Chapter 6.3: Electrophile Additions Flashcards
What is the gain of electrons. Alternatively, either the gain of hydrogen, loss of oxygen, or both?
reduction
What is a reaction in which one stereoisomer is formed in preference to all others?
stereoselective reaction
What is the stereochemistry of Acid-catalyzed hydration?
Mixed
What is the stereochemistry of the addition of bromine or chlorine to an alkene?
anti addition –> trans products
What is a type of rearrangement in which an atom or group of atoms with its bonding electrons moves from one atom to an adjacent electron-deficient atom?
1,2 shift
Define inductive effect
the polarization of the electron density of a covalent bond caused by the electronegativity of a nearby atom
Describe the mechanism behind the addition of water to an alkene (Acid-Catalyzed Hydration)
o In the presence of an acid catalyst, most commonly concentrated sulfuric acid, water adds to an alkene to give an alcohol
o Step 1: Add a proton
o Step 2: Make a new bond between a nucleophile and an electrophile
o Step 3: Take a proton away
o In the case of simple alkenes, H adds to the carbon of the double bond with the greater number of hydrogens and OH adds to the carbon with the fewer hydrogens
Define hydration
the addition of water
What is the regiochemistry of the addition of a hydrogen halide to an alkene?
Markovinikov
Define regioselective reaction
an addition or substitution reaction in which one of two or more possible products is formed in preference to all others that might be formed
Describe the mechanism of oymercuration-reduction of an alkene
o The hydration of an alkene can be accomplished by treating it with mercury (II) acetate (mercuric acetate) in water followed by reduction of the resulting organomercury compound with sodium borohydride, NaBH4
o Step 1: Break a bond to give stable molecules of ions
o Step 2: Make a new bond between a nucleophile (pi bond) and an electrophile
o Step 3: Make a new bond between a nucleophile and an electrophile
o Step 4: Take a proton away
o Step 5: Reduction of the C-HgOAc bond to a C-H bond gives the final product and metallic mercury
Define 1,2 shift
a type of rearrangement in which an atom or group of atoms with its bonding electrons moves from one atom to an adjacent electron-deficient atom
What is the addition of water?
hydration
What is an addition or substitution reaction in which one of two or more possible products is formed in preference to all others that might be formed?
regioselective reaction
Define antistereoselectivity
the addition of atoms or groups of atoms to opposite faces of a carbon-carbon double bond
What is the stereochemistry of the addition of a hydrogen halide to an alkene?
mixed
What is the regiochemistry of the addition of HOCl and HOBr to an alkene?
OH ends up on more substituted C atom
What is - a compound containing a halogen atom and a hydroxyl group on adjacent atoms; those containing Br and OH are bromohydrins, and those containing Cl and OH are chlorohydrins?
halohydrins
Define stereoselective reaction
a reaction in which one stereoisomer is formed in preference to all others. A stereoselective reaction may be enantioselective or diastereoselective
Describe the mechanism behind the addition of a hygrogen halide to an alkene
o Summary: The hydrogen halides HCl, HBr, and HI add to alkenes to give a carbocation intermediate that reacts with X- to give haloalkenes
o Step 1: Addition of a proton to the alkene, results in formation of a cationic intermediate
o Step 2: Make a new bond between a nucleophile and an electrophile
Define reduction
the gain of electrons. Alternatively, either the gain of hydrogen, loss of oxygen, or both
Define Markovnikov’s rule
in the addition of HX, H2O, or ROH to an alkene, hydrogen adds to the carbon of the double bond having the greater number of hydrogens
Define hyperconjugation
interaction of electrons in a σ-bonding orbital with the vacant 2p orbital of an adjacent positively charged carbon
Define oxymercuration
a method for converting an alkene to an alcohol. The alkene is treated with mercury (II) acetate followed by reduction with sodium borohydride
Define electrophilic addition
a common type of reaction with alkenes in which an electrophile species adds to pi bond
What is the regiochemistry of Acid-catalyzed hydration?
Markovnikov’s Rule
What typically happens in carbocation rearrangements?
Typically, either an alkyl group or a hydrogen migrates, each with its bonding electrons, from an adjacent atom to the electron-deficient atom
What is a method for converting an alkene to an alcohol. The alkene is treated with mercury (II) acetate followed by reduction with sodium borohydride?
oxymercuration
What is the interaction of electrons in a σ-bonding orbital with the vacant 2p orbital of an adjacent positively charged carbon?
hyperconjugation
What is a species in which a carbon atom has only six electrons in its valence shell and bears a positive charge?
carbocation
What is a common type of reaction with alkenes in which an electrophile species adds to pi bond?
electrophilic addition
Define rearrangement
a change in connectivity of the atoms in a product compared with the connectivity of the same atoms in the starting material
What is the polarization of the electron density of a covalent bond caused by the electronegativity of a nearby atom?
inductive effect
What is a change in connectivity of the atoms in a product compared with the connectivity of the same atoms in the starting material?
rearrangement
What are the 3 characteristics of electrophile species?
o Low electron density, reflected by a partial or full positive charge
o Lack of an octet on an atom
o Relatively weak bond to an atom that can depart as stable ion or molecule
Describe the mechanism behind the addition of HOCl and HOBR to an alkene
o Treating an alkene with Br2 or Cl2 in the presence of water results in addition of OH and Br, or OH and Cl, to the carbon-carbon double bond
o Step 1: Make a new bond between a nucleophile (pi bond) and an electrophile
o Step 2: Make a new bond between a nucleophile and an electrophile
o Step 3: Take a proton away
Define halohydrin
- a compound containing a halogen atom and a hydroxyl group on adjacent atoms; those containing Br and OH are bromohydrins, and those containing Cl and OH are chlorohydrins
What is the stereochemistry of the addition of HOCl and HOBr to an alkene?
anti –> “H2O attacks from the back”
Define carbocation
a species in which a carbon atom has only six electrons in its valence shell and bears a positive charge
Describe the mechanism behind the addition of bromine or chlorine to an alkene
o Cl2 and Br2 react with alkenes at room temperature by adding halogen atoms to the two carbon atoms of the double bond with formation of two new carbon-halogen bonds
o Step 1: Make a new bond between a nucleophile (pi bond) and an electrophile
o Step 2: Make a new bond between a nucleophile and an electrophile
What is in the addition of HX, H2O, or ROH to an alkene, hydrogen adds to the carbon of the double bond having the greater number of hydrogens?
Markovnikov’s rule
