Term
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Definition
Species with an unpaired electron group
ex) OH- CH3O I
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Term
| Leaving Group and Order from strongest to weakest |
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Definition
substituent that can leave as a relatively stable, weakly basic molecule
I>Br>Cl>F |
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Term
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Definition
Can only occur with
methyl, primary, or a secondary carbon
needs a strong nucleophile
works better in a polar aprotic solvent
needs a good leaving group |
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Term
| Polar aprotic solvent versus a Polar protic solven |
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Definition
Polar Protic
has the ability to solvate cations and anions
mainly occurs with SN1 reactions because the substituent is a carbocation
examples: water, alcohol
Polar Aprotic
does not have a electronegative element attached to a hydrogen
mainly occurs with SN2 because |
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Term
| aprotic solvent vs protic solvent in substitution reactions |
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Definition
in protic solvent hydrogen bonding with the nucleophile occurs and hinders the reactivity
Hydrogen bonds to a smaller nucleophilic atom are the strongest
Hence a flouride anion is strongly solvated and has the most concentrated charge
On the other hand a Iodide anion is weakly solvated in a polar protic solvent
Stongest nucleophile in a protic solvent I>Br>Cl>F |
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Term
| Polar protic solvent important fact |
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Definition
note the larger the atom of the molecule attached to the hydrogen the stronger the nucleophile
example
R-SH is a stronger nucleophile than R-OH because suflur is a bigger atom than hydrogen |
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Term
| Relative nucleophilicilcity in PROTIC solvents |
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Definition
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Term
Aprotic solvents and SN2 reactions
examples of good solvents and why they are good |
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Definition
DMF, DMSO, DMA, HMPA
they dissolve ionic compounds and solvate cations very well
NOTE aprotics solvents do not solvate anions to an appreciable extent
Aprotic solvent trends for halide nucleophilicity strongest to weakest
F>Cl>Br>I |
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Term
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Definition
can only occur with a tertiary halide
requires a weak nucleophile
mostly happens in a polar protic solvent
requires a good leaving group |
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Term
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Definition
must have a tertiary halide
wants a poor nucleophile
favored at high temperatures
needs a good leaving group |
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Term
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Definition
can occur with primary, secondary, or tertiary halides
good leaving group
higher temperatures
NOT FINISHED |
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Term
| Behaviors of and atom or molecule |
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Definition
bronstead acid donates a proton
bronstead base accepts an electron
poor leaving group will not allow for a reaction
sterically hindered electrophiles require more free energy |
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Term
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Definition
| trivalent carbon with a positive formal charge |
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Term
| stablility of carbocations |
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Definition
most to least
3>2>1>methyl |
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Term
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Definition
electron delocalization from a filled bonding orbital to an adjacent unfilled orbital
anytime a charged can be dispersed or delocalized a system will be stable
hyperconjugation will occur
greatest to least 3>2>1
methyl does not allow for hyperconjugation |
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Term
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Definition
exergonic - downhill or negative free energy
1) Nu + R-L
2)Nu-R----L
3) Nu-R + L
endergonic - uphill or positive free energy
1) Nu +R-L
2)Nu-R----L
3) Nu-R + L
Look at graphs!
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Term
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Definition
SN1 - causes racemization - randomizes - transforms optically active compound in to a racemic form
- causes chiral to become achiral
SN2 - causes inversion |
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Term
| Substitution Vs Elimination |
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Definition
Primary halide + unhindered base = substitution
Secondary halide + strong base = elimination
NOTE: anytime the SUBSTRATE is sterically hindered elimination is favored
Tertiary halide + stron base= elimination
NOTE - the only substitution reaction that could occur would be SN1 |
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Term
| Tempurature and reactions |
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Definition
Yes higher tempuratures do favor elimination but substitution can still occur... tempurature is probly not the best indicator in my opinion
IMPORTANT
even with high tempurature substitution can occur unless you have a strong base and a tertiary halide |
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Term
| polarizability and basicity and how they are related |
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Definition
| strong bases are slightly polarizable |
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Term
| Basicity and polarizablitiy in predicting reactions |
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Definition
use of a strong base increases chance of elimination
example - NH2
Use of a weak base favors substutution
example - Cl, CH3CO2, BR, I , RS |
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Term
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Definition
weak base = both SN1 and E1
strong base + tertiary = E2 but if it has a low tempurate you will get a small amount of SN1 |
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Term
| Bimolecular vs Unimolecular |
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Definition
bi - 2 species involved SN2
uni - 1 specie involved SN1 |
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Term
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Definition
the bigger the halogen the weaker the bond strength
halogens pop off easily and allow for the possibilty of a multiple bond |
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Term
| phenyl halide and a vinyl halide |
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Definition
phenyl - halogen attached to a benzene ring
vinyl - halogen that is attached to a carbon thats a attached to another carbon by a double bond |
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Term
| alkyl halide is ALWAYS the... |
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Definition
| substrate and therefore is always the molecule containing the leaving group |
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Term
| Hughes Ingnold mechanismSN2 |
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Definition
the nucleophile approaches the carbon bearing leaving group from the back
bond between nucleophile and carbon strengthens
leaving group bond weakens and floats off |
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Term
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Definition
| the rate determining step - slow step |
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Term
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Definition
| an SN1 reaction of an alkylhalide with water |
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Term
| reactions of an SN1 pathway |
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Definition
| the only reactions that happen at a reasonable rate are the ones that form tertiary halides |
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Term
| reactivity rate depends on the |
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Definition
strength of the nucleophile
strong = fast
weak = slow |
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Term
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Definition
| SN2 allows us to convert one functional group to another |
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Term
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Definition
| the larger molecule is the stronger nucleophile |
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Term
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Definition
| the rate of the reaction depends of the concentration of the substrate and nucleophile in _________ reactions |
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Term
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Definition
| do NOT rely on molar concentrations of the nucleophile |
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