Chemical Reactivity

Question 1

How is a carbocation formed

Answer 1

Through heterolytic bond cleavage

Question 2

What are the ways of stabilizing a carbocation

Answer 2

1) Inductive effect of more alkyl groups attached to the alpha carbon
2) hyperconjugation of P orbital and sigma orbitals
3) stabilization of less structural inhibitors to the trigonal planar carbocation
4) resonance, conjugating double bonds
5) rearrangement of hydrogen or a methyl group to increase hyperconjugation and inductive effect

Question 3

Does addition of hydrogen halide via electrophile addition to alkenes show regioselectivity

Answer 3

Yes

Question 4

Where is the hydrogen placed according to Markovnikov’s rule

Answer 4

On the least substitution carbon

Question 5

What needs to happen to water for addition of H, OH via electrophile addition to alkenes to occur fast enough

Answer 5

Water must be acidified to a hydronium ion catalyst

Question 6

Is addition of H, OH via electrophile addition to alkenes regioselective

Answer 6

yes

Question 7

Is addition of di-halogens via electrophile addition to alkenes stereoselective

Answer 7

no, it is stereospecific

Question 8

What is the intermediate for a hydro-bromo addition

Answer 8

A bromonium ion

Question 9

What is the intermediate for a hydro-chloro addition

Answer 9

Chloronium ion and also a carbocation. This is because chlorine is a smaller atom

Question 10

What are the regioselectivity and stereoselectivity of addition of OHBr via electrophile addition to alkenes

Answer 10

• regioselective, depending on what side of the bromonium ion would be more likely to stabilize a carbocation
• stereospecific with bromonium ion

Question 11

What is the product of dihydroxylation via electrophile addition to alkenes

Answer 11

Stereospecific product with syn addition

Question 12

What is the reagent used for dihydroxylation via electrophile addition to alkenes

Answer 12

OSO4 or MnO4-

Question 13

What is the non Markovnikov way of adding electrophiles to alkenes

Answer 13

Hydroboration-oxidation

Question 14

What is the reagent used for non Markovnikov addition of electrophiles to alkenes

Answer 14

Borane (BH3)

Question 15

Does non Markovnikov addition of electrophiles to alkenes result in anti addition or syn addition

Answer 15

Syn

Question 16

What reagent is used for non Markovnikov addition of electrophiles to alkynes

Answer 16

SIA

Question 17

What reagent is required for acid catalyzed hydration of terminal alkynes

Answer 17

H2SO4 and HgSO4

Question 18

What is a cool property of the acid catalyzed hydration of terminal alkynes product

Answer 18

The product that is a enol quickly converts to a Ketone via tautomerism

Question 19

What is Sn2 reaction mechanism

Answer 19

Sn2 means substitution nucleophile bimolecular reaction. Occurs in one step through a transition state and backside attack

Question 20

What solvent is best for Sn2 reactions

Answer 20

Polar aprotic solvents

Question 21

What is Sn1 reaction mechanism

Answer 21

Sn1 means substitution nucleophile unimolecular that happens in two steps through a carbocation

Question 22

What solvent is best for Sn1 reactions

Answer 22

Polar protic solvents

Question 23

What is beta elimination

Answer 23

This competes with substitution and involves loss of hydrogen from a beta carbon and halogen from the alpha carbon to form alkene

Question 24

What does E2 compete with

Answer 24

both Sn1 and Sn2

Question 25

What is the major product for formation of alkenes

Answer 25

The one with the more substituted carbons

Question 26

What is the major product for formation of alkenes in cyclic compounds

Answer 26

More conjugation

Question 27

What is required for substitution into cyclic compounds

Answer 27

Leaving group and hydrogen must be trans and co-planar

Question 28

What reagent is needed to turn alcohols into alkenes by dehydration elimination

Answer 28

Strong acid such as H2SO4

Question 29

What alcohols undergo E1 eliminations

Answer 29

Secondary and tertiary

Question 30

What alcohols undergo both E1 and E2

Answer 30

primary alcohols

Question 31

What reagents are good oxidisers

Answer 31

KMNo4 and K2CrO7

Question 32

What happens when alcohol is oxidised

Answer 32

It might further oxidize to carboxylic acid from an aldehyde

Question 33

What reagent can stop aldehydes from further oxidizing to a carboxylic acids

Answer 33

PCC

Question 34

What are some reducing agents for hydrogenation

Answer 34

-H2 gas and metal catalyst
- NaBH4
- lindlar
- SMEAH

Question 35

What sort of electrophilic reaction do cyclic molecules undergo

Answer 35

Substitution

Question 36

what is a closed loop

Answer 36

(2n+4)pi electrons where n is integer

Question 37

What does ortho mean

Answer 37

one carbon apart

Question 38

what does meta mean

Answer 38

two carbons apart

Question 39

what does para mean

Answer 39

opposite sides of the aromatic ring

Question 40

What would happen if aromatic rings undergo addition

Answer 40

an extra bond means it will no longer be aromatic

Question 41

What are the 3 basic steps to aromatic electrophilic substitution

Answer 41

1) Formation of the electrophile
2) Formation of new covalent bond to make a resonance stabilized carbocation
3) removal of H+ to regain aromaticity

Question 42

What are some issue with alkylated benzene

Answer 42

• highly reactive so will likely go on to further react and add more alkyl groups
• carbocation has rearrange

Question 43

What is an issue with either alkyl and acyl groups on benzene

Answer 43

if benzene already has a strong electron withdrawing group then the reaction won’t occur