39 Cards in this Set
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allyl
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a carbon atom adjacent to an alkene. also called an allylic structure.
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what's so special about the allyl
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allylic alkenes require less energy to break a bond than when breaking the bond of an alkane. For example, an alkane that couldn't undergo SN2 bc of weak nucleophiles and couldn't undergo SN1 bc of instability could do both if it was an allyl
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why are allyls so stable??
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resonance systems and delocalisation, not the same thing but result in the same thing
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nodes
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a place where there is zero probability of finding an electron
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bonding vs nonbonding vs antibonding
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bonding is the lowest energy system, delocalizes the entire system
anti bonding is neutral, it contributes the resonance structure and electron density
non bonding is the highest energy structure
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conjugation
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adjacent, parallel p-orbitals that allow electrons to move around
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allylic system
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only substitution, no elimination
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what is the most stable radical
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allylic radical
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allyls and substitution
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there is no E1 competition, the carbon is sp2 hybridized, there is no anti periplanar arrangement (required for E)
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NBS reagents
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specifically react w the allylic system, add bromine to the the allylic carbon. Works for other halogens too except for Fluorine
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diene
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two sets of double bonds`
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cummulated diene
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the double bonds are next to each other
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conjugated diene
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a single bond separates the double bonds, more stable than the isolated system. sigma bonds of this system more stable than sigma bonds of alkene bc of resonance, hybridization and short bonds
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isolated dienes
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an sp3 carbon separates the double bonds
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kinetic product
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forms faster when there are multiple forms of the product, product has a lower activation barrier or a more stable transition state, takes place at a lower temp (bc lower transition state)
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thermodynmic product
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has a mroe stable end product, irreversible at high temps
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Diels Alder
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new way to make carbon carbon bonds. Requires a diene (has 4pi electrons) and a dienophile (has 2pi electrons). Adds in cyclo addition. Thermodynamically this makes sense because you're breaking weaker pi bonds and making stronger sigma bonds. Diels Alder require an S-Cis conformation whi…
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endo rule
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concerted. Oxygen (the electronegative element) wants to be near electrons on the carbon. when Aldehyde is underneath the molecule, 6 carbons are above it/opposite it, less space.
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benzene rings
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jp orbital on every atom. Planar molecule, sp2, triganol planar. Total delocalization, more stable than a typical alkene
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how to be aromatic
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molecule must be full conjugated (completely delocalized, p orbital on every atom), must be cyclic, must be planar. All p orbitals need to be oriented to be able to overlap (parallel p orbitals on every atom), always 4n+2 pi electrons (huckel's rule)
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anti aromatic
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less stable than what aromatics should be, cyclic, fully conjugated, planar but DOES NOT follow Huckel's rule
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non-aromatic
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does not follow one of the other rules (cyclic, fully conjugate,d planar)
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pka and dienes
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the alkyl groups donate elecron density through hyperconjugation, pka's are much lower, hence more acidic
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electrophilic aromatic substitution
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benzene attacks electrophile and loses a double bond, gets a cation instead
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nitration
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first generate an electrophile, in this case it's O=N=O, which interacts w aromatics
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fuming sulfuric acid
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ONLY EAS REACTION THAT IS REVERSIBLE
react an aromatic ring with SO3/H2SO4. Reversed with H+/delta
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Friedel Grafts alkylation
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adds a carbon to an sp2 carbon
RX/AlX3, adds the R group to the carbon
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benzylic carbon
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carbon next to a benzene
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1. KMnO4/delta
2.H+
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makes everything (C=O)OH
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electrophile in EAS vs electrophile in friedl grafts
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EAS: interrupts aromaticity, attack of a nelectrophile. A/B rxn restores aromaticity
Friedl Graft: electrophile is a carbocation. Nearly impossible to use a 1o as a substrate
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friedl graft acylation
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benzene + R(C=O)Cl/ AlCl3, leads to (C=O)-R - called an acyl bonded to benzene
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two types of activators (ortho and para)
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inductively: electron density movement only through sigma bonds
resonance: any atom that has lone pair electrons that can be donated. is more powerful than inductive because you can draw all the resonance structures that show electron density
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two types of deactivators (meta)
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inductive: through the sigma bond
resonance: aldehyde, nitro group
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do aromatics undergo addition, substitution or both?
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only substitution, no addition because it would break the aromaticity (impossible)
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alkylation of enolates
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if limiting amounts of MeI are used, a poly alkylation occurs.
Doing an irreversible deprotonation means one final product and higher yield of said product
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roblems with enolate equlibration
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can react as a base and deprotonate the product
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aldols
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reactions are reversible
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non enolizable aldehyde
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an aldehyde with no alpha hydrogens (alpha hydrogens bond to alpha carbons- carbon bonded to functional group)
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amides
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amide bonds are quite stable, mroe stable than esters, acid chlorides and anhydrides but less stable than carboxylate anions
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CHEM 0320: Notes