Mechanisms

Question 1

@E.A

Describe the Two steps

Answer 1

1. Alkene pi e are attracted to delta+ to form carbocations intermediate
2. Delta- is attracted to C+ to form pdt

Question 2

3 things to take note for E.A

Answer 2

1. • ephile always the first to be added to double bond
   • then nucleophile
2. HX added to unsymmetrical
   -Maj: ephile added to C with most H
   -> resulting carbonation has more e-donating alkyl gps
   => dispense the positive charge therefore more stable
3. Carbocation intermediate is trigonal planar
   -> nphile attracted to C+ either side of plane with equal probabilities
   -> chiral C=> racemic mixture
   => equal molar enantiomers

Question 3

@N.S

SN2 mechanism

Answer 3

For
-methyl/Pri RX

• nucleophile is attracted to C(delta+) from side opposite of C-Br bond
• > pdts with inversion of configuration about the C atom

Question 4

@N.S

SN1

Answer 4

-tertiary RX

• C-Br bond is broken to form carbocation
• nucleophile is attracted to C+ to form pdt

Question 5

@E.A

What if the carbon bonded to halogen is chiral?

Answer 5

• nucleophile can be attracted to the trigonal planar carbocation from either side of the plane with equal probabilities
• > equal amt of 2 enantiomers (racemic mixture)

Question 6

Arene@E.S

Why it needs strong electrophile?

Answer 6

• resonance stability as a result of delocalised pi e could of benzene
• generated with the use of Lewis acid catalyst

Question 7

@E.S

Why benzene does not under no addition?

Answer 7

It will cause the disruption of delocalised pi electron cloud

-> lose resonance stability

Question 8

@E.S

Mechanism

Answer 8

Either
•HNO3 + H2SO4 <=> NO2+ + HSO4- + H2O
(c.HNO3 and H2SO4 react to geerate NO2+)

•AlCl3 + Cl2 -> Cl+ +AlCl4-
(lewis acid cat reacts with Cl2 to generate Cl+)

• pi e- colud is attracted to e-phile to form positively charged arenium ion
• H is abstracted from the arenium ion by AlCl4-/HSO4_ to restore the aromaticity of the benzene ring to from pdt and to regenerate the cat.

Question 9

@N.A

Three General steps

Answer 9

1. Partial dissociation of HCN to generate CN-

HCN <=> H+ + CN-

2. CN- is attracted to C(delta +) to form negatively charged intermediate
3. The intermediate is protonated to form pdt

Question 10

Why pdt of N.A does not rotate the plane polarised light

Answer 10

• CN- can be attracted to trigonal planar carbonyl C from either sides of the plane with equal probabilities
• forming an equal amt of two enantionmers (racemix mixture) if aldehydes and unsymmetrical ketones are reacted with HCN

Question 11

Define free radical

Answer 11

Atom with an unpaired e formed from homolytic fission of a covalent bond