Exam 2 Flashcards
How much more stable are conjugated dienes than isolated dienes?
** Because of resonance!!! **
Conjugated dienes are 27 kJ/mol more stable than isolated dienes
Examples of EWG
Aldehydes, Ketones, Esters, Amides, Carboxylic Acids, Nitriles, Nitros, Sulfones, & Sulfoxides
Examples of EDG
Alkoxys, Syllyloxys, Aminos, Ester’s oxygen, Amide’s nitrogen, Alkyls
Diene Reactivity
** Want most stable s-cis conformation **
Diels-Alder Reaction Stereochemistry
Concerted mechanism = no changes in conformation
** Racemic mixtures because products are not chiral, so products must not have chirality **
Endo Transition State: EWG pointing in towards newly formed pi bond
** Stabilized by overlap between pi bond and p-orbital **
Exo Transition State: EWG pointing away from newly forming pi bond
Pyrrole
Resonance Energy = 22 Kcal/mol
Imidazole
Furan
RE = 16 Kcal/mol
Thiophene
RE = 29 Kcal/mol
Pyridine
RE = 22 Kcal/mol
Pyrimidine
Purine
Indole
Benzofuran
Quinoline
Benzene
RE = 36 Kcal/mol
Napthalene
RE = 60 Kcal/mol total, 30 Kcal/mol per ring
** Resonance energy per ring decreases as conjugation increases **
Anthracene
RE = 84 Kcal/mol total, 28 Kcal/mol per ring
Phenanthrene
RE = 91 Kcal/mol total, 30 Kcal/mol per ring
Phenol
Toluene
Xylene
Aniline
Benzoic Acid
Styrene
Anisole
Cresol
Aromatic Ring
Common Nomenclature
Name substituents with ortho (o), meta (m), para (p)
Aromatic Ring
IUPAC Nomenclature
Number the substituents with their position number
EAS
Electrophilic Aromatic Substitution
Aromatic Ring = Nucleophile
Carbocation = Electrophile
** Look for absence of leaving group and strong Nucleophile **
Chlorination
Reagents: Cl2 / AlCl3
Active Electrophile: Cl-Cl+ - AlCl3
Bromination
Reagents: Br2 / FeBr3
Active Electrophile: Br-Br+-FeBr3
Iodination
Reagents: 1/2 I2 / HNO3
Active Electrophile: I+
Nitration
Reagents: HNO3 / H2SO4
Active Electrophile: O=N+=O
Sulfonation
Reagents: SO3 / H2SO4
Active Electrophile: +SO4H
Desulfonation
Reagents: H30+ / H2O / Δ
Where do EDGs direct?
Ortho & Para
25x more reactive than benzene
Increases reaction rate
What’s different about Anisole compared to toluene?
Anisole is 1000x more reactive than benzene because it has a resonance structure with all octects filled (4 instead of 3 res. structures)
Where do EWGs direct?
Meta
** Avoids placing the carbocation next to the partial positive from the EWG **
Decelerates reaction rates
EDGs Directing Strength
(Most to Least)
- NH2
- OH
- OCH3
- NHCOCH3
Alkyl / -CH3
-H
Halides’s Directing Ability
Mildy Deactivating while Directing O/P
- F
- Cl
- Br
- I
EWGs Directing Strength
(Most to Least)
Strongly Deactivating and Directs Meta
- CHO
- CO2H
- OCCH3
- SO3H
- CN
- NO2
- +NR3
What is unique about halides as directing groups?
They are EDGs, but because they’re:
Inductively deactivating (less polar bond)
+ Resonancely mildly activating (poor p-orbital overlap)
= Mild Deactivating while directing to O/P
What is special about aniline and phenoxide?
Their by-products are more reactive than the original molecule, so they undergo overhalogenation and while substitube at all O/P positions
Aniline = needs buffer (NaHCO3)
Phenoxide = needs buffer (NaOH)
Kobe-Schmitt Reaction
Importance: Commercial production of aspirin
Reagents: 1) NaOH / CO2, 2) HCl
Extra step for aspirin: 3) CCOOOCC (turns OH into -OR)
** Need to already have a hydroxy (-OH) group / phenoxide **
Friedel-Craft Alkylation
Adds alkyl group to aromatic ring
Reagents: Carbocation + Aromatic Ring
Carbocation Formation from a Halide
Reagents: AgNO3 / Δ OR AlCl3
** Rearrangment can occur **
Carbocation Formation from Alcohol
Reagents: H2SO4 OR H3PO4 OR BF3
** Rearrangment can occur **
Carbocation Formation from Alkene
Reagents: H2SO4 OR H3PO4
** Rearrangment can occur **
3 Limitations of FC Alkylation
- No FC Alkylation on strongly deactivated rings (halides okay)
- Beware of carbocation rearrangment
- Potential for over alkylation w/EDGs
Acyl Group
-COR
Formyl Group
Fm
Acetyl group
Ac
Benzoyl Group
Bz
How to name acyl group (IUPAC)
Name R group on acyl group, then change the ending to -oyl
ex: butane -> butanoyl
Friedel-Craft Acylation
Adds acyl groups to aromatic rings
Reagents: Acid chloride/anhydride, AlCl3, + aromatic ring
Gatterman-Koch Formylation
Adds formyl group to aromatic ring
Reagents: CO / HCl / AlCl3 / CuCl
How does FC Acylation compare to Alkylation?
- No reaction on strongly deactivated rings
- No carbocation rearrangments
- No over acylation possible (acyl groups deactivate aromatic rings)
How do you do alkylation without the carbocation rearrangment?
Do an acylation, then use a clemmensen reduction to get rid of the C=O
Clemmensen Reducation Reagents: Zn(Hg) / HCL
NAS
Nucleophilic Aromatic Substitution
Two Mechanisms: Addition-Elimination & Benzyne
Addition-Elimination NAS Mechanism
Conditions: Leaving group on aromatic ring, EWG at the O and/or P positions
Reagents: Aromatic Ring (electrophile) + Nucleophile
X = F, Cl, Br, I, OTs
Benzyne NAS Mechanism
Conditions: Leaving group on aromatic ring with no EWG at O/P positions
Reagents: Aromatic ring w/EDG groups + Nucleophile
** Many products possible at each β-hydrogen can be attacked two ways **
Dissolving Metal Reduction
NH3 + Naº ⇔ NH3•e- + Na
Birch Reduction
Reagents: Na OR Li / NH3(l) / ROH
EWG: Sandwiched by the double bonds
EDG: In conjugation with double bonds
** Mechanism involving radicals **
Copper Coupling
Reagents: R’-X + R2CuLi
R’-X + R2CuLi → R’-R
Heck Reaction
Reagents: Pd+2 / PPh3 / TEA
“Who the heck peed twice in my tea”
Molecules: R-X + C=C-R’ → R-C=C-R’
Suzuki Reaction
Reagents: Pdº / NaOH
“Suzuki bike (B) with handlebars (OH2)
Williamson Ether Synthesis
Reagents: NaOEt
Oxidation
Reagents: warm, conc. Na2Cr2O7 / H2SO4
Turns everything but quatenary carbon centers on branches, esters, methoxys, and carboxylic acids into carboxylic acid branches
Oxidizing Phenol
Turns phenol into quinone
