SN1 v SN2: nucleophile and solvent

• is nucleophilic strength involved in SN1 reactions?

  no
• Is weak nucleophile likely to prefer SN1 or SN2?

  Sn1
• what are the two categories for nucleophiles?

  same atom or different atom
• what is a same atom nucleophile?

  Forms the new bond to a carbon over a range of nucleophiles
• what does nucleophiles parallel in same atom nucleophiles?


  Basicity
• what is used to identify the strength of the same atom nucleophile?

  pKa
• Does nucleophilicity parallel basicity of different atom nucleophiles?

  no
• can pKa be used with different atom nucleophiles?

  No
• what is the order or nucleophilic strength of oxyanions?

  OH- > PhO- > AcO- > TsO-
• what influences nucleophilic strength of SN2 for same nucleophile?

  steric hinderance
• what influences nucleophilic strength of SN2 reaction of different nucleophiles?

  atom used
• what are the main factors used involved?

  orbital interaction

  electrostatic attraction
• what type of interaction is dominated by?

  HOMO-LUMO orbital interaction
• SN2 reactions:

  • large atom / orbitals
  • small charge to size ratio
  • not basic
  • high energy HOMO
  • likes to attack saturated C
• compare S to O:

  • larger atom
  • less electronegative
  • e- stabilised by nucleus
  • higher energy HOMO
• Describe when an atom becomes better for SN1:

  • when moving down group
• what is the polarity of solvent related to?

  stabilising polar intermediates
• what solvent for SN1 reaction?

  polar protic solvents both cation and anions
• what part of the molecule does polar protein solvent stabilise?

  delta negative region of carbocation
• what does the delta positive part:

  • stabilise anion/LG
  • prevents anion/LG acting as nucleophile and reforming starting material
• What is the best solvent for SN2 reactions?

  polar aprotic
• Polar aprotic solvent:

  • solvates nucleophile counter-cation
  • naked anion more nucleophilic
  • polar transition state stabilised
• what happens to the delta negative of a polar aprotic solvent?

  solvates cation
• examples of polar aprotic solvent

  • DMSO
  • DMF
  • acetone
• example of polar protic solvent

  • water
  • alcohols
  • acetic acid