Topics
Alkenes:
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Structure and Bonding
o C=C, 1 σ, 1 π, more reactive
Isomerism
o Cis-trans due to rigidity of double bond
Naming
o -ene
Reactions
o Hydrogenation
 Addition of H2 to form alkanes (reduction)
o Electrophilic addition
 Addition of HX (halogen) to form alkyl halides (haloalkane)
o Hydration
 Addition of H2O to form alcohols
o Halogenation
 Addition of halogens to form dihalides
o Oxidation
 Formation of epoxides, diols and cleavage products
Alkynes
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Structure and Bonding
o C≡C, 1 σ, 2 π, very reactive
Acidity
o Terminal alkynes have relatively acidic H atoms -> deprotonated to
form carbanions
Naming
o -yne
Reactions
o Hydrogenation
 Addition of H2 to form alkanes/alkenes
o Electrophilic addition
 Addition of HX and halogens to form haloalkenes and
dihaloalkanes
o Hydration
 Addition of H2O to form ketones or aldehydes
o Oxidation
 Formation of diketones and cleavage products
Aromatic Compounds (Arenes)
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Structure and stability
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o Benzene – simplest, delocalised π-electron system that provides
stability (resonance energy)
Reactions
o Electrophilic substitution
 Nitration, halogenation, alkylation, acylation (friedel-crafts)
 Formation of carbocation intermediate, loss of proton
Spectroscopy
o Infra-red spectroscopy
 Measures bond vibrations
o Ultraviolet spectroscopy
 Measures electronic transitions; π to π* transitions in alkanes
Regiochemistry of Elimination
 Zatisev’s Rule
o When multiple products can be formed, the more substituted
(hydrogen for another group) alkene is usually the major product
(E1 and E2 mechanisms)
 E1 mechanism
o Not stereospecific, H2 does not need to be anti-periplanar to the
leaving group
 E2 mechanism
o H2 must be anti-periplanar to the leaving group, more controlled
regioselectivity
E1 mechanism:
 Formation of carbocation (leaving group departs forming carbocation)
E2 mechanism:
 Anti-elimination
 Concerted step (base removes proton, leaving group departs
simultaneously, forming double bond)
E1cb mechanism:
 Formation of carbanion (base removes a proton, forming carbanion
intermediate)
 Departure of leaving group (leaving group departs, forming double
bond)