topic 10 and 20 Flashcards

1
Q

what evidence suggested against the model by kebulé

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

what type of reaction do you get from benzene

A

substitution

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3
Q

no. of delocalized e- in benzene

A

6

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4
Q

what does benzene react with

A

electrophiles

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5
Q

what does an optically active compound do

A

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

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6
Q

which types of isomers are always optically active

A

enantiomers

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7
Q

what are enantiomers

A

non-superimposable images of each other

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8
Q

racemic mixture

A

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

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9
Q

outline the formation of nitrobenzene

A

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

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10
Q

conditions for nitrobenzene formation

A

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

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11
Q

outline what an arene compound is

A

hydrocarbon with alternating double and single bonds forming rings

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12
Q

outline how nitrobenzene is converted to phenylamine

A
  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)
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13
Q

why doesnt benzene readily undergo addition reactions

A

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

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14
Q

resonance stability energy

A

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

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15
Q

chlorination of benzene

A

AlCl3 catalyst in dry ether to form chlorobenzene

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16
Q

conditions for OH as a nucleophile

A

heat, NaOH (aq)

17
Q

conditions for Nh3 as a nucleophile

A

conc. NH3, heat in a sealed tube

18
Q

product of a halogenoalkane and NH3

A

amine + HX

19
Q

what can the product of NH3 nucleophilic substitution do,

A

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

20
Q

conditions of CN- as a nucleophile

A

KCN (aq), methanol, heat under reflux

21
Q

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

A

to increase the carbon chain length

22
Q

why is sn1 a faster reaction than sn2

A

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

23
Q

molecularity

A

number of molecules that take part in the rate determining step

24
Q

why cant tertiary alcohols undergo oxidation

A

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

25
what is the observed color change for the oxidizing agent in nucleophilic addition
orange to green
26
what is the change in oxidation state for the oxidizing agent (acidified potassium dichromate)
+6 to +3
27
explain why alcohols have a higher melting and boiling point than alkanes of similar Mr value
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
28