Removing HX via E2

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Removing HX via E2

• Strong base abstracts H as X- leaves from the
  adjacent carbon.
• Tertiary and hindered secondary alkyl halides
  give good yields.
• Use a bulky base if the alkyl halide usually
  forms substitution products.
  gt

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E2 Diastereomers
?

• Stereospecific reaction (S, R) produces only
  trans product, (R, R) produces only cis.

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SWF Movie
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E2 Cyclohexanes

• Leaving groups must be trans diaxial. gt

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Some Bulky Bases
(CH3CH2)3N triethylamine
gt

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Hofmann Product

• Bulky bases abstract the least hindered H
• Least substituted alkene is major product.

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Removing HX via E1

• Secondary or tertiary halides
• Formation of carbocation intermediate
• Weak nucleophile
• Usually have substitution products too
  
  gt

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Dehydration of Alcohols

• Reversible reaction
• Use concentrated sulfuric or phosphoric acid,
  remove low-boiling alkene as it forms.
• Protonation of OH converts it to a good leaving
  group, HOH
• Carbocation intermediate, like E1
• Protic solvent removes adjacent H
  gt

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Dehydration Mechanism