topic 10 and 20

Question 1

what evidence suggested against the model by kebulé

Answer 1

1. bond angles and bond lengths are all equal
2. number of isomers
3. no addition rxns
4. enthalpy of hydrogenation was less exothermic

Question 2

what type of reaction do you get from benzene

Answer 2

substitution

Question 3

no. of delocalized e- in benzene

Answer 3

6

Question 4

what does benzene react with

Answer 4

electrophiles

Question 5

what does an optically active compound do

Answer 5

rotate the plane of polarized light as it passes through a solution of the compound

Question 6

which types of isomers are always optically active

Answer 6

enantiomers

Question 7

what are enantiomers

Answer 7

non-superimposable images of each other

Question 8

racemic mixture

Answer 8

a mixture containing both enantiomers in equal amounts and it is optically inactive

Question 9

outline the formation of nitrobenzene

Answer 9

conc h2so4 and hno3 to form the catalyst (NO2+) which is attracted to the high e- density of delocalized pi bonds of benzene. the e- go to form a bond with the electrophile, but H is still bonded, so the delocalized pi system is partially broken and has a partial positive charge. the intermediate then loses the H+ and the e- from the C-H bond restore the delocalized pi system

Question 10

conditions for nitrobenzene formation

Answer 10

heat under reflux at 50 deg C to overcome the high Ea, conc h2so4 and hno3

Question 11

outline what an arene compound is

Answer 11

hydrocarbon with alternating double and single bonds forming rings

Question 12

outline how nitrobenzene is converted to phenylamine

Answer 12

1. reduction, Sn and conc.HCl, to produce the phenylammonium ion C6H5NH3+
   2.free the NH2 group by deprotonating the ion by reacting it with NaOH (aqueous)

Question 13

why doesnt benzene readily undergo addition reactions

Answer 13

an addition reaction would destroy the delocalized system and the stability associated with it

Question 14

resonance stability energy

Answer 14

delocalization of electrons, as opposed to alternate single and double bonds, leads to increase in stability

Question 15

chlorination of benzene

Answer 15

AlCl3 catalyst in dry ether to form chlorobenzene

Question 16

conditions for OH as a nucleophile

Answer 16

heat, NaOH (aq)

Question 17

conditions for Nh3 as a nucleophile

Answer 17

conc. NH3, heat in a sealed tube

Question 18

product of a halogenoalkane and NH3

Answer 18

amine + HX

Question 19

what can the product of NH3 nucleophilic substitution do,

Answer 19

act as another nucleophile and react with more reactant to produce a secondary amine (diethylamine)

Question 20

conditions of CN- as a nucleophile

Answer 20

KCN (aq), methanol, heat under reflux

Question 21

in industry, what is the purpose of reacting potassium cyanide with bromoethane

Answer 21

to increase the carbon chain length

Question 22

why is sn1 a faster reaction than sn2

Answer 22

the formation of the transition state in sn2 is thought to have higher activation energy than the formation of the carbocation in sn1

Question 23

molecularity

Answer 23

number of molecules that take part in the rate determining step

Question 24

why cant tertiary alcohols undergo oxidation

Answer 24

the cabron attached to the OH group is fully substituted and is not attached to any H’s

Question 25

what is the observed color change for the oxidizing agent in nucleophilic addition

Answer 25

orange to green

Question 26

what is the change in oxidation state for the oxidizing agent (acidified potassium dichromate)

Answer 26

+6 to +3

Question 27

explain why alcohols have a higher melting and boiling point than alkanes of similar Mr value

Answer 27

similar Mr value means that the alcohol and alkane will have a similar number of e- therefore similar London forces; BUT alcohols also have hydrogen bonds which require more energy to overcome