Nucleophile nucleus seeking

1
Nucleophile(nucleus seeking)
A1

• substance that is electron rich, capable of
  donating an electron pair
• attacks substrates at sites of low electron
  density

2
Electrophile
A2

• Substance that accepts electron pairs
• possesses an electron deficient atom
• will attack positions of high electron density

H NO
AlCl
O
Br
BF
3
3
2
3
CO
SO
2
3
3
Mechanism of Reaction
A3

• Double headed arrow represents the movement of a
  pair of electrons
• Step-by-step description of how a chemical
  reaction proceeds

4
Writing Reaction Mechanisms Guidelines
A4

• Arrow always originates from source of electrons
• Head of arrow points to destination of the
  electrons
• Arrows never originate from positive charges(the
  electrons are being moved)
• Account for all charges (ve and -ve)

..
Nu
E
5
Reaction Mechanism Example
A5

• Deprotonation of an alcohol (removal of H)
• (simple organic acid/base reaction)

alcohol
nucleophile (base)
6
Reaction Mechanism Example
A6

• Deprotonation of an alcohol (removal of H)
• (simple organic acid/base reaction)

new bond forming
alcohol
nucleophile (base)
bond breaking
7
Mechanism Deprotonation of Alcohols
A7

• Nucleophile (-OH) attacks the electron deficient
  H (?)
• First arrow directs towards an atom - bond
  formation!
• Second arrow points onto the oxygen ? product
  has oxygen carrying negative charge
• Note Equation is balanced. LHS has 1x -ve
  charge,therefore, products have overall 1x -ve
  charge

8
Mechanism Protonation of an Alcohol
A8
alcohol

• Nucleophilic oxygen attacks electrophilic proton
  (H)

9
Importance of Mechanisms
A9

• Explains reaction pathways
• explores underlying basic principles and enables
  prediction of reaction products
• Can explain stereochemical reaction outcome

10
Importance of Mechanisms
A10

• Explains reaction pathways
• explores underlying basic principles and enables
  prediction of reaction products
• Can explain any stereochemical reaction outcome

O
NaOH
OH
??
NH
2
HCl
??
11
Importance of Mechanisms
A11

• Explains reaction pathways
• Explores underlying basic principles and enables
  prediction of reaction products
• Can explain any stereochemical reaction outcome

12
Importance of Mechanisms
A12

• Explains reaction pathways
• Explores underlying basic principles and enables
  prediction of reaction products
• Can explain any stereochemical reaction outcome

13
Mechanism of Electrophilic Addition
A13

• Electrophilic Addition reaction
• H is the electrophile
• A Markovnikov addition occurs (see 1st year Notes)

14
Mechanism of Electrophilic Addition
A16
step1addition ofH(electrophile) formation
of morestable 2o carbocation

• step2addition ofnucleophile

X
X

• Alkenes are regions of high electron density.
• The electrophile (H) can add to either C1 or C2.
  The more stable product will predominate.
• This mode of addition is known as Markovnikov
  addition

15
Mechanism of Electrophilic Addition
A17
step1addition ofH(electrophile) formation
of morestable 2o carbocation

• step3loss of H

When water is the nucleophile i.e. reaction
conditions are H/H2O