Nuc Substitution Flashcards
How would you classify a carbonyl carbon?
- weak electrophile
- has partial pos and partial negative components, inductive effect of Oxygen pulls EN
Can a pi bond be a nucleophile? why or why not?
- electrons in double or triple bond can be donated to form new covalent bond
- usu weak nucleophile
What kind of nucleophile is Ammonia and why?
strong: because nitrogen is not very inductive/EN element, does not pull too strongly on the lone pair
- thus lone pair can readily leave/react with another species
All lewis bases are:
nucleophiles
- conjugate base is an electron donor
All lewis acids are:
electrophiles
- conjugate acid is an electron acceptor
SN1 vs SN2 definition difference
- depends on reaction rate
- 1: concentration of one reactant
- 2: concentration of two reactants
SN1 in depth
- LG leaves before anything else > gen carbocation (slow)
- RLS: carbocation formation and dependent on conc of substrate only
- Nuc attack: carbocation strong electrophile by nuc (OH, H2O) > deprotonated
- product loses chirality and will be 50% race mixture
- 2 steps
SN2 in depth
- depends on conc of nucleophile and substrate
- common substrate: alkyl halide (carb-halogen, partial pos charge)
- must be backside attack > as far away as possible from halide
- chirality of substrate will be inverted with LG removal
- 1 driven step
Promoting SN1
- formation of carbocation
- what increases stability: degree of sub of alkyl groups
- tertiary: most stable or secondary
- need a good LG attached to secondary or tertiary
- weak nucleophile is fine, solvent plays good role
- polar protic solvent: form H-bonds, highly EN (O, N)
- water, methanol, ethanol > help stabilize carbocation
- common water to be nuc and solvent
Promoting SN2
- promote nuc atttack, aggressive nuc
- reach electrophilic carbon: steric hindrance
- thus STRONG AND SMALL, non bukly substrate
- methyl and primary carbons, opposite of SN1
- Polar aprotic: also opp: lacksacidic hydrogens
- solvent: Acetone, DMSO (dont affect Nuc)
Fischer esterification
- acid catalyzed sub Rx takes place at carbonyl carbon
- COOH > ester
Fischer esterification mechanism
- start COOH: add strong acid for protonation
- alcohol O attacks carbonyl C > more electrophilic
- add OH: nucleophile, attack electrophile on carbonyl carbon
- two OH and alcohol on intermdiate, proton lost to conjuate base
- protonation of OH
- OH2 group leaves
- other OH send electrons to reform carbonyl > deprotonation
- ester formed: R-C=OOR
- LG and nuc: similar ROH and Water
- hydrolysis added to break it down
- hydrolysis ester is fischer esterification in reverse
- Ester broken down into COOH and alcohol
Imine formation
- usu Ketone + amine = imine: C=N
- nuc 2 attacks on carbonyl carbon > tetrahedral intermediate, N temporary pos charge, nuc again
