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Week 4: Organic Reactions (3 types (Elimination: One reactant splits into…
Week 4: Organic Reactions
3 types
Substitution:Two reactants exchange groups/atoms to form two products
Elimination: One reactant splits into two products
Some groups are removed from the saturated reactant, forming unsaturated multiple bond in the product.
Addition: Two reactants add together to give one product
The unsaturated multiple bond in one reactant is added with another reactant,producing saturated single bonds in the product.
How they occur, described by Reaction Mechanism (Arrow pushing)
Involves Electron Transfer: breaking and forming bonds
Have 2 ways
Radical Reactions: Homolytic bond breaking & homogenic bond formation
(shown by) Half curly arrow: Indicates transfer of 1 electron
Homolytic bond breaking:
Bond breaking in which the bonding electrons are evenly divided between the two parting atoms/ groups
Free radicals: reactive intermediates with one unpaired electron
neutral, unstable, short half life and highly reactive
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Homogenic bond formation:
Bond formation in which each joining fragment contributes one electron.
free radicals with one unpaired electron that can form new bond each
Polar reactions:
Heterolytic bond breaking & heterogenic bond formation
(shown by) Curly arrow: Indicates transfer of 2 electrons
Heterogenic bond formation
:
electron-rich reactant donates pair of electrons to electron-poor reactant
Preparation of alkenes
Using haloalkanes and base; Haloalkanes (halogen substituted alkane) undergoes elimination reaction in the presence of NaOH (strong base) to give alkenes
eliminate
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Using alcohols and acid: Alcohols (OH substituted alkanes) undergoes elimination reaction in the presence of H2SO4 (strong acid) to give alkenes
eliminate
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Heterolytic bond breaking
:
Bond breaking where the bonding electrons are unevenly divided between the two parting atoms i.e. one of the fragments leaves with both electrons
Result in charged species (cation and anion)
Carbocation: Carbon cation. Positively charged intermediate
Carbocations and anions are highly reactive and have short half lives
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Anion: Negatively charged intermediate
Occurs at molecules with Reaction Sites that react with each other
Nucleophile aka Lewis Base: Electron rich region in a molecule that donates electron
Multiple bonds: pi electrons are more available to donate to electron poor species
Species with lone pair of electrons
Negatively charged species
Electrophile aka Lewis Acid: Electron poor region in a molecule that accepts electron
positively charged species
Species with vacant orbital
Polar bonds: uneven sharing of electrons results in one atom being “partially positive