Notes, Take 2: Amines

Freaking carbonyls are withdrawing groups when attached through the carbonyl carbon, man.


Test Next Tuesday, you forgetful little dweeb.

If you want the survey to shut up, just take it.

Also, study your previous reactions! Don’t get scared by KOH ‘n junk!

Halogenating a ring before doing Friedel-Crafts reactions may reduce reactivity of the ring enough to prevent multiple substitutions.

Amines

So, what the heck is an amine?

  • Derivatives of ammonia (“ammonia, but organicy”)
  • Some of the most important biological compounds, and ones you’ll have to know for biochem
    • Pay attention, self.
  • Usually bases in biological acid/base reactions
  • Vitamin is derived from “vital amine”—a long time ago, someone thought all vitamins had to have amine groups
  • Pharmaceuticals: Prozac, Meridia, Benzedex (and all antihistamines)
    • Marketed as “amine hydrochloride” (amine reacted with HCl) because unprotonated amine groups aren’t very water soluble
    • Also, they smell really bad (like rotting fish)
  • Cedaverine, Putrescine
  • Just Google It

Structure and Classification

  • Amines are classified like alcohols (primary, secondary, tertiary)
  • Naming: Basically, add “amine” (propanamine, 2-propen-1-amine)
  • They’re pretty low on the totem pole, though (only above multiple bonds)
  • When on a chain with a higher priority group, they’re called “amino” groups—don’t forget to designate methyls on the nitrogen with an N
  • Amines can be chiral, but they easily inter-convert (think an umbrella in the wind). If you want to isolate enantiomers, you have to get rid of those dad-gum lone pairs.

Resolution of Enantiomers

  • This is only possible if inversion is slowed or prevented entirely.
  • Exhaustive methylation—use methyl iodide to make a quaternary ammonium salt.
    • If it’s not a quaternary ammonium salt, it can probably interconvert.

Basicity of Amines

  • Amines are bases due to the lone pair of electrons on the nitrogen
  • They’re more basic than alcohols, ethers, or even water
  • Aromatic molecules are less basic than nonaromatic ones
    • As we know, aromatic means acceptance and belonging, which all of us seek
  • Alkyl groups increase basicity until you make a tertiary amine—tertiary amines are sterically hindered
  • Cyclic secondary amines are ridiculously basic in comparison because the alkyl groups can’t “flop around and hide the lone pair”

In imidazole, aromaticity is maintained even when the basic carbon is protonated (sugooooooi!).

Amides aren’t very basic, and they aren’t good nucleophiles.

Preparation

  • Reduction of imines to amineshhhhhhhhhhhhh  roommate misadventures
  • Reduction of amides by LiAlH4
  • Reduction of nitriles to primary amines by LiAlH4
    • Adds a carbon (SN2)
  • Reduction of aromatic nitro groups
    • Iron or tin catalyst with HCl,H2 on Pd, LAH
  • Nucleophilic ring opening of epoxides by ammonia and amines
  • Reduction of alkyl azides by LiAlH4
    • Doesn’t add a carbon (SN2)
  • Akylation of ammonia and amines

So, don’t try to add cyanide or azide to a tertiary alkyl halide. Use NaBH4 to reduce ketones on a nitrated ring.

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