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Steric Hindrance Issues

Steric Hindrance Issues. Sites that are sterically hindered can be blocked and may undergo very little substitution. These include: - a site that has two ortho substituents - a site that is ortho to one very bulky group. Example: two ortho substituents.

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Steric Hindrance Issues

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  1. Steric Hindrance Issues Sites that are sterically hindered can be blocked and may undergo very little substitution. These include: - a site that has two ortho substituents - a site that is ortho to one very bulky group Example: two ortho substituents The site between –CH3 and –Cl is crowded.

  2. Steric Hindrance Issues Sites that are sterically hindered are be blocked and may undergo very little substitution. These include: - a site that has two ortho substituents - a site that is ortho to one very bulky group Example: ortho to a bulky group (such as isopropyl or t-butyl) The site next to t-butyl is crowded.

  3. Substitution Reactions - Practice Predict the major product for the following reactions.

  4. 16.3 Alkylation of Aromatic Rings EAS Reactions - use electrophiles like NO2+ or Br+ : Can we add an alky group ( -R), via a carbocation “R+”?

  5. Ring Alkylation – Friedel-Crafts Reaction R-Cl + AlCl3 R+ + AlCl4- Aromatic substitution of an alkyl for an -H Catalyst: AlCl3 Aluminum chloride promotes formation of the carbocation

  6. Limitations of Friedel-Crafts Alkylation • Only alkyl halides can be used (F, Cl, I, Br) • Aryl halides and vinylic halides do not react (their carbocations are too hard to form)

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