Exam 2

Question 1

The abbreviation NAS stands for

Answer 1

Nucleophilic Aromatic Substitution

Question 2

Meisenheimer Complex is formed addition-_______________ mechanism of ______ reaction.

Answer 2

elimination, NAS

Question 3

Benzyne is formed in …………. aromatic substitution reaction.

Answer 3

nucleophilic

Question 4

The state of hybridization of the triple bonded carbons in benzyne is…………….

Answer 4

sp2

Question 5

Phenylation to 1,3-diketo compounds is an example of ……………………reaction.

Answer 5

NAS

Question 6

Give an example with figure (in each case) of terminal alkene, internal alkene, and cycloalkene.

Question 7

Write the structure of zingiberene, (R)- limonene and (S)- limonene.

Question 8

In ethylene, the carbons are…………..hybridized.

Answer 8

sp2

Question 9

Bromination of cis-2-butene produces a racemic mixture whereas trans-2-butene produces a meso compound-why?

Answer 9

Because halogen additions are determined by anti-addition and completely restricted rotation of the carbon-carbon bond of the halonium ion

Question 10

Write the stability order of 1-butene, cis-2-butene, and trans-2-butene

Answer 10

1-butene < cis-2-butene < trans-2-butene

Question 11

Write the chemical structure of DMSO.

Question 12

What is Markovnikov’s rule?

Answer 12

Mark’s rule states that in the addition of (hydrogen halides) to an unsymmetrical alkene, the H atom adds to the more substituted carbon atom— that is the carbon that has the greater number of H atoms to begin with.

Question 13

What is Anti-Markovnikov’s condition? Give an example

Answer 13

-a mechanism that avoids the carbocation intermediate
-the halogen adds to the less substituted carbon.
Ex: addition of hydrogen bromide to propene in the presence of benzoyl peroxide.

Question 14

In the case of hydrohalogenation reaction………………..…..and ………………….….addition occur.

Answer 14

syn; anti

Question 15

What do you mean by vicinal and germinal dihalides? Give example in both cases.

Answer 15

Vicinal: halides are next to each other
Geminal: relationship between 2 atoms or functional groups attached to same atom

Question 16

Vicinal dihalide

Answer 16

when halogens are on adjacent carbons

Question 17

Germinal dihalide

Answer 17

when both halogens are on the same carbon

Question 18

What do you mean by halohydrin? How does it form?

Answer 18

A halohydrin is an organic molecule that contains both a halogen and an OH group.
Halo=halogen and Hydrin=OH.
AKA when a halogen and a hydroxyl are bonded to adjacent carbon atoms

Question 19

How does a halohydrin form?

Answer 19

-Reaction Overview: the halohydrin formation reaction involves breaking a pi bond and creating a halohydrin in its place.
-by treatment of an alkene with a halogen X2 and H2O forms the halohydrin by addition of the elements X and OH to the double bond

Question 20

What is NBS?

Answer 20

N-bromo succinimide is a useful reagent in organic chemistry

Question 21

What purpose does NBS serve in organic synthesis?

Answer 21

(N-bromosuccinimide)
In H2O, NBS decomposes to form Br2, which then goes on to form a bromohydrin in aqueous DMSO by the same reaction mechanism as halohydrin formation
-In other words, Wohl-Ziegler reaction.

Question 22

Hydroboration-Oxidation is an anti………………addition to alkenes.

Answer 22

Markovnikov

Question 23

What is 9-BBN? Mention its use in organic synthesis.

Answer 23

9-boracicyclo[3.3.1] none or
9-BBN is a hydride-bridged primer, which cleaves in the presence of reducible substrates.
-This colorless solid is used in organic chemistry as a hydroboration reagent.

Question 24

Mercurinium ion is formed in………………reaction.

Answer 24

oxymercuration

Question 25

Oxymercuration-Demercuration is a ……………….hydration procedure.

Answer 25

indirect

Question 26

What is the degree of unsaturation?

Answer 26

Degree of unsaturation is the number of pi bonds and/or rings in the molecule

Question 27

Explain the degree of unsaturation considering C6H10 as an example.

Answer 27

-C6H10 has a degree of unsaturation of 2 -this means that C6H10 may contain 2 rings, 2 pi bonds, 1 ring and pi bond, or 1 triple bond

Question 28

Hydrogenation is a ……………addition.

Answer 28

syn

Question 29

Peroxyacetic acid is used in ………………reaction of alkenes.

Answer 29

epoxidation

Question 30

When 2 substituents are added on the same side/face of a double bond

Answer 30

syn

Question 31

When 2 substituents are added on opposite sides/faces of double bond

Answer 31

anti

Question 32

Write the structures of E-3-methyl-2-pentene and Z-3-methyl-2-pentene.

Answer 32

?

Question 33

Explain the terms syn and anti with appropriate examples.

Answer 33

Syn addition is the addition of two substituents to the same side of a double/triple bond, resulting in a decrease in bond order but an increase in number of substituents. Generally the substrate will be an alkene or alkyne. Anti addition: an addition reaction in which two substituents are added to opposite sides of a double bond.

Question 34

…………..is an aliphatic peroxyacid whereas ………………is an aromatic peroxy acid.

Answer 34

peroxyacetic acid; m-chloroperbenzoic acid

Question 35

Draw the orbital diagram of a secondary vinylic carbocation.

Question 36

The product of the reaction between an alkene with HBr is………….whereas the product between the reaction of an alkyne with HBr is…………..

Answer 36

an alkyl bromide; a vinyl bromide

Question 37

What is keto-enol tautomerism? Give an example from nature.

Answer 37

Tautomers are isomers that can convert via migration of a proton, accompanied by a switch of a single bond and an adjacent double bond. Ex: turmeric, as it contains curcumin as an active ingredient

Question 38

What is Lindlar catalyst?

Answer 38

catalyst made from palladium on calcium carbonate that performs the hydrogenation of alkynes in the presence of H2

Question 39

The hydrogenation of an alkyne with Lindlar catalyst produces…………..alkene whereas the treatment with Li/NH3 produces............

Answer 39

cis alkene; trans alkene

Question 40

Write the structure of a secondary vinylic carbocation.

Question 41

Carbon dioxide is produced as a byproduct during oxidative cleavage of …………..alkynes.

Answer 41

terminal

Question 42

Write the name of four strong oxidizing reagents.

Answer 42

O3-ozone KMNO4-potassium permanganate H2O2-hydrogen peroxide HNO2-nitrous acid

Question 43

Acetylide anion is formed on the treatment of…………………..with acetylene.

Answer 43

a strong anhydrous base

Question 44

Isomeric compounds that rapidly interconvert by the movement of a ………………. are called………..

Answer 44

proton; tautomers

Question 45

Treatment of an alkene with a halogen X2 and H2O forms …………………….

Answer 45

halohydrin

Question 46

Nucleophilic aromatic substitution can occur when……………… groups are ortho or para to the halogen atom.

Answer 46

strong electron withdrawing group

Question 47

Nature produces ……….. alkene exclusively and Oils are derived from ……… having a larger number of double bonds.

Answer 47

cis; fatty acids

Question 48

The addition of HBr to an alkene generates ………………carbocation whereas …………..carbocation is generated during the addition of HBr to an alkyne.

Answer 48

an alkyl secondary carbocation; a vinylic secondary carbocation

Question 49

Which of the following compounds is least reactive towards NAS?

Answer 49

1-bromo-3-nitrobenzene

Question 50

Formula for degree of unsaturation?

Answer 50

(2n+2) - x / 2

Question 51

C44H64O2

Answer 51

Crocin

Question 52

Translate this to form where degree of unsaturation can be calculated: C6H5N

Answer 52

C6H4

Question 53

Translate this to a form where degree of unsaturation can be calculated: C6H5NO2

Answer 53

C8H12

Question 54

Translate this to a form where degree of unsaturation can be calculated: C9H16Br2

Answer 54

C9H18

Question 55

Translate this to a form where degree of unsaturation can be calculated: C10H12N2O3

Answer 55

C10H10

Question 56

Translate this to a form where degree of unsaturation can be calculated: C20H32ClN

Answer 56

C20H32

Question 57

Translate this to a form where degree of unsaturation can be calculated: C44H64O2+

Answer 57

C44H64

Question 57

What are the basic differences between SNAr reaction with SN1 and SN2 reactions?

Answer 57

SN1/SN2 = alkyl halides SNAr = dissociation & stable carbocation SN2 = Nu back attacks as LG leaves SNAr = flat ring so no back attack & no dissociation addition-elimination = meisenheimer elimination-addition = benzyne intermediate

Question 58

Use chlorobenzene as an example for why SNAr reactions are not considered either SN1 or SN2

Answer 58

-chloronbenzene and SN1 not happen bc a positive charge is created on the ring; -chlorobenzene is not an SN2 reaction bc steric hindrance is created. SNAr will bc if strong EWG at ortho/para through addition elimination = Meisenheimer complex

Question 59

What is benzyne?

Answer 59

intermediate formed in elimination-addition reaction; when there is no EWG

Question 60

Why 2-chloropropane is formed as the sole product in the reaction between propene and HCl? Explain with mechanism.

Answer 60

propene is unsymmetrical to MKV rule = H-less substituent

Question 61

Why secondary carbocation is more stable than primary carbocation? Explain the details.

Answer 61

Secondary carbocation has lower activation energy so a faster reaction & lower effect

Question 62

Discuss the mechanism (drawing is essential) of the electrophilic addition of water to 1-methylcyclohexene.

Answer 62

hydration-electrophilic addition of water; pi bond attacks H3O+; electrophile added to pi bond; formed carbocation; Nu (H2O) attacks carbocation; water removes proton & forms alcohol; acid catalyzed

Question 63

How TMBE can be synthesized from the electrophilic addition of alcohol to alkenes?

Answer 63

tert-butyl methyl ether; ELECTROPHILIC ADDITION; methanol and 2-dimethylpropene; catalyzed by H2SO4; MKV rule

Question 64

Draw and explain the mechanism of bromination of cis-2-butene

Answer 64

halogenation; electrophile added to pi bond; breaks/forms 4 bonds = rate determining.; bridges bromonium ion; nucleophilic attacks ion; racemic mixture with cis bc added anti

Question 65

Why is hydroboration regioselective? Explain the mechanism considering hydroboration-oxidtion reaction to propene.

Answer 65

steric factor & electronic/inductive effects; BH3 added to alkene, large group to less hindered & adjacent methyl stabilizes partial positive charge

Question 66

Explain the stepwise mechanism of the reaction between mercury (II) acetate to ethylene.

Answer 66

mercury (II) acetate dissociates = +Hg(OAc); attacks pi bond and forms mercurinium ion; water approaches ion from anti to ring; MKV = water added to more substituted

Question 67

What is ozonolysis? Explain with stepwise mechanism.

Answer 67

oxidative cleavage of alkene to carbonyl; pi and sigma bonds broken & replaced with C=O bonds; ozone has both nucleophilic and electrophilic capabilities

Question 68

Explain with suitable examples the concept of E- and Z- alkenes. Is there any difference between cis/trans with E/Z? Justify your answer.

Answer 68

when 3 or 4 different groups use E/Z instead of cis/trans; visually split double bond and asses priority of each side E = higher priority on opposite sides Z = higher priority on same side

Question 69

Cis-2-butene has a higher boiling point (40C) than trans-2-butene (10C) - explain

Answer 69

2 methyls on same side of cis form net dipole moment; polar = higher bp

Question 70

How can you correlate the melting points of oleic acid, linoleic acid, and linolenic acids with their double bonds?

Answer 70

fatty acid w same number of C that increases in double bonds = mp decreases

Question 71

What is mercurinium ion? When does it form?

Answer 71

it is a cyclic intermediate with + charge; results from + Hg(OAc) reacting with alkene; oxymercuration rxn

Question 72

What is keto-enol tautomerism? Explain with the example of curcumin.

Answer 72

enols rearrange to form ketones through movement of proton from OH to alkene carbon; ketone more stable

Question 73

Hydration of terminal alkynes in the presence of mercuric sulfate always yields a methyl ketone whereas hydration of internal alkynes produces mixture of ketones. Explain with appropriate example.

Answer 73

terminal = methyl ketone bc addition of water is MKV

Question 74

Hydroboration-oxidation of an internal alkyne produces ketone whereas the same reaction for a terminal alkyne yields aldehyde-why? State the rule associated with this.

Answer 74

anti-MKV bc of the way H2O is added

Question 75

Oxidation (KMnO4 or ozone) of unsymmetrical internal alkynes produces two carboxylic acids whereas under the same condition terminal alkyne produces one carboxylic acid. Explain

Answer 75

terminal alkynes oxidize and form carboxylic acid and CO2

Question 76

Write the (i) reagents and (ii) mechanistic steps and (iii) explanation associated with the following reaction:

Answer 76

i.) 6-C alkyne, NaNH2, NH3, alkyl halide ii.) produce hydrocarbon that leads to larger alkynes; acetylide anion reacts with alkyl halide; transition state until halide leaves; inversion of configuration since SN2