Organic chemistry Lab pratical - Sheet1.csv

"Is to determine the purity of a compound

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).

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.

"When a nonpolar solvent is passed through the absorbent

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.

"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

"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)

The mechanism of an Sn2 reaction involves a one-step biomolecular displacement of the leaving group by a nucelophile with an inversion of configeration

The mechanism of an Sn1 reaction involves intial formation of a carbocation (rate determining step) followed by rapid reaction with the nucelophile

1. Formation of a carbocation (most important) 2. Leaving group. 3. Polarity of the solvent 4. Nucleophile

1. Steric factors (most important). 2. Nucelophile 3. Solvent polarity 4. Leaving group

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

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.

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]

Sn1 reactions show complete to partial racemization of sterochemistry. Where Sn2 reactions show inversion of the configuration

"methy<1 aklyl < 2 alkyl

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.

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.

"Polar aprotic solvents. DMSO

"Polar protic solvents. H2O

All nucleophiles are Bronsted bases (proton acceptor/donating electrons). Sterically unhindered strong bases are good nucleophiles. With a pKa of greater than 11.

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.

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.

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.

"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

"Was given an unknown alcohol and had to figure out what it was using a number of tests. Chromic acid test. Lucas 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.

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!!!

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.

An R group attached to a a CH with an OH and CH3 bound to it. Secondary alcohol.

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.