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