FINALS 9

Question 1

Alkenes behave as ____________ in polar reactions, donating a pair of electrons from their electron-rich C=C bond to an electrophile (Lewis acid).

Answer 1

nucleophiles (Lewis bases)

Question 2

Carbon–carbon ___ bond is replaced by two ___ bonds.

Answer 2

π

σ

Question 3

◦ high electron density above and below the plane of molecule
◦ more polarizable than σ bond
◦ can interact with a positively charged electrophile

Answer 3

alkene π bond

Question 4

Alkene forms a ___________ when π electrons form a σ bond with an E+ and leave the other carbon electron-deficient.

Answer 4

carbocation intermediate

Question 5

Electrons from a Nu- are donated to the carbocation forming a second σ bond

Question 6

rate-limiting step:

Answer 6

carbocation formation

Question 7

yields alkyl halides, RX

Answer 7

hydrohalogenation reactions

Question 8

proposed in 1869 by Russian chemist Vladimir Markovnikov

addition of HX across a carbon–carbon multiple bond proceeds in such a way that
the proton adds to the less-substituted carbon atom

the more highly substituted carbocation is formed as the intermediate rather than the less highly substituted one the electrophile adds to the double bond to form the more stable carbocation

Answer 8

MARKOVNIKOV’S RULE

Question 9

more alkyl groups on carbocation → more possibilities for _________ → more stable carbocation

Answer 9

hyperconjugation

Question 10

• yields alcohols, ROH
• requires acid catalyst
• also follows Markovnikov’s rule

Answer 10

hydration reactions

Question 11

◦ suited to large-scale industrial procedures (e.g., ethanol production from ethylene)
◦ of little value in the typical laboratory because it requires high temperatures and strongly
acidic conditions

Answer 11

acid-catalyzed alkene hydration

Question 12

◦ electrophilic addition of Hg2+ to alkene on reaction with mercury(II) acetate (CH3CO2)2Hg/
Hg(OAc)2 in aqueous tetrahydrofuran (THF) solvent
◦ formation of mercurinium ion intermediate
◦ nucleophilic addition of water followed by loss of proton
◦ forms a stable intermediate organomercury compound

Answer 12

Oxymercuration

Question 13

◦ treatment of intermediate organomercury compound with sodium borohydride
◦ produces alcohol

Answer 13

demercuration

Question 14

addition of a B-H bond of borane, BH3 (a Lewis acid), to an alkene to yield an

Answer 14

organoborane intermediate, RBH2

Question 15

oxidation of organoborane by reaction with __________, H2O2 to yield an alcohol

Answer 15

basic hydrogen peroxide

Question 16

◦ C-H and C-B bonds form at the same time and from the same face of the alkene
◦ attachment of boron is favored at the less sterically crowded carbon atom

Answer 16

yields a syn non-Markovnikov product

no carbocation intermediate

Question 17

yield alkyl 1,2-dihalides

Answer 17

halogenation reactions (addition of Br2 or Cl2)

Question 18

• no carbocation intermediate
• forms cyclic halonium intermediate (bromonium or chloronium)

Answer 18

ADDITION OF X2 TO ALKENES: MECHANISM

Question 19

◦ the bridging halogen blocks nucleophilic attack on the halogen bonded face of the original double bond
◦ rear side attack opens the cyclic halonium ion

Answer 19

anti stereochemistry

Question 20

symmetrical bromonium ions → identical

Answer 20

yields two enantiomers

Question 21

asymmetrical bromonium molecules → nonidentical

Answer 21

yields one meso compound

Question 22

Disadvantage: not all alkenes take up bromine e.g., those with electron withdrawing
groups → perform ________

Answer 22

Baeyer’s test

Question 23

◦ forms halohydrins (halo-alcohols)

Answer 23

Addition of HOX (HOCl or HOBr)

Question 24

• increases electron density on carbon by:
  forming this: C-H
  or breaking one of these: C-O, C-N, C-X

Answer 24

reduction

Question 25

• decreases electron density on carbon by:
  forming one of these: C-O, C-N, C-X
  or breaking these: C-H

Answer 25

oxidation

Question 26

REDUCTION OF ALKENES:
CATALYTICHYDROGENATION

Alkenes are reduced to ________

Answer 26

alkanes

Question 27

normally used as PtO2 (Adam’s Catalyst)

Answer 27

platinum

Question 28

normally used as very fine powder “supported” on an inert material such as
charcoal (Pd/C)

Answer 28

palladium

Question 29

does not occur in a homogeneous solution but instead takes place on the surface of solid catalyst particles

Answer 29

heterogeneous process

Question 30

both H atoms add on the same more accessible face (less steric hindrance)

Answer 30

syn stereochemistry

Question 31

much more reactive toward catalytic hydrogenation than most other unsaturated functional groups, and the reaction is therefore quite selective.

Answer 31

alkenes

Question 32

Aldehydes, ketones, esters, and nitriles only undergo _________ under more vigorous condition

Answer 32

alkene hydrogenation

Question 33

reduced on a large scale to produce saturated fats used in margarine and cooking products

Answer 33

unsaturated vegetable oils

Question 34

triesters of glycerol with three long-chain carboxylic acids (fatty acids) that are generally polyunsaturated with cis stereochemistry.

Answer 34

vegetable oils

Question 35

yields saturated fatty acids

Answer 35

complete hydrogenation

Question 36

yields trans fatty acids (due to partial cis–trans isomerization of a remaining double bonds) → raises blood cholesterol and contributes to coronary problem

Answer 36

incomplete hydrogenation

Question 37

OXIDATION OF ALKENES: HYDROXYLATION

oxidized to 1,2-diols

Answer 37

Alkenes

Question 38

◦ a large molecule built up by repetitive units smaller molecules called monomers
◦ e.g., cellulose from sugar monomers, proteins from amino acid monomers, and nucleic acids from nucleotide monomers

Answer 38

Polymer

Question 39

a synthetic alkene polymer

Answer 39

polyethylene

Question 40

RADICAL POLYMERIZATION: MECHANISM

Answer 40

1. Initiation
2. Propagation
3. Termination

Question 41

Few radicals are generated on heating _________ to break the weak O-O bond.

Answer 41

benzoyl peroxide catalyst

Question 42

The formed benzoyloxy radical loses _____ and gives a , which adds to the C=C bond of ethylene to start the _________

Answer 42

CO2

phenyl radical (Ph·)

polymerization process

Question 43

Few radicals are generated on heating benzoyl peroxide catalyst to break the weak O-O bond.

The formed benzoyloxy radical loses CO2 and gives a phenyl radical (Ph·), which adds to the C=C bond of ethylene to start the polymerization process.

One electron from the ethylene double bond pairs up with the odd electron on the phenyl radical to form a new C-C bond, and the other electron remains on carbon

Answer 43

initiation

Question 44

The formed carbon radical adds to another ethylene molecule to yield another radical. Repetition of the process for hundreds or thousands of times builds the polymer chain.

Answer 44

propagation

Question 45

The chain process is ended by a reaction that consumes the radical (e.g., combination of two growing chains)

Answer 45

termination

Question 46

(substituted ethylenes) undergo polymerization

Answer 46

vinyl monomers

Question 47

• follows Markovnikov’s Rule
• more highly substituted, secondary radical is formed

Answer 47

RADICALPOLYMERIZATION

Question 48

• predominant alkene synthesis reaction
• from simple precursors
  ◦ alcohols in biological systems
  ◦ either alcohols or alkyl halides in the laboratory
• the opposite of addition of HBr or H2O on an alkene to form an alkyl halide or alcohol
• the loss of HBr or H2O from an alkyl halide or alcohol to form an alkene

Answer 48

ELIMINATION REACTIONS

Question 49

• loss of HX from an alkyl halide
• occurs by reaction of an alkyl halide with strong base e.g., KOH

Answer 49

DEHYDROHALOGENATION

Question 50

carried out by treatment of an alcohol with a strong acid

Answer 50

DEHYDRATION