Ch. 6: The Reactions of Alkenes / The Stereochemistry of Addition Reactions Flashcards
What are electrophilic addition reactions?
These reactions start with the addition of an electrophile to the sp2 carbon bonded to the most hydrogens and end with the addition of a nucleophile to the other sp2 carbon.
A curved arrow always points from the
(1) __________ to the (2) ___________ .
(1) electron donor
(2) electron acceptor
The addition of hydrogen halides and the acid-catalyzed addition of water and alcohols form _____________ .
carbocation intermediates
List the 3 different carbocations from most stable to least stable.
Is a less stable or more stable carbocation formed more rapidly?
Tertiary carbocations are more stable than secondary carbocations, which are more stable than primary carbocations.
A more stable carbocation is formed more rapidly.
What is the Hammond postulate?
The Hammond postulate states that a transition state is more similar in structure to the species to which it is closer in energy.
Define regioselectivity.
Regioselectivity is the preferential formation of one constitutional isomer over another.
A carbocation will _________ if it becomes more stable as a result of the rearrangement.
rearrange
What kinds of shifts cause carbocation rearrangements?
1,2-hydride shifts and 1,2-methyl shifts cause carbocation rearrangements.
If a reaction does not form a ___________, a carbocation rearrangement cannot occur.
carbocation intermediate
The addition of ____________ forms an intermediate with a 3-membered ring that reacts with nucleophiles.
Br2 or Cl2
____________ forms an intermediate with a 5-membered ring.
Ozonolysis
What kinds of reactions do not form an intermediate?
Hydroboration, epoxidation, and catalytic hydrogenation do not form an intermediate.
Oxidation reaction vs. reduction reaction
Oxidation reaction decreases the # of C-H bonds and/or increases the # of C-N, C-O, and C-X (where X is a halogen) bonds.
Reduction reaction decreases the # of C-N, C-O, and C-X bonds and/or increases the # of C-H bonds.
How do you determine the product of oxidative cleavage?
To determine the product of oxidative cleavage, you replace the C = C with
C = O O = C.
Ketone vs. aldehyde
A ketone has 2 alkyl groups bonded to a carbonyl C = O group (generally R2C=O).
An aldehyde has one hydrogen (or has 2 hydrogens) bonded to a carbonyl group (generally RHC=O).
______________ reduces alkenes to alkanes.
Catalytic hydrogenation
(1) ______________ is the heat released in a hydrogenation reaction. It is the delta H value without (2) _________ .
(1) The heat of hydrogenation
(2) negative sign
The ___________ has the smallest heat of hydrogenation.
most stable alkene
The stability of an alkene increases as the number of ____________ bonded to its sp2 carbons increases.
alkyl groups
Are trans alkenes or cis alkenes more stable? Why?
Trans alkenes are more stable than cis alkenes due to less steric strain.
Regioselective vs. stereoselective vs. enantioselective
A regioselective reaction selects for a particular constitutional isomer.
A stereoselective reaction selects for a particular stereoisomer.
An enantioselective reaction selects for a particular enantiomer.
What does stereospecific mean?
A reaction is stereospecific if the reactant can exist as stereoisomers and each stereoisomer forms a different stereoisomer or a different set of stereoisomers.
When a reactant that does not have an asymmetric center forms a product with one asymmetric center, the product will be a ________________ .
racemic mixture
When a reactant that has an asymmetric center forms a product with a second asymmetric center, the product will be ___________________________.
diastereomers in unequal amounts
Syn addition vs. anti addition
In syn addition, the substituents add to the same side of a double bond.
In anti addition, the substituents add to opposite sides of a double bond.
What do syn addition and anti addition have in common?
Both syn and anti additions occur in electrophilic addition reactions that form a carbocation intermediate.
The addition of (1) ____________ to an alkene is a syn addition reaction;
(2) ________________ is overall a syn addition of water.
(1) H2 or peroxyacid
(2) hydroboration-oxidation
The addition of _____________ is an anti addition reaction.
Br2 or Cl2
An (1) ____________ forms only one stereoisomer, and an enzyme typically catalyzes the reaction of (2) __________ stereoisomer.
(1) enzyme-catalyzed reaction
(2) only one
An ____________ reacts identically with both geometric isomers or with enantiomers.
achiral reagent
A _____________ reacts differently with each geometric isomer or with each enantiomer.
chiral reagent
