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Chapter 12
Reactions of Alkenes
54
Organic Chemistry
Undergraduate 2
11/16/2014

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Term
Thermodynamically, additions to alkenes should proceed to products with _____ of energy
Definition
release
Term
syn addition
Definition
adding reagents to the same side of the double bond in an alkene
Term
anti addition
Definition
adding reagents to opposite sides of the double bond in an alkene
Term
When steric hindrance inhibits hydrogenation on one face of a double bond, addition will take place exclusively to the _____ face
Definition
less hindered
Term
An electrophilic oxidizing agent is capable of introducing a single _____ atom to connect both carbons of a double bond
Definition
oxygen
Term
The process of introducing a single oxygen atom to connect both carbons of a double bond produces oxacyclopropanes, which may be converted into vicinal _____ diols
Definition
anti
Term
The attachment of oxygen atoms to _____ alkene carbon gives vicinal syn diols by partial double-bond cleavage
Definition
each
Term
The attachment of oxygen atoms to each alkene carbon gives vicinal _____ diols by partial double-bond cleavage
Definition
syn
Term
The OH group in peroxycarboxylic acids contains an _____ oxygen
Definition
electrophilic
Term
epoxidation
Definition
the transformation of an alkene to an oxacyclopropane
Term
"Epoxidation" is derived from "_____", one of the older common names for oxacyclopropanes
Definition
epoxide
Term
Are additions in peroxide conditions faster or slower than ionic additions?
Definition
much faster
Term
radical chain sequence
Definition
additions of radicals to an alkene in the presence of peroxides
Term
What are the 2 initiation steps for the anti-Markovnikov hydrobromination in the presence of radicals?
Definition
1. the hemolytic cleavage of the weak RO-OR bond
2. reaction of the resulting alkoxy radical with hydrogen bromide
Term
In anti-Markovnikov addition, the halogen atom's attack is _____, creating the relatively more stable secondary radical rather than the primary one
Definition
regioselective
Term
In the radical mechanism, a _____ atom is the attacking species, creating the more stable radical center
Definition
bromine
Term
In the _____ mechanism, a halogen atom is the attacking species, creating the more stable radical center
Definition
radical
Term
Which 2 H-X molecules do not give anti-Markovnikov addition products with alkenes?
Definition
hydrogen chloride & hydrogen iodide
Term
Can HCl & HI give anti-Markovnikov addition products with alkenes?
Definition
no!
Term
What is the only H-X molecule that adds to an alkene under radical conditions to give anti-Markovnikov products?
Definition
HBr
Term
In bromination, only _____ addition is observed
Definition
anti
Term
When the pi electron could of the alkene attacks one end of the Br2 molecule, what is formed?
Definition
a cyclic bromonium ion
Term
The halogenation of alkenes should not be confused with the halogenation of _____
Definition
alkanes
Term
_____ halogenation is a radical process that requires an initiation step to generate halogen atoms
Definition
alkane
Term
The nucleophile attacks the _____ carbon of the ring, because this carbon is more positively polarized than the other
Definition
more highly substituted
Term
ozonolysis
Definition
oxidatively cleaving alkenes (pi and sigma bonds) through the reaction with ozone (O3)
Term
Ozone is produced in the laboratory in an instrument called an _____, in which an arc discharge generates 3-4% ozone in a dry oxygen stream
Definition
ozonator
Term
ozonide
Definition
the first isolable intermediate in ozonolysis; reduced directly in a subsequent step by exposure to zinc in acetic acid or by reaction with dimethyl sulfide
Term
molozonide
Definition
the product of the initial electrophilic addition of ozone to the double bond of an alkene
Term
2 step mechanism of ozonolysis
Definition
1. molozonide formation & cleavage
2. ozonide formation & reduction
Term
Transformations that end in hydrogenation are collectively called _____
Definition
electrophilic additions
Term
electrophilic addition
Definition
when a good nucleophile is present & a carbocation is intercepted after hydrogenation
Term
In electrophilic addition, when the two vinyl carbons have the same substituents, protonation to either carbon furnishes the _____ intermediate cation
Definition
same
Term
If the carbon atoms participating in the double bond are not equally substituted, the proton from the hydrogen halide attaches itself to which carbon?
Definition
the less substituted carbon
Term
Markovnikov rule
Definition
protonation of an alkene results in the hydrogen bonding to the less substituted carbon
Term
Why is Markovnikov rule true?
Definition
the relative stability of the resulting carbocation intermediate
Term
Which carbocations are the most stable?
Definition
tertiary > secondary > primary
Term
H-X adds to unsymmetric alkenes in such a way that the initial protonation gives ______
Definition
the more stable carbocation
Term
Upon exposure of an alkene to an _____ solution of sulfuric acid, water acts as the nucleophile to trap the carbocation formed by initial protonation
Definition
aqueous
Term
electrophilic hydration
Definition
when the elements of water add to the double bond
Term
Are the steps reversible in the mechanism of alkene hydration?
Definition
yes!
Term
Treating the alcohol with _____ favors dehydration into the alkene, especially at elevated temperatures
Definition
concentrated acid
Term
Is the E1 process that forms alkenes reversible?
Definition
yes!
Term
The INITIAL E1 formation of alkenes is under _____ control
Definition
kinetic
Term
The net effect of E1 formation of alkenes is interconversion of the isomers to an equilibrium mixture, in which the _____ most stable isomer is the major component
Definition
thermodynamically
Term
The E1 formation of alkenes is overall under _____ control
Definition
thermodynamic
Term
mercuration
Definition
an electrophilic addition of a mercuric salt to an alkene; resulting compound is an alkyl-mercury derivative, from which the mercury can be removed in a subsequent step
Term
oxymercuration-demercuration
Definition
a mercuric acetate acts as the reagent; treatment of an alkene with this species in the presence of water leads to the corresponding addition product; then, the mercury-containing substituent is replaced by hydrogen through treatment with sodium borohydride in base; net result is hydration of the double bond to give an alcohol
Term
What is the significance behind no carbocation being involved in oxymercuration-demercuration?
Definition
oxymercuration-demercuration is not susceptible to the rearrangements that commonly occur under acidic condition
Term
4 step mechanism of oxymercuration-demercuration
Definition
1. dissociation
2. electrophilic attack
3. nucleophilic opening
4. reduction
Term
hydroboration
Definition
borane adding to double bonds without catalytic activation; discovered by H.C. Brown
Term
hydroboration-oxidation
Definition
the addition of the elements of water to a double bond with opposite regioselectivity from Markovnikov (the OH group ends up at the less substituted carbon)
Term
In hydroboration-oxidation, the OH group ends up at the _____ substituted carbon, an example of anti-Markovnikov addition
Definition
less
Term
In hydroboration, the addition occurs without the participation of carbocations; therefore, _____ are not observed
Definition
rearrangements
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