, gave two products. One product was identified as propanal, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CHO}$. Compound C, the other product, was shown to be a ketone, ${\mathbf{C}}_{\mathbf{8}}{\mathbf{H}}_{\mathbf{8}}\mathbf{O}$. How many degrees of unsaturation does A have? Write the reactions, and identify A, B, and C.

Hydroxylation of cis-2-butene with ${\mathbf{OsO}}_{\mathbf{4}}$yields a different product than hydroxylation of trans-2-butene. Draw the structure, show the stereochemistry of each product, and explain the difference between them.

Reaction of HBr with 3-methylcyclohexene yields a mixture of four products: cis- and trans-1-bromo-3-methylcyclohexane and cis- and trans-1-bromo-2-methylcyclohexane. The analogous reaction of HBr with 3-bromocyclohexene yields trans-1,2-dibromocyclohexane as the sole product. Draw structures of the possible intermediates, and then explain why only a single product is formed in this reaction.

How would you distinguish between the following pairs of compounds using simple chemical tests? Tell what you would do and what you would see. 

(b) 2-Hexene and benzene

Reaction of 2-methylpropene with CH₃OH in the presence of H₂SO₄

catalyst yields methyl tert-butyl ether, CH₃OC(CH₃)₃, by a mechanism

analogous to that of acid-catalyzed alkene hydration. Write the mechanism,

using curved arrows for each step.