MCAT Organic Chemistry Quickies 1

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mightyred230
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MCAT Organic Chemistry Quickies 1
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2011-05-09 23:02:16
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  1. Can you "resonate" onto a sp3 hybrydized atom?
    No
  2. What is the hybridization of a radical carbon?
    sp2
  3. What is radical inhibition?
    When the free radical is inihibited by molecular oxygen. This forms a less reactive alkyl peroxy radical.
  4. Which enantiomer is the primary product of halogenation?
    Both leading to a racemic mixture (if unsymmetrical). The halogen can attack from bottom or top of the sp2 hybdrized carbon.
  5. Radical and carbocation stability
    methyl < 1 < 2 < 3
  6. Is bromination or chlorination more selective?
    • Bromination - favors tertiary
    • Chlorination - less selective because its greatly exothermic
  7. Better nucleophile trend
    • Negative charge on the least electronegative atom (C- > N- > O- > X-)
    • Carbon is greatest nucleophile because it is not electronegative enough to hold the extra pair of electrons (-) as oxygen can so it is a highly reactive nucleophile
  8. Remember the possibility of hydride and methyl shifts!
  9. What are nucleophiles?
    • Nucleophiles - have unshared pairs of electrons, partial negative, electron pair donors, lewis base/ligand
    • N strength increases as negative charge increases
    • N strength increases going down the period (F<Cl<Br<I)
    • N strength increases going left in the period (OH < NH < C)
    • basically, the less electronegative and more negative the charge, the stronger the nucleophile
  10. Electrophiles are lewis acids or bases?
    Acids
  11. SN2 mechanism characteristics
    • reactivity: CH3 > 1 > 2 >3
    • stereochem: Inversion of stereochemistr due to backside attack
    • kinetics: rate = k [nucleophile][electrophile] - second order
    • solvent: polar aprotic
    • rearrangement: no rearrangements b/c no carbocation formatoin
    • favored conditions: strong, non-bulky nucleophile
  12. SN1 mechanism characteristics
    • reactivity: 3 > 2 > 1 > methyhl
    • sterochem: racemate
    • kinetics: rate: k[electrophile] - carbocation formation
    • solvent: polar protic - stabilize carbocation
    • rerrangements: possible to make more stable carbocation
    • favored conditions: non-basic, weak nucleophiles
  13. Can ethers form intermolecular H bonds?
    No, becuase it does not have H attached to NOF atoms, but it can H bond with water and other atoms with H
  14. In an amide bond, what is the hybdrizatoin of the N group?
    sp2 because it can participate in resonance with the adjacent carbonyl group
  15. E1 mechanism
    • formation of carbocation b/c leaving group leaves first
    • need beta hydrogens. if no adjacent hydrogens are available, eliminaiton cannot occur
    • reactivity: 3 > 2 >>>> 1
    • stereochemistry: most substituted favored. trans over cis
    • kinetics: rate: k[haloalkane]
    • solvent: protic
    • rearrangemenst: possible!
    • favoring conditions: weak base and high temp
  16. E2 mechanism
    • stereochem: anticoplanar or trans diaxial
    • reactivity: 3 > 2 > 1
    • reactoin rate: k[base][substrate]
    • solvent: polar aprotic
    • arrangements: nope
    • favoring conditions: strong bulky bases, high temp
  17. The stronger the acid....
    • The more stable the conjugate bas
    • electron withdrawing groups and the ability to resonate stabilize the conjugate base
    • electron donating groups would destabilize = stronger base, weak acid
  18. Electrophilic Additions
    • usually with pi bonds
    • beaware of enantiomer formations and other stereochem such as hindrance
    • markovnikov and anti
  19. 3 alkane + H2SO4/H2O
    forms an alcohol
  20. Reactoins that result in antimarkovnikov
    • hydroboration (1. BH3/B2H6, 2. H2O2)
    • HBr addition with peroxides
  21. Oxidation of pi bonds with Dilute KMnO4
    Syn addition of diol
  22. Hydrogenation reactions:
    • 1) H2 with Ni, Pd, Pt = syn addition of H2
    • 2) Alyne + lindlar catalyst with Pd = syn addition of H-H across pi bond resulting in cis - stops hydrogenation reduction of alkyne at alkene stage
    • 3) Na, NH3 + alykne = trans alkene. does not reduce alkenes
  23. Ozonolysis
    Double bond to carbonyl gruop (ketone or aldehyde possible)
  24. Huckel rule
    • 4n+2 = number of pi electrons
    • n = whole number
  25. O,P directors
    • Ring activators
    • Donate a pair of electrons
    • R groups
    • Halogens are O,P but deactivating
  26. Meta Directors
    • Deactivators
    • - NR3, N02, CN
    • - things that pull electrons
  27. Which is more stable keto or enol
    keto
  28. Oxdizing agents
    • need a hydrogen to remove. so if you have a tertiary alcohol, you cannot oxidize it
    • some oxidizing agents include chromates, conc nitritic acid, oxygen
  29. Aldol condensation
    • requires alpha hydrogens
    • results in alpha beta unsaturated ketone where the C=C bond is between the alpha and beta carbons
    • the c=c is more electrophilic, so nucleophiles will attack c=c first then resonate to form enol which can tautoremize to a more stable keto form - this is called michael addition
  30. grignard
    carbonyl to alcohol even with good leaving group
  31. Michael addition (post aldol condensation)
    • remember, the oxygen and double bond can undergo keto-enol tauto (keto is favored)
  32. Thermodynamic vs kinetic product
    thermodyanamic is most stable
  33. What type of carboxylic acids are prone to decarboxylations?
    Those that have carbonyl groups beta to the carboxylate
  34. Carboxylic acid + alcohol =?
    Ester
  35. Extractions seperate based on:
    • Solubility
    • ions tend to dissolve in the aq layer. As a result, you use acid bases
    • NaOH would deprotenate a weak acid
    • HCO3 would deprotenate a strong acid
    • This allows one to separate a strong acid from strong base
  36. In TLC, is the plate polar or nonpolar?
    Polar - allows nonpolar materials to travel up further while polar substancs would stick to the plate
  37. Fractional vs simple distillation?
    Fractional allows for the separation of substances with similar boiling poitns
  38. UV spec?
    Conjugated systems
  39. How many Ka's does an amino acid have?
    2 COOH and NH3 groups
  40. Isolectric point. Define.
    The point where the amino acid acts as a zwitterion which has a net neutral charge. The pI is also the equivalence point.
  41. What does benedicts solution detect?
    • Detects carbonyl units of sugars
    • Hemiacetals = positive test (plain glucose)
    • Glycogen = weakly positive (only the end points are hemiacetals)
    • Benedicts solution is an oxidized form of copper - this gets reduced by the sugars (Cu2+ to Cu+) - this oxidizes the sugar in return.
    • The anomeric carbon in glucose gets oxidized.
  42. What are the two anomers of glucose?
    • Alpha - OH pointing down
    • Beta - OH pointing up
    • Mutorotation = conversion b/w both (has to go through the chain formula)
  43. what type of bonds are between nucleic acids
    phosphodiester
  44. gem vs vic
    • gem - 2 X or 2 OH on same carbon
    • vic - 2 X or 2 OH on adjacent carbons (nipple piercings

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