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Flashcards in Mechanisms Deck (11)
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1
Q

@E.A

Describe the Two steps

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

3 things to take note for E.A

A
    • ephile always the first to be added to double bond
    • then nucleophile
  1. 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
  2. Carbocation intermediate is trigonal planar
    -> nphile attracted to C+ either side of plane with equal probabilities
    -> chiral C=> racemic mixture
    => equal molar enantiomers
3
Q

@N.S

SN2 mechanism

A

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
4
Q

@N.S

SN1

A

-tertiary RX

  • C-Br bond is broken to form carbocation
  • nucleophile is attracted to C+ to form pdt
5
Q

@E.A

What if the carbon bonded to halogen is chiral?

A
  • 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)
6
Q

Arene@E.S

Why it needs strong electrophile?

A
  • resonance stability as a result of delocalised pi e could of benzene
  • generated with the use of Lewis acid catalyst
7
Q

@E.S

Why benzene does not under no addition?

A

It will cause the disruption of delocalised pi electron cloud

-> lose resonance stability

8
Q

@E.S

Mechanism

A

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.
9
Q

@N.A

Three General steps

A
  1. Partial dissociation of HCN to generate CN-

HCN <=> H+ + CN-

  1. CN- is attracted to C(delta +) to form negatively charged intermediate
  2. The intermediate is protonated to form pdt
10
Q

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

A
  • 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
11
Q

Define free radical

A

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