Organic chemistry Lab pratical - Sheet1.csv

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Organic chemistry Lab pratical - Sheet1.csv
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2012-03-13 11:14:59
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Organic Chem Practical
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Chem 3302 lab practical
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  1. Thin layer chromatography (TLC)
    "Is to determine the purity of a compound
  2. TLC separation is used on what types of liquids
    Is the separation of moderately volatile or nonvolatile substances based upon differnential adsorption on an inert solid (staionary phase). immersed in an organic solvent or solvent mixture (mobile phase).
  3. Mechanism of TLC
    Compounds are separated by adsorption chromatography based upon differential attachment of molecules to the adsorbent and the polarity of the solvent used for the separation. POLAR COMPOUNDS are strongly attracted and held by a polar adsorbent. NONPOLAR are held weakly.
  4. Selecting solvents for TLC
    "When a nonpolar solvent is passed through the absorbent
  5. Calculating Rf values TLC
    The distance traveled (middle of the spot)/total distance of solvent traveled. In general the Rf value on silica gel or alumina are decreased by decreasing the polarity of the solvent and increaseing the solvent polarity. This is used if a single solvent fails to give adequate separation a solvent mixture is used.
  6. Column Chromatography
    "Works like TLC except that solvents are passd down through the adsorbent holding the mixture to be separated (descending chromatography). Column chromatography can be used as a preparative verision of TLC that allows for the SEPARATION AND ISOLATION OF PRODUCTS BY COLLECTION OF ELUTED FRACTIONS. The major difference is that the sample is loaded at the top of an adsorbent
  7. Gravity column chromatography
    "In lab we used this method in conjuction with ""flash chromatography"" which used a low pressure vacume to assist the movement of the solvent down the column. The setup is a a column tube filled with an adsorbent (silica gel)
  8. Sn2 Reation of Alkyl Halides
    The mechanism of an Sn2 reaction involves a one-step biomolecular displacement of the leaving group by a nucelophile with an inversion of configeration
  9. Sn1 Reactions of Alkyl Halides
    The mechanism of an Sn1 reaction involves intial formation of a carbocation (rate determining step) followed by rapid reaction with the nucelophile
  10. Rate of reaction of an Sn1 reaction is determined by
    1. Formation of a carbocation (most important) 2. Leaving group. 3. Polarity of the solvent 4. Nucleophile
  11. Rate of reaction of an Sn2 reaction is determined by
    1. Steric factors (most important). 2. Nucelophile 3. Solvent polarity 4. Leaving group
  12. Ferrocene vs Acetylferrocene
    Ferrocene is two benzene rings held together by a an Fe (iron). Making it nonpolar. The acetylferrocene is the same structure but on one of the benzene rings it has an acetly group coming off it. This acetyl group makes this molecule more polar and will come out second during a column chromatography
  13. Rate of Sn1 Reaction
    Since this is a first order reaction based on the formation of a carbocation. The rate has NO dependence on the nucleophile. Any Sn1 substitution reaction rate depends only upon [R-Lv] proceeeds via an Sn1 mechanism.
  14. Rate of Sn2 Reaction
    Since Sn2 is a single step (bimolecular) doubling the concentration of either the nucleophile or the [R-lv] will double the speed. If you double both the rate of reaction will increase 4 times. Formula = Rate = k[R-Lv][Nucleophile]
  15. Sterochemistry of Sn1 vs. Sn2
    Sn1 reactions show complete to partial racemization of sterochemistry. Where Sn2 reactions show inversion of the configuration
  16. Stability of carbocations
    "methy<1 aklyl < 2 alkyl
  17. Steric hinderance of Sn2
    Ch3X (methyl) > RCH2X (Primary) > Secondary R2-ChX. Tertiary will never occur becasue of the blocking to make the rearside attack. You also must condiser the beta branching and its effect on Sn2 and can lead to E2.
  18. Leaving groups
    The leaving group developes a partial negative charge in both Sn1 and Sn2 reactions. The MOST STABLE ANION are the best leaving groups. The weak conjugate bases of strong acids. A good leaving group if a H is added to it will be a strong acid.
  19. Sn2 solvents
    "Polar aprotic solvents. DMSO
  20. Sn1 solvents
    "Polar protic solvents. H2O
  21. Good Nucleophiles
    All nucleophiles are Bronsted bases (proton acceptor/donating electrons). Sterically unhindered strong bases are good nucleophiles. With a pKa of greater than 11.
  22. Synthesis of an Alkyl Halide from an Alcohol
    Tertiary alcohols can be easily converted to alkyl chlorides by the addition of concentrated hydrochloric acid to the alcohol. The mechanism involved is the tertitary OH will bind with the Free H+ to form H2O (an excellent leaving group). Water will remove itself to make a stable carbocation. Now Cl- will bind here makeing a alkyl halide.
  23. Use of bicarb in Synthesis of an Alkyl Halide
    The bicarb is used to convert the excess HCl in the organic layer to CO2 and H2O + NaCl. Sodium Hydroxide could be used instead (NaOH) but will can lead to a side reaction in which the NaOH will deprotinate one of the carbons and lead to an E1 reaction.
  24. Mechanism for the Macroscale Synthesis of Butyl Acetate
    Acid catalyzed intermolecular dehydration of a primary alcohol. Involves the addtion of Hydrogen to the primary alcohol (making H2O a good leaving group). Then the nucleophile (acetic acid) is added and does a Sn2 reaction bumping off the H2O to form an ether with an extra hydrogen which is then given back to the acid.
  25. Macroscale synthesis of butyl acetate experiment summary
    "Used a primary alcohol (1-butanol) then added acetic acid and an acid catalist (sulfuric acid). This did an acid catalyist dehydration to create an ether
  26. Alcohol Unknown experiment summary
    "Was given an unknown alcohol and had to figure out what it was using a number of tests. Chromic acid test. Lucas Test
  27. Chromic Acid Test
    Add 1 drop of chromic acid solution. Observe carefully for a blue-green precipitate to form indicating a postive reaction. This indicates a primary or secondary alcohol. TERTIRARY ALCOHOLS DO NOT REACT.
  28. Lucas Test
    Add about 10 drops of lucas reagent. Swirl rapidly and look for the formation of cloudiness or a separation of two layers. This is conducting a Sn1 reaction. The length of time can vary on the type of alcohol. USED TO TEST FOR TERTIARY OR SECONDARY ALCOHOLS. Primary alcohols should not react!!!
  29. Iodoform Test
    Add 1 ml of water and 1 ml of 10% aqueous sodium hdroxide and 1.5 mL of .5 M iodine-potassium iodide solution. A positive result is the disappearance of the brown color (iodine) and the formation of a yellow precipitate (iodoform). You can filter the precipitate if wanted to and take the mp should be around 118-119. POSITIVE WIL SHOW 2-ALKANOLS R-CH-OH-CH3.
  30. Alkanols
    An R group attached to a a CH with an OH and CH3 bound to it. Secondary alcohol.
  31. 3.5 Dinitrobenzoate derivative
    Can bind an unknown alcohol with 3.5 dinitrobenzoyl chloride to make a derivative and take its mp to help identify it. Add 200 mg of 3.5 dinitrobenzoyl chloride to about 100mg of unknown alcohol. Gently head and stir solution until boiling. Allow to cool then add .3 of distilled water then cool in ice bath. Filter through Hirsh funnel. Wash with 10% sodium carbonate to dissolve the impurities then was again with a small portion of distilled water and let air dry. The now solid product can be recryalized from a ethanol-water solvent pair. Dissolve the filter and recyrstallize and take mp.

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