o chem midterm

what is chromatography?

Chromatography is a separation technique based on the distribution or partitioning of a mixture of compounds between a stationary phase and a mobile (moving) phase. The compounds in the mixture should exhibit different solubilities in the two phases for separation to take place. There are several types of chromatography:

Jones Oxidation -what are the reagents?

CrO3/H2SO4

what reagents are used int he ferric chloride test

FeCl3

stable enols -what test do you use for this?

Ferric chloride test

what do we use if we are extracting a base, for instance amines?

HCl (aq)

what reagents does the Lucas test use

HCl/ZnCl2

stereochemistry

The mode of addition of bromine to an alkene is anti.

-what happens to acidity as pKa drops?

Acidity increases

what are the reagents used for the SN1 test?

AgNO3/ethanol

more product practice

**didnt finish top two on the right

positive test -A positive test is the appearance of a ______ or _______ due to the formation of NaCl which is insoluble in the acetone. -A false positive test is possible if NaI is not soluble in the alkyl halide and the NaI precipitates out. This can be prevented by adding more acetone. -A false negative test is possible if water is present because NaCl is soluble in water.

- precipitate -turbidity

-inductive effect

-Acidity: CH3CO2H > CH3CH2OH > CH3CH2NH2 > CH3CH2CH3

SN2

-An SN2 reaction is a bimolecular nucleophilic substitution that occurs in one step. In this reaction an alkyl chloride is converted into an alkyl iodide. -1 step. leaving group and incoming group come in same step -wherever previous substituent was, new group comes in on opposite side

-Why are tertiary carbocations more stable then secondary and secondary more stable than primary? -Why are benzylic and allylic carbocations stable enough to undergo SN1 reactions?

-Tertiary carbocations are stabilized by the presence of nearby alkyl groups. Alkyl groups are electron pushes and donate electron-density to help stabilize the positive charge. -Resonance stabilized carbocations (practice drawing the resonance structures).

-what happens to the acidity as size increases? -What is the inductive effect? -what things come into play when thinking about acidity?

-acidity increases -shifting of electrons in a bond as a result of the electronegativity of nearby atoms. More electronegative atoms have greater inductive effect so are stronger acids -electronegativity, size, and inductive effect

The acidity of halocarboxylic acids increases with the _________ and decreases with the_________ to the carboxylic acid group.

-electronegativity of the halogen (kind and number) - distance of the halogen FCH2CO2H > ClCH2CO2H Cl2CHCO2H > ClCH2CO2H 2-bromobutanoic acid > 3-bromobutanoic acid > 4-bromobutanoic acid

pic of stability of alkenes and carbocation stability

-major product = trans product -Vic has more on this stuff on hers

stability of alkenes:

-the more substituted the alkene the more stable -trans more stable than cis

Bromine test for unsaturation -Alkenes contain a carbon-carbon double bond that is electron rich and undergoes electrophilic addition. A check for the presence of a carbon-carbon double bond can be done quickly using bromine in dichloromethane (Br2/CH2Cl2). The bromine solution is a red-brown color and when added to an alkene turns colorless, which indicates a positive test. This reaction, including stereochemistry, will be discussed further in the upcoming qualitative analysis experiment. An example reaction is: pic!

-this test is essentially testing for presence of alkene -saturation/unsaturation has to do with hydrogens. Saturated means there are H's on all. Unsaturated have double bond/s, triple bond, or ring bc you have to lose the max number of H's to form this

positive test -The 2,4-DNP solution is red and a positive test is indicated by what?

A yellow-orange or red precipitate. A false positive test can occur if the 2,4-DNP precipitates out of solution. Extended conjugation will shift the color towards red.

Bromination Br2/CH2Cl2

Alkenes, olefins, contain a carbon-carbon double bond that is electron rich. Alkenes readily undergo electrophilic addition at the double bond.

what are the reagents for bromination?

Br2/CH2Cl2

alkenes -what test is used for these?

Bromination

SN1 AgNO3/ethanol

In SN1 reactions the rate-determining step is the formation of the carbocation. Therefore, the more stable the carbocation that is formed the faster the reaction occurs. In this reaction, reactive alkyl halides are converted into ethers.

positive test

In this reaction the silver ion is reduced to metallic silver which deposits as a mirror on the inside of a warm test tube. Carbonyl compounds other than aldehydes do not react with this reagent. Old mirrors were once made using the Tollens' reagent.

alcohols -what test do we use?

Lucas test

what do we use if we're extracting an acid with pKa lower than 6, like carboxylic acids?

NaHCO3

Sn2 test reagents

NaI/Acetone

what do we use if we're extracting an acid with a pKa lower than 15 for example carboxylic acids and phenols?

NaOH. A stronger base for a weaker acid

Lucas test HCl/ZnCl2

The Lucas test involves the treatment of an alcohol with a solution of zinc chloride in concentrated hydrochloric acid. This test converts the alcohol into its corresponding alkyl chloride. The alkyl chlorides formed are insoluble in the aqueous solution and give a turbid suspension. The test is limited to those lower molecular weight alcohols (up to 5 or 6 carbons) that are soluble in the aqueous solution; however, insoluble alcohols react to form alkyl chlorides but cannot be distinguished as a positive result. Phenols do not react with Lucas reagent.

positive test

The bromine solution is a red-brown color. When an alkene is added to the bromine solution the solution turns colorless and this indicates a positive test.

SN1 test -what is the positive test?

The formation of silver chloride, AgCl, as a white solid indicates a positive test.

stereochemistry

This is a one-step, concerted-mechanism that results in the inversion of configuration because of backside nucleophilic attack. The inversion of configuration also causes a change in stereochemistry if the starting material and product are chiral.

Aldehydes and Ketones -what test is used for these?

Tollens' Silver Mirror Test for Aldehydes

positive test

When the oxidation occurs the orange color of the Jones reagent, Cr(VI), changes to the dark green of Cr3+. This change in color indicates a positive test. Also, tertiary alcohols do not undergo Jones oxidation because the carbon atom bearing the hydroxyl group lacks a hydrogen.

positive test -Ferric chloride (FeCl3) is colorless or slightly orange in color. When FeCl3 reacts with stable enols and phenols a colored complex is formed. Therefore, a positive test is:

a change in color to red, blue, purple, or green.

If compound is soluble in water then ______ extraction is not the appropriate method **possibly question on midterm

acid-base

________ and _________ are also oxidized by the Jones reagent

aldehydes phenols **this doesn't fit the trend but sometimes shows up

2,4-Dinitrophenylhydrazine—(2,4-DNP) **you will need to memorize this structure The 2,4-DNP reagent reacts positively ONLY with________ and no other carbonyl-containing compounds like esters, amides, or carboxylic acids.

aldehydes and ketones

Ferric chloride test -Aldehydes and ketones with an _________ can undergo an equilibrium called tautomerization (isomerization) to form enols: -what form is formed most often int his reaction? Keto or enol

alpha-hydrogen keto

electronegativity and size trend on the periodic table

electron increases up and to the right, size increases down and to the left

difference bw SN1 and SN2

in main step (substitution) SN1 = 2 steps and SN2 = 1 step

as acidity increases what happens to basicity?

it decreases

order of reactivity pic

least statically hindered alkyl chloride will act first. tertiary are too hindered. The ones that don't react are too hindered. Here primary is best

which compounds are soluble in water?

polar, since water is polar. Remember, like dissolves like

what are the types of chromatography

solid-liquid—thin layer chromatography (TLC) and column chromatography liquid-liquid—high pressure liquid chromatography (HPLC) gas-liquid—gas chromatography (GC)