chapter 6

Question 0

hydrogenation

Answer 0

the addition of H2 to a multiple bond

Question 1

unsaturated hydrocarbons

Answer 1

alkenes that have the capacity to react with substances that add to them

Question 2

heat of hydrogenation

Answer 2

hydrogenation of all alkenes is exothermic

Question 3

platinum

Answer 3

hydrogenation catalyst most often used

-palladium, nickel, and rhodium are also used

Question 4

metal-catalyzed addition of H2

Answer 4

is normally rapid at room temp and alkane yield is very high (usually only product)

Question 5

heterogeneous reactions

Answer 5

reactions involving a substance in one phase with a different substance in a second phase

Question 6

decreasing heat of hydrogenation

increasing stability of the double bond

Answer 6

ethylene>monosubstituted>disubstituted>tri>tetra

H2C=CH2>RCH=CH2>RCH=CHR>R2C=CHR>R2C=CR2

Question 7

Mechanism
Hydrogenation of alkenes
Step 1

Answer 7

1. H molecules react w/metal atoms at the catalyst surface. The relatively strong H-H sigma bond is broken and replaced by 2 weak metal-H bonds.

Question 8

Mechanism
hydrogenation of alkenes
Step 2

Answer 8

2. Alkene reacts w/metal catalyst. The pi component of the = bond between 2 C’s is replaced by 2 relatively weak C-metal sigma bond

Question 9

Mechanism
hydrogenation of alkenes
Step 3

Answer 9

3. H atom is transferred from the catalyst surface to 1 of the C’s of the = bond

Question 10

Mechanism
hydrogenation of alkenes
step 4

Answer 10

4. Second H atom is transferred, forming the alkane. Sites on catalyst surface at which the reaction occurred are free to acept additional H’s and alkene molecules

Question 11

stereochemistry

syn addition

Answer 11

H atoms are added to the same face of the double bond (same side)
-start with a molecule and add H2, the result is a product with H’s that are cis

Question 12

stereoselectivity

Answer 12

stereoselective reaction starts with a single reactant and give two or more stereoisometric products but yields one of them in greater amounts

Question 13

Electrophilic addition of Hydrogen halides to alkenes

Answer 13

• addition of polar molecule (H2 is nonpolar)
• addition happens rapidly
• two step mechanism

Question 14

Mechanism

electrophilic addition of a hydrogen halide to an alkene

Answer 14

1. hydrogen halide donates proton to alkene, forming a carbocation (slow)
2. carbocation-anion combination (fast)

Question 15

increasing reactivity of hydrogen halides in addition to alkenes

Answer 15

HF«HI

Question 16

Protonation of the C-C double bond

Answer 16

• pi electrons are in the double bond

- are only interested in something with a + charge, especially H+

Question 17

electrophilic

Answer 17

positively polarized

-H+

Question 18

Markovnikov’s rule

Answer 18

when an unsymmetrically substituted alkene reacts with a hydrogen halide, the H adds to the C that has the greater numbers of H’s, and the halogen adds to the C having fewer H’s

Question 19

alkyl groups

Answer 19

• are electron-releasing

- the more electron rich a double bond, the better it can share its pi electrons with an electophile

Question 20

hydroboration/oxidation reactions

Answer 20

• results in primary alcohol
• does not form carbocations
• syn addition (H and OH are cis)
• makes one product exclusively
• regioselectivity and stereochemistry control

Question 21

hydration of alkenes

Answer 21

by using sulfuric acid and then H2O is the reversible dehydration of alcohol reaction
-it is limited to mono and di substituted alkenes

Question 22

relative rates of acid-catalyzed hydration of alkenes

Answer 22

ethylene (H2C=CH2)<2-Methylpropene ((CH3)2C=CH2)

Question 23

hydroboration-oxidation of alkenes

Answer 23

• carry out step 1 (hydroboration) by adding Boron
• then carry out step 2 (oxidation) by adding a base (H2O2, NaOH, H2O)
• reaction must be carried out in dry conditions (no H2O)

Question 24

hydroboration

Answer 24

a reaction in which a boron hydride adds to a C-C pi bond

-a C-H and C-B bond result

Question 25

oxidation stage

Answer 25

the organic borane is oxidized by hydrogen peroxide (H2O2

Question 26

addition of halogens to alkenes

Answer 26

halogens normally react with alkenes by electrophilic addition

ex. C=C + Br2 –> Br-C-C-Br
- alkenes can remove color from Br2 making it a colorless product
- uses either bromine (Br2) or chlorine (Cl2)

Question 27

vicinal dihalides

Answer 27

products of addition of halogens to alkene reaction

Question 28

anti addition

Answer 28

is observed in halogen addition to cycloalkenes

Question 29

vicinal halohydrins

Answer 29

compounds that have a halogen and a hydroxyl group on adjacent carbons

ex. C=C + Cl2 + H20 –> HO-C-C-Cl +HCl
- anti addition occurs (the halogen and hydroxyl group add to opposite faces)

Question 30

free radical addition of hydrogen bromide to alkenes

Answer 30

• Br is electophile in the presence of peroxides
  
  • H+ is electrophile without peroxides
• Br being electrophile causes the reversal reaction of Markovnik’s rule

Question 31

No peroxides

Answer 31

Markovnik’s rule

Question 32

peroxides

Answer 32

reversal of Markonvik’s rule

Question 33

epoxides

Answer 33

are rings with Oxygen in them

• alkenes react with peroxides to make epoxides
• electrophilic addition reaction

Question 34

ozonolysis

Answer 34

two-stage reaction sequence that requires two different recipes
1. O3; H2O; Zn
or
2. O3; CH3OH; (CH3)2S

Question 35

ozonolysis

Answer 35

• breaks C=C and makes two C=O

- used to piece together the original reactants by looking at products formed