CHEM 2OA3 Lecture Notes - Solvent Effects, Leaving Group, Electronegativity

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Chemical Consequences of Inversion
Retention (invert twice)
Inversion does not necessarily mean R S
Diastereoisomerization
What makes a good L- (A-)?
1. Ability to accommodate e-pair (charge): e-negativity + resonance
2. Size of the orbital describing the e-pair
3. Indirectly: Bond Strength C-L (H-A)
Fluorine is most electronegative element
Iodine is the best leaving group AND nucleophile (in the Halides)
o Increasing size is more important to good leaving group than increasing
electronegativity
Nucleophilicity “Nu”
Affected by charge, basicity, solvent, polarizability, sterics
o Charge (for same atom)
The more charged, the more Nucleophilic
o Basicity (decreases to the right in PT, so does Nu)
As expected, trend opposite L ability
Nucleophilicity doesn’t always track with basicity (basicity decreases as you go down the
PT, but nucleophilicity increases)
o Reason: Solvent effects and polarizability (deformability of orbitals) have a strong
influence
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Document Summary

Inversion does not necessarily mean r s. What makes a good l- (a-): ability to accommodate e-pair (charge): e-negativity + resonance, size of the orbital describing the e-pair, indirectly: bond strength c-l (h-a) Iodine is the best leaving group and nucleophile (in the halides: increasing size is more important to good leaving group than increasing electronegativity. Affected by charge, basicity, solvent, polarizability, sterics: charge (for same atom) The more charged, the more nucleophilic: basicity (decreases to the right in pt, so does nu) Nucleophilicity doesn"t always track with basicity (basicity decreases as you go down the. Pt, but nucleophilicity increases: reason: solvent effects and polarizability (deformability of orbitals) have a strong influence. Protic solvent: solvents with hydrogen attached to electronegative atom (e. g. oxygen: polar ; h2o, roh, r2nh. Solvent shell increases size of the nucleophile, so nucleophilicity increases (going down pt: this stuff is always true in protic solvent, but not.

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