Exam 2 Labs

In the reaction of benzaldehyde and potassium hydroxide, what is the source of energy for the reaction?

Grinding the reactants together provides mechanical energy.

Properties

In general, alcohols dissolve when mixed with water because the O-H bonds in alcohols can hydrogen bond with water.

Cannizzaro reaction

In the Cannizzaro reaction, added hydroxide is a reagent because it is incorporated into the product.

Cannizzaro reaction step

In the first step of a Cannizzaro reaction, such as benzaldehyde with base, the hydroxide attacks the carbon of the carbonyl group because that position is partially positive.

Consider the Cannizzaro reaction of benzaldehyde.

In the reaction, benzaldehyde is reduced to form benzyl alcohol and benzaldehyde is oxidized to form benzoate.

Determine whether each phrase describes carboxylic acids or esters.

Notable for their pleasant fragrances = Esters Their reactions with base are known as saponifications = Esters Form hydrogen bonds amongst themselves and have lower vapor pressure = Carboxylic acids Do not form hydrogen bonds amongst themselves and have higher vapor pressure = Esters Their reactions with base are known as neutralizations = Carboxylic acids Usually have a sour odor = Carboxylic acids

Denaturing is the process of interrupting a protein's structure so that it no longer functions. Which level of structure is NOT affected by denaturing a protein?

Primary structure

Identify the level of protein structure matching each description.

Small 3D features determined by hydrogen bonding = 2 structure Interaction of multiple of protein units = 4 structure Overall 3D shape of a protein = 3 structure The sequence of amino acids = 1 structure

What is chromatography?

A technique to separate mixtures based on the molecular properties of the involved chemicals

Which solvent is NOT appropriate to use in Tollens's test?

Acetaldehyde because it is an aldehyde. Because the test reacts with aldehydes, acetaldehyde would give a false positive result.

Which solvent is NOT appropriate to use in the 2,4-DNP test?

Acetone because it is a ketone. Because the test reacts with aldehydes and ketones, acetone would give a false positive result.

Aspirin synthesis involves the addition of an acetyl group to salicylic acid in a condensation reaction with an alcohol. The acetyl group could be added with a carboxylic acid but the preferred procedure is to use the acid anhydride. Why is preferable to use an acid anhydride for ester formation with an alcohol rather than a carboxylic acid?

Acid anhydrides are less stable than esters so the equilibrium favors the ester product.

How can you remove the protein casein from a sample of non-fat milk?

Add acid to change the protein's tertiary structure, which triggers solid formation.

Multiple reagents or changes can denature a protein. Which listed change will NOT denature a protein?

Adding water

Consider the reaction of benzaldehyde and hydroxide.

After completing the reaction, both water and acid need to be added. Then, the reaction mixture is filtered, isolating benzoic acid on the filter because benzyl alcohol is more soluble in water.

Which pair of functional groups would be easiest to distinguish using their IR spectra?

Ether, like 1-butoxybutane, and ester, like butyl butanoate

2,4-DNP test

The 2,4-DNP test shows the presence of aldehydes and ketones. A positive 2,4-DNP test appears as a yellowish precipitate. A negative 2,4-DNP test appears as an orange solution.

The Lucas test (cont)

The Lucas test has different results based on the type of alcohol present because the reaction involves a carbocation intermediate, which is more stable for tertiary alcohols compared to primary alcohols. Therefore, tertiary alcohols react faster than primary alcohols.

Describe the complete role of the acid catalyst in the rearrangement of pinacol.

The acid protonates a hydroxyl group and then the conjugate base deprotonates an oxygen after rearrangement.

Ninhydrin Test

The ninhydrin test shows the presence of amino acids. A positive ninhydrin test appears as a color change to purple. A negative ninhydrin test appears as a colorless solution.

Periodic acid test

The periodic acid test shows the presence of diols. A positive periodic acid test appears as a white precipitate. In addition to periodic acid, silver nitrate is also needed to complete the test.

Why does the pinacol rearrangement more often use sulfuric acid, as the acid catalyst rather than hydrochloric acid?

The presence of the chloride ion could result in a competing substitution reaction.

Some reactions can be performed without a solvent. What are the benefits of not needing a solvent in a reaction?

The reaction often costs less because solvents can be expensive. Less chemical waste is generated because there are not solvents to remove.

rearrangement of pinacol

The rearrangement of pinacol occurs in the cation intermediate after losing water as a leaving group. The cation is originally located on the carbon that lost the leaving group. However, the cation is more stable on the carbon with the remaining alcohol group. Therefore, the rearrangement is shifting a substituent from one carbon to another to create the more stable cation.

Consider the structures of benzaldehyde and benzyl alcohol.

These two structures can be distinguished by proton NMR. The hydrogen of the aldehyde group will appear downfield between 9 and 11 ppm and there is no equivalent peak for the alcohol. Also, the methylene hydrogens in the benzyl position of the alcohol will be the only significant upfield between 0 and 3 ppm peak between the two structures.

Tollens's test

Tollens's test shows the presence of aldehydes. A positive Tollens's test appears as a silver precipitate. A negative Tollens's test appears as a colorless solution.

Octyl formate is an ester that has the flavor of oranges. It can be synthesized from an alcohol and a carboxylic acid.

What alcohol is needed to make octyl formate? Octanol What carboxylic acid is needed to make octyl formate? Formic acid

Which species will have an IR spectrum?

Carbon dioxide Water vapor Methane

Which solvent is appropriate to use in the iodoform test?

Dioxane The iodoform test gives a positive result with the methyl aldehyde, which is acetaldehyde, methyl ketones, like acetone, and alcohols with alpha methyls, like ethanol. Therefore, the only appropriate solvent on this list is dioxane, an ether.

Formation of ester

The molecules that will be combined to form an ester are a carboxylic acid and an alcohol.

Biuret test

Biuret test shows the presence of a tripeptide or larger peptide. A positive Biuret test appears as a violet solution. A negative Biuret test appears as a blue solution.

Jones's test / Chromic acid test

Jones's test, also known as the chromic acid test, shows the presence of primary or secondary alcohols. A positive Jones's test appears as a color change to green. A negative Jones's test appears as an orange solution.

Lucas's test

Lucas's test shows the presence of alcohols. A positive Lucas's test appears as an insoluble oil. A negative Lucas's test appears as a colorless solution.

Many tests to distinguish aldehydes and ketones involve the addition of an oxidant.

Only aldehydes can be easily oxidized because there is a hydrogen next to the carbonyl and oxidation does not require breaking C-C bonds.

Aspartame is the methyl ester of a dipeptide made of phenylalanine and aspartic acid. What are the expected products of the hydrolysis of aspartame?

Phenylalanine Aspartic acid Methanol

ceric ammonium nitrate (CAN) test

The ceric ammonium nitrate (CAN) test shows the presence of aliphatic alcohols. A positive CAN test appears as a color change to red. A negative CAN test appears as a yellowish solution.

Which solvent is NOT appropriate to use in Jones's test?

The common solvent of ethanol is not appropriate for Jones's test because it is an alcohol. Because the test reacts with alcohols, ethanol would give a false positive result.

If the rearrangement of pinacol is successful, what changes would be seen in the IR spectrum for the product compared to the starting material?

The disappearance of an O-H band from the starting material The addition of a C-O double bond band in the product The disappearance of a C-O single bond band from the starting material

ferric chloride test

The ferric chloride test shows the presence of phenols. A positive ferric chloride test appears as a color change to purple. A negative ferric chloride test appears as a colorless solution.

Iodoform Test

The iodoform test shows the presence of alcohols with an alpha methyl group. A positive iodoform test appears as a yellow precipitate. A negative iodoform test appears as a colorless solution.

Iodoform test

The iodoform test shows the presence of methyl ketones. A positive iodoform test appears as a yellow precipitate. A negative iodoform test appears as a colorless solution.

Iodoform Test

The iodoform test shows the presence of methyl ketones. A positive iodoform test appears as a yellow precipitate. A negative iodoform test appears as a colorless solution.

The Tollen's test is the reaction of aldehydes with silver(I) ions in basic solution to form silver metal and a carboxylate.

Which species is being oxidized in the reaction? Aldehyde Which species is being reduced in the reaction? Silver(I) ion Which species is the visual indicator of a positive test? Silver metal