E2, E1

Nucleophilicity vs Basicity
  • Nucleophilicity: kinetic concept, how good at reacting itself
  • Basicity: thermodynamic concept, how badly this reaction would like to happen

(Note), before E1, E2 reactions:
I just realized SN2, SN1, E2, E1 are all talked in high school chemistry. They were not so deep-dived though.

SN2, SN1
Previous: SN2, SN1

SN2 SN1
Rate R = k[electrophile][nucleophile] R = k[electrophile]
Electrophiles ("big barrier") depends on steric hinderance; Primary > secondary > tertiary depends on easiness of carbocation formation; Tertiary > secondary > primary
Nucleophile strong (bearing negative charge) weak (neutral)
Solvent polar aprotic (DMSO/dimethylsulfoxide) polar protic (alcohol, water)
chirality inversion Yes No

E2, E1

E: elimination, of base anion and proton.
Focus on Basicity, no Nucleophilicity.

Both forms a new CC π bond, eliminate a CH proton and a C-(leaving group); also both observe Zaitsev's rule.

How E2/E1 works:

e2-e1.png

Achtung⚠️:

  • E2: leaving Hydrogen must be steric "anti" to leaving group
  • E1: leaving group leaves first, then deprotonation.
E2 E1
Rate R = conc(base)(substrate) R = conc(substrate)
big barrier depends on steric hinderance; Primary > secondary > tertiary depends on easiness of carbocation formation; Tertiary > secondary > primary
Basicity strong weak
Solvent / polar protic: good for ionization
stereo leaving group must anti to hydrogen /

Zaitsev Rule

Elimination reactions usually occur such that they are removing a hydrogen from the carbon attached to the fewest hydrogens.

In Elimination Reactions, The “More Substituted” Alkene Tends To Be The Major Product

Zaitsev.png

(more details to come)
~ Markovnikov rule

E.g. E2, E1
  • E2: 1-bromopropane & sodium methoxide
  • E1: 2-bromo-2-methylpropane & methanol
e2-e1-eg.png

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