medchem 7 , 8

Question 1

the structure and properties of benzene

Answer 1

• colorless , toxic cariogenic, liquid at boiling point of 80 c
• have 6 carbons and hydrogens attached to each carbon
• c-c bond are equal to: 139 between single and double bond length
• no formal single or double bonds
• molecular formula C6H6
• aromatic

Question 2

benzene is a — of these resonance structure

Answer 2

resonance hybrid and individual resonance are imaginary and not real

Question 3

each carbon in the benzene has — orbital and has — with its electrons sideways and each pi cloud contains — electron

Answer 3

2p , aromatic sextet or aromatic cloud , 6 pi electrons

Question 4

huckles rule of aromaticity states,
to have an aromatic compound it must have —- each atom in the ring has — and there is —

Answer 4

• planer ring
• pz orbital
• (4n + 2) pi n= integer

Question 5

benzene aromatic stability can be measured by

Answer 5

• heat of hydrogenation ( aka the addition of h2 to a double bond )
• more stable, less reactive due to the release of energy in the aromatic ring

Question 6

benze has — times the cylohexene value

Answer 6

3 times as there is 3 double bonds
- more bonds , more stability

Question 7

substation in the benzene can be :

Answer 7

• ortho: groups r close
• meta : groups r one unit apart
• para : groups are 2 units apart

Question 8

many drugs are — derivatives

Answer 8

benzene and synthesised from Benzene or substuited benzene

Question 9

reactions of benzene:
elctrophilic substution - electrophiles react w electron rich aromatic ring as:

Answer 9

-chloloration
- beneze + cl2
- catalyst: AlCL3 or FeCl3
- products: chlorobenze and hcl
- fe2 reacts violently without a catalyst
- br2 reacts in the presence of AlBr3
- no light needed , not a free radical mechanism

Question 10

steps of the chlorination of benzene

Answer 10

• generation of the electrophile
• reaction between the ring and the electrophile aka one bond forming and the other is breaking
• loss of h+ in the carboncation
• regeneration of the catalyst.

Question 11

is carbonation aromatic

Answer 11

NO

Question 12

AlCl3 is a – and cl- is —-

Answer 12

Lewis acid aka elctron acceptor
Lewis base electron pair donor
( bf3 and group 3 are all lewis acids since they have 6 electrons )

Question 13

the driving force in the loss of H to remove the carbonation is from

Answer 13

regeneration of aromaticity which accounts for the mechanism pathway

Question 14

reactions of alkylation in benzene don’t occur in

Answer 14

cholorbezene or halides that are directly attached to the carbon

Question 15

example of alkylation of benzene:

Answer 15

benze + ch3-cl
- generetion of an electrophile = ch3-

Question 16

nitration of benzene
- sulphuric acid H2SO4 will — the nitric acid HONO2
- the nitric acid will lose — and become — aka an —

Answer 16

• protonate
• h20
• nitronium ion
• electrophile
• its isolectronic w/ c02

Question 17

bromination of benzene steps

Answer 17

• generation of electrophile ( AlBr3 + br-br ) –> br- + AlBr4 +
• formation of non aromatic carbonation
• aromaticity is gained
• albr4 - + h+ –> albr3 + hbr

Question 18

the carboncation resonances forms differ in

Answer 18

• position of the +ve charge and the double bond
• this gives the carboncation the stability but it’ll still lose the proton
• more stability is gained by the formation of the aromatic ring again

Question 19

the number of resonance structures in carboncation

Answer 19

• 3
• and they are formed by the spread of the +ve charge

Question 20

substuited benzes can undergo

Answer 20

electrophilic substuited reactions

Question 21

the rate of reaction, products, and what position the ring depends on

Answer 21

the X that is substuited in the ring

Question 22

electron — groups make the ring more electron rich , more attractive to electrophile and is faster

Answer 22

donating

Question 23

example of electron donating groups

Answer 23

ch3

Question 24

another name for electron donating groups

Answer 24

activators

Question 25

electron --- groups make the ring more electron poor and less reactive and slower

Answer 25

withdrawing

Question 26

another name of electron withdrawing groups

Answer 26

deactivators

Question 27

cl and no2 are an example of

Answer 27

electron withdrawing groups

Question 28

why are oh and nh2 groups strongly activating

Answer 28

- bc of the lone pair overlaps with the aromatic ring making it more electron rich - aka they are electron donating groups

Question 29

electron donating groups are ---- directors

Answer 29

ortho, para - the +ve sign needs to be next to the original substituent

Question 30

electron dontating stabilise the

Answer 30

2 intermediate of the carboncation in ortho or para position and teriatry is more stable than secondary

Question 31

electron --- groups are meta directing

Answer 31

withdrawing

Question 32

electron withdrawing destabilise the carboncation in --- and -- position but favours ---

Answer 32

- ortho, para - meta

Question 33

--- are electronegative and are electron withdrawing but they are able to donate a pair or electrons and form --- . they are --- by conjunction and --- by inductive effect

Answer 33

- halogens - resonance - donating - withdrawng - favours ortho, para

Question 34

all ortho and para are activating groups and are electron donating except

Answer 34

halogens

Question 35

ch3 and alkyls are

Answer 35

weak activators

Question 36

halogens are

Answer 36

deactivators

Question 37

nh2 and oh are

Answer 37

strong activators

Question 38

n02 , s03h , CF3 , NH3 , C triple bond N , cooh , coor are

Answer 38

strong deactivators as they r elctrongevative or have +ve charge

Question 39

in halogenation, Tulane + cl2 with no catalyst will become

Answer 39

- ch2cl + hcl - toluene here acts as a substuieted alkane and free radical reaction so its not electrophilic subsetution

Question 40

check slide 20

Question 41

the type of reactions bezene undergo is ---

Answer 41

electrophilic substitution