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38 Cards in this Set
- Front
- Back
What is special about E2 reactions in cyclohexanes
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requires leaving groups be axial
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For each class of alkyl halide, list the factors in SN1 vs. E1
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Primary - cannot undergo
Secondary - Both Tertiary - Both but figure shows more SN1 (this is good since no SN2) |
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For each class of alkyl halide list the factors in SN2 vs. E2
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Primary - mostly substitution unless there is steric hindrance in the alkyl halide or base then elimination is favored
Secondary - both, the stronger and bulkier the base, the higher the temp, the more elimination Tertiary - only elimination |
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2 ether cleavage pathways
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ethers are cleaved by an SN1 (nucleophile goes with carbocation) pathway unless the instability of the carbocation requires SN2 (the nucleophile goes with less sterically hindered carbon)
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What does chromic acid (H2CrO4) do to primary etoh
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oxidize twice, first to aldehyde then to carboxylic acid
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2 types of halides that can undergo SN2 and SN1
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benzyllic and allylic
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2 types of halides that cannot undergo SN2 and SN1
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vinylic and arylic
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3 things that affect SN2
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leaving group - weaker base better leaving group
nucleophile - stronger base, better nuclophile solvent - aprotic favors more basic nucleophiles, protic favors less basic nucleophiles |
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2 polar protic solvents
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H2O, mtoh
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2 polar aprotic solvents
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DMSO, DMF
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In terms of stereochemistry, SN2 proceeds with complete _________ and SN1 proceeds with complete ______.
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inversion, racemization
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3 factors that affect SN2 vs SN1
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Nucleophile concentration, nucleophile reactivity, solvent
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How does polarity of the solvent affect SN1
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more polar means faster since the charged intermediate is stablized
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intermolecular vs. intramolecular, what two factors affect which reaction is dominant.
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High concentration of the molecule increases intermolecular and size of the ring formed (3 above 4, 5 and 6 above everything else)
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3 exceptions to zaitzev's rule
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bulky bases that cannot reach the more substituted beta carbon
conjugated alkenes fluorine leaving groups - transition state is more like a carbanion which is more stable as primary |
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2 factors in E2 vs E1
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primary alkylhalides can only undergo E2
with sec and tert, E2 is favored with high conc. of strong base in aprotic polar solvent |
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4 factors affecting SN2/E2 competition
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steric hindrance of a.h. or base favors elimination
strong base favors elimination high temp favors elimination tert-alkylhalide favors elimination |
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important thing to remember in williamson ether synthesis
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less hindered group should be provided by the alkyl halide
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How do alcohols react
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Sec and tert by SN1, primary by SN2
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What does HCl require to react with etoh
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ZnCl2
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2 addtional methods for converting etoh to a.h.
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phosphorous tribromide(or chloride), thonyl chloride
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alternatives to a.h. for leaving groups from etoh
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sulfontate ester, tosylate
TsCl in pyradine |
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how are alcohols dehydrated
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with phosporic or sulfuric acid
sec. tert by E1, primary by E2 |
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dehydration under milder conditions
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POCl3 (phosphorous oxychloride) pyridine, 0 degrees
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how do you make ketones from alcohol
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you need a secondary alcohol and chromic acid
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how do you make carboxylic acid from alcohol
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primary alcohol oxidized twice by chromic acid
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how do you make an aldehyde from alcohol
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single oxidation of a primary alcohol by PCC/CH2Cl2
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what happens when you oxidize tertiary alcohols
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nothing there is no hydrogen to take
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describe how ethers react with hydrogen halides
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By SN1 when a secondary or tertiary carbocation can form. Otherwise by SN2 where the nucleophile attacks the less sterically hindered carbon
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how are griniard reagents made
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Mg/diethylether or THF
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Two components of a diels alder reaction.
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diene and dienophile
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draw the following: bromobenzene, chlorobenzene, nitrobenzene, ethylbenzene, toluene, phenol, aniline, benzenesulfonic acid, anisole, styrene, benzaldehyde, benzoic acid, benzonitrile, isopropylbenzene, sec-butylbenzene, tert-butylbenzene, 2-phenylbenzene, 3-phenylbenzene
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last page of Lec. 20
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describe what is needed for halogenation of benzene
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Br2/FeBr3 (or Cl), lewis acid catalyst, the Fe pulls on the Br2 while the benzene attacks the Br
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describe what is needed for nitration of benzene (nitrobenzene)
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H2SO4 generates nitronium ion (NO2+) from nitric acid (HNO3) by adding a proton and water falls off
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describe what is needed for the sulfoniation of benzene (benzenesulfonic acid)
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H2SO4 and heat, one of the sulfuric acids adds a proton to the other and a water falls off leaving a sulfonium that is open to attack
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describe what is used in friedel crafts acylation
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a benzene with an acyl chloride and AlCl3/H20, this pops off the chloride the positively charged acylium ion then is open to attack by electrophilic aromatic substitution
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describe what is used in a friedel crafts alkylation
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benzene and 1-chlorobutane with AlCl3 at zero degrees, this pops off the chlorine and makes a primary carbocation which is open to attach by electrophilic aromatic substitution
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How can you insert a bromine at the benzylic position of an alkylbenzene
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with NBS heat and peroxide
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