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23 Cards in this Set
- Front
- Back
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Primary alcohol + Water |
Sn2 reaction requires heat protonation of -OH group backside nu attack and LG leaves (HOH) inversion of stereochemistry |
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secondary alcohol + water |
Sn1 reaction requires heat protonation of -OH group LG leaves to form carbocation rearrangement may occur nu attack (top or bottom)
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tertiary alcohol + water |
Sn1 reaction doesnt require heat protonation of -OH group LG leaves to form carbocation rearrangement may occur nu attack (top or bottom) possible competing E1 reaction could then undergo substitution and form substitution product
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sulfonate ester synthesis |
sulfonyl chloride + alcohol in pyrridine (acts as a solvent and base) ex: TsCl --> OTs
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What is the function of ZnCl in halogenation of alcohols? |
is a better activating agent when alcohol reacts with Cl - the weakest nucleophile helps speed the reaction AND shift equilibrium (make the reaction go to completion by forming more of the alkyl halide) |
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What is the function of Pyrridine? |
halogenation reactions with PBr3/PCl3/SOCl2 synthesis of sulfonate esters acts as a solvent and a base |
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how is a sulfonate ester synthesized? |
from sulfonyl chloride and alcohol Sn2 reaction pyrridine solvent |
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why sulfonate esters are useful in synthesis |
anion makes a good LG (stabilized by delocalized electrons) ex: -OTs |
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difference between dehydration with POCl3 (mild) and with H2SO4 (reactive) |
mild conditions = E2 reaction reactive conditions = E1 reaction formation of carbocation intermediate may or may not change products formed |
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oxidation with secondary vs primary alcohols (tertiary cannot be oxidized) |
secondary --> ketones primary --> aldehydes |
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oxidation (primary alcohol) with H2CrO4 (strong oxidizing agent) vs PCC/CH2Cl2 or HOCl (weak) |
strong --> further oxidation leads to carboxylic acid formation weak --> only forms an aldehyde |
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R-O-R + HX R-O-H + HX |
O is protonated LG (HOR or HOH) leaves depending on stability of the carbocation formed, the rxn is Sn2 or Sn1 |
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why can't ethers be activated by methods other than protonation? |
because the LG would not contain a proton alcohols already have a proton available, so they can be activated by other methods |
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synthesizing an epoxide (2 methods) |
alkene + peroxyacid or alkene + halogen (Cl2), then addition of reducing agent (LiAlH4) then intramolecular Sn2 reaction |
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in ACIDIC conditions, where does the nucleophile attack the epoxide? |
at the more substituted carbon because the protonated -OH group will form an intermediate favoring the more stable carbocation (more substituted) |
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in BASIC conditions, where does the nucleophile attack the epoxide? |
at the less substituted carbon because the O is not protonated, so it does not form a carbocation intermediate therefore, the nucleophile will come in at the less sterically hindered site |
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when would you want to use an epoxide in synthesis? |
using a sterically hindered epoxide in basic conditions would cause nu attack at the less substituted carbon and alcohol formation at more substituted carbon using an epoxide in acidic conditions would cause less substituted alcohol to form and nucleophilic attack at the more substituted position adding water to an epoxide avoids carbocation rearrangement: addition of hydride reducing agent THEN the addition of acid to protonate. (if conditions were acidic a rearrangement would occur) |
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how would you form a trans-1,2-diol vs a cis-1,2-diol? |
trans --> use epoxide and acid cis --> use OsO4 (structure causes it to add both oxygens at the same side) then add H2O2 and H20 to hydrolize (OsO4 is a product) |
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what is the purpose of crown ethers? |
they hold metal cations with electrons from oxygen in a ring and make a nucleophile more reactive |
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what does cytochrome P450 do? |
it is a powerful oxidizing reagent that can interrupt aromaticity and form epoxides |
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the hofman elimination reaction |
form the anti-zaitsev product base removes H from carbon that is least substituted transition state is more stable when partial negative charge is C closest to N (N has a partial positive charge) |
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the reaction of mustard structures |
intramolecular reactions form 3-membered rings that are very reactive water adds to ring to form alcohol |
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why use thiolate ion instead of alkoxide ion? |
thiolate ions are better nucleophiles forms the sulfur analog of an ether |
