Ch. 6: The Reactions of Alkenes / The Stereochemistry of Addition Reactions

Question 1

What are electrophilic addition reactions?

Answer 1

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.

Question 2

A curved arrow always points from the

(1) __________ to the (2) ___________ .

Answer 2

(1) electron donor

(2) electron acceptor

Question 3

The addition of hydrogen halides and the acid-catalyzed addition of water and alcohols form _____________ .

Answer 3

carbocation intermediates

Question 4

List the 3 different carbocations from most stable to least stable.
Is a less stable or more stable carbocation formed more rapidly?

Answer 4

Tertiary carbocations are more stable than secondary carbocations, which are more stable than primary carbocations.
A more stable carbocation is formed more rapidly.

Question 5

What is the Hammond postulate?

Answer 5

The Hammond postulate states that a transition state is more similar in structure to the species to which it is closer in energy.

Question 6

Define regioselectivity.

Answer 6

Regioselectivity is the preferential formation of one constitutional isomer over another.

Question 7

A carbocation will _________ if it becomes more stable as a result of the rearrangement.

Answer 7

rearrange

Question 8

What kinds of shifts cause carbocation rearrangements?

Answer 8

1,2-hydride shifts and 1,2-methyl shifts cause carbocation rearrangements.

Question 9

If a reaction does not form a ___________, a carbocation rearrangement cannot occur.

Answer 9

carbocation intermediate

Question 10

The addition of ____________ forms an intermediate with a 3-membered ring that reacts with nucleophiles.

Answer 10

Br2 or Cl2

Question 11

____________ forms an intermediate with a 5-membered ring.

Answer 11

Ozonolysis

Question 12

What kinds of reactions do not form an intermediate?

Answer 12

Hydroboration, epoxidation, and catalytic hydrogenation do not form an intermediate.

Question 13

Oxidation reaction vs. reduction reaction

Answer 13

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.

Question 14

How do you determine the product of oxidative cleavage?

Answer 14

To determine the product of oxidative cleavage, you replace the C = C with
C = O O = C.

Question 15

Ketone vs. aldehyde

Answer 15

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).

Question 16

______________ reduces alkenes to alkanes.

Answer 16

Catalytic hydrogenation

Question 17

(1) ______________ is the heat released in a hydrogenation reaction. It is the delta H value without (2) _________ .

Answer 17

(1) The heat of hydrogenation

(2) negative sign

Question 18

The ___________ has the smallest heat of hydrogenation.

Answer 18

most stable alkene

Question 19

The stability of an alkene increases as the number of ____________ bonded to its sp2 carbons increases.

Answer 19

alkyl groups

Question 20

Are trans alkenes or cis alkenes more stable? Why?

Answer 20

Trans alkenes are more stable than cis alkenes due to less steric strain.

Question 21

Regioselective vs. stereoselective vs. enantioselective

Answer 21

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.

Question 22

What does stereospecific mean?

Answer 22

A reaction is stereospecific if the reactant can exist as stereoisomers and each stereoisomer forms a different stereoisomer or a different set of stereoisomers.

Question 23

When a reactant that does not have an asymmetric center forms a product with one asymmetric center, the product will be a ________________ .

Answer 23

racemic mixture

Question 24

When a reactant that has an asymmetric center forms a product with a second asymmetric center, the product will be ___________________________.

Answer 24

diastereomers in unequal amounts

Question 25

Syn addition vs. anti addition

Answer 25

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.

Question 26

What do syn addition and anti addition have in common?

Answer 26

Both syn and anti additions occur in electrophilic addition reactions that form a carbocation intermediate.

Question 27

The addition of (1) ____________ to an alkene is a syn addition reaction;
(2) ________________ is overall a syn addition of water.

Answer 27

(1) H2 or peroxyacid

(2) hydroboration-oxidation

Question 28

The addition of _____________ is an anti addition reaction.

Answer 28

Br2 or Cl2

Question 29

An (1) ____________ forms only one stereoisomer, and an enzyme typically catalyzes the reaction of (2) __________ stereoisomer.

Answer 29

(1) enzyme-catalyzed reaction

(2) only one

Question 30

An ____________ reacts identically with both geometric isomers or with enantiomers.

Answer 30

achiral reagent

Question 31

A _____________ reacts differently with each geometric isomer or with each enantiomer.

Answer 31

chiral reagent