Ochem 343, Part 2 Flashcards
(42 cards)
SN2 considerations
- sterics
- strength of nucleophile
- solvent influence
Le Chateliers Principle
When a change disrupts an equilibrium, the system adjusts to diminish the change
Zaitser’s Rule
in beta elimination reactions, more substituted alkene usually forms preferentially in E1 and E2.
acidity of H on sp3 vs. sp2 vs. sp C, role in alkyne synthesis via E2
The H on an sp2 hybridized C is MORE acidic (more reactive) than the H on an sp3 c.
H on an sp C is the MOST acidic and very reactive. (more S character = lower in energy).
In Alkyne synthesis via E2 reactions, this is important because you need more than 1 equivalent of strong base to keep reaction moving toward desired products.
Geminal dihalide
A geminal dihalide is 2 halides (X atoms) on the same C
Vicinal dihalide
A vicinal dihalide has 2 halides (X atoms) on adjacent carbons from each other
peroxide
Peroxides are a group of compounds with the structure R−O−O−R.
Initiation def and methods
=Making radicals
Can use peroxides (R-O-O-R)
hv light
What is so favorable about anti-coplanar in E2?
- obitals aligned and pi bonds starting to form, so C on its way to sp2
- favorable orbital arrangement; hyperconjucation happening above and below the plane
- charge; partial charges generally favorable in anticoplanar arrangements
- Low energy conformation trans state is where these groups are stable and spending most of their time.
Why do E2 reactions tend to follow Zaitsev’s Rule?
E2 follows Zaitsev’s because there are typically more anti-coplanar Hydrogens in more branched, or non-terminal, positions.
Why do E1 reactions tend to follow Zaitsev’s Rule?
E1 follows Zaitsev’s because the relative stability of the carbo cation intermediate determines the products, and the more stable carbo cation will be the one on the more substituted position.
Can H-S bonds drive an E2?
No! H-S bonds are much more acidic than O-H
= weaker, more stable base. E2 not possible.
Grignard Reagent
“grin-yard”
Insertion of Mg into a C-halogen bond
Organolithium Reagent
Li in 2 eq. bonds with X (either Cl or Br) and precipitates as a solid salt. The second eq. takes the place of the Cl or Br on the substrate.
Carbene
Carbon nucleophiles.
Can also accept electrons via empty p orbital.
Carbon with 2 attachments and a lone pair.
Approximately sp2 hybridized.
Divalent (no charge).
Highly reactive.
def of carbonion
lone pair on carbon with a negative charge
3 things that carbo cations do:
Carbo cations:
1. act as acids (essentially protonated alkenes).
2. attach nucleophiles.
3. Rearrange.
Like all strong acids, they are INCOMPATIBLE with strong bases.
Grignard reagent
A compound of the form R-Mg-X,
Where X is Br, Cl, or I.
Prepared in ETHER solvent (R-O-R), then ether boiled off.
In reactions, the C is more electronegative than the metal, so C has the partial negative charge.
Reacts as a carbanion, a strong base.
Won’t work with solvent or any H (even H in water is too acidic).
Organolithium reagents
Compounds of the form R-Li.
Prepared in oxygen-free in hydrocarbons.
In reactions, the C is more electronegative than the metal, so C has the partial negative charge.
Reacts as a carbanion, a strong base.
Carbanion
A carbon with 3 bonds and a lone pair, giving it a formal negative charge.
Carbene
A species with a divalent carbon atom—a highly reactive carbon, neutral, with just 2 bonds plus a lone pair.
Can act as an electrophile via empty p orbital, or as a nucleophile via lone electron pair in sp2 orbital (singlet carbene).
When you see metal on C…
Carbon will generally behave as though it has a lone pair in place of that covalent bond.
Tautanimers
Isomers that differ in location of api system and where an H atom is attached.
Alkyl substituent
A carbon chain minus a H.
Alkylating agent adds an alkyl chain.
