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Flashcards in Mechanisms Deck (11):


Describe the Two steps

1. Alkene pi e are attracted to delta+ to form carbocations intermediate

2. Delta- is attracted to C+ to form pdt


3 things to take note for E.A

-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



SN2 mechanism

-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




-tertiary RX

•C-Br bond is broken to form carbocation

•nucleophile is attracted to C+ to form pdt



What if the carbon bonded to halogen is chiral?

-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)



Why it needs strong electrophile?

-resonance stability as a result of delocalised pi e could of benzene

-generated with the use of Lewis acid catalyst



Why benzene does not under no addition?

It will cause the disruption of delocalised pi electron cloud

-> lose resonance stability




•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.



Three General steps

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


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

•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


Define free radical

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