CHEM 238 FINAL

What conditions does the hydrolysis of an amide bond occur?

Amide hydrolysis occurs under acidic or basic conditions Reactants must be heated for hydrolysis to occur

What two amino acids contribute to the structure of aspartame?

Aspartic acid and phenylalanine

Secondary protein structure

Beta pleated sheet is held together by hydrogen bonds between adjacent segments. Secondary level of protein structure refers to the spatial arrangements of short segments of protein. In a beta pleated sheet, side chains extend above and below sheet.

Four major methods of purification

Chromatography, extraction, distillation, and recrystallization

Why is potassium permanganate a better choice as a classification test reagent than chromic acid to detect the methanol produced by aspartame hydrolysis?

Chromic acid oxidizes amino acids and will give false positive color changes. Potassium permanganate loses its purple color as it oxidizes alcohols, so the reaction can be followed visually.

POLYMERS: polyester polysaccharide polyamide

Dacron 54, Dacron 64, Cotton Nylon 66, Wool, Silk

Exp. 4-Grignard Reaction What is purpose of saturated sodium chloride sol'n?

Decreases the solubility of the organic product in water.

What color of visible light does tetraphenylcyclo-pentadienone absorb? Transmit?

Green; purple

Diethyl Ether

Has low miscibility in water; low ability to mix homogeneously.

How to carry out a Fischer esterification?

Heating a carboxylic acid in an alcohol solution containing a small amount of a strong acid catalyst. Carboxylic acids are not reactive enough to be attacked by neutral alcohol, but are made more reactive in presence of mineral acid (H2SO4). Heat is also needed.

What happens for a positive test result for the Tollen's test?

Silver mirror develops on inside of test tube.

In EXP. 1, what effect results if the filtrate solution is cooled too rapidly?

Small impure crystals will form

Components of Schiff's test

Sodium bisulfite, rosaniline hydrochloride

Components of iodoform test

Sodium hydroxide (NaOH), potassium iodide (KI), iodine

Sublimation

Solid --> gas phase

What happens for a positive test result for the Schiff's test?

Solution becomes red

Toxicity

Some of adverse effects resulting from exposure to material, usually by mouth, skin, or respiratory tract.

Rank molecules in terms of expected delta max in U.V. spectrum: (Longest --> shortest)

1,5-diphenyl-1,4-pentadie-3-one --> 1-phenyl-1-buten-3-one --> benaldehyde

Exp.5- Iodination of Salicylamide

1. Benzene and derivatives undergo electrophilic aromatic substitution reactions 2. Addition reaction with benzenes lead to loss of aromaticity. 3.Benzene and its derivatives undergo a type of substituion reaction in which a hydrogen tom is replaced by a substituent, but the stable aromatic benzene is regenerated at end of mechanism.

Calculating Percent Yield

1. Find the theoretical yield 2. (Actual yield of product/ Theoretical Yield of product) x 100

Calculating Theoretical Yield

1. Multiply the number of moles of reactant with the given mass. 2. Mol to mol ratio (usually 1:1) from reactant to product 3. Multiply the mole by the molar mass of the product

Beer's Law

A = EbC A: absorbance E: molar absorbance b: 1cm C: concentration

Only one aldehyde gives a positive test with iodoform test reagent. What is the aldehyde?

Acetaldehyde

Exp.4-Grignard Reaction Why is rinsing with acetone not suitable for drying glassware?

Acetone is ketone, the grignard reagents will react with the acetone to make unwanted byproduct.

Two uses of vacuum filtration setup

Drying a filtered solid, separation of a solution and a precipitate

Exp. 7 Causes: Glassware was not properly dried before reaction Lid was left off anhydrous alcohol bottle Excess of methanol was used Drying agent was added to the reaction flask

Effects: Less ester produced Less ester produced More ester produced More ester produced

What are esters, macrolides, and lactone?

Ester: carboxylic acid that contains a carbonyl group adjacent to ether linkage Macrolides: cyclic esters with more than nine carbons in the ring Lactone: cyclic esters

Lachrymator

Exposure to the chemical vapors will make you cry

As the concentration of the solution increases, the absorbance:

INCREASES

Exp.6-Aldehydes/ketones When performing iodoform test or DNP test, why should you avoid rinsing glassware with acetone prior to experiment?

It will give off a false positive for some carbonyl classification tests.

Relationship of value and magnitude of deltaH1 to stability of product

Large negative value of deltaH1 indicates stable product

Sodium Borohydride

Less reactive than lithium aluminum hydride, safest to use, used in reactions with methanol solvent Reduces aldehydes to primary alcohols, reduces ketones to secondary alcohols.

What is true of low molecular weight carboxylic acids?

Low molecular weight carboxylic acids are corrosive and irritants.

Exp. 4- Grignard Reaction What decreases the effectiveness of the Grignard Reaction?

Magnesium Ribbon was not wiped clean before use, glassware was not dried before use.

What tests positive for the iodoform test?

Methyl ketones and secondary methyl alcohol

Minimum and Maximum values of wavelength in UVA region?

Minimum: 315nm Maximum: 400nm

Molecules with least solubility in hot water?

Molecule with lowest ratio of hydrogen bonding components to hydrocarbon.

What functional groups are common to all amino acids?

NH2 and COOH

Exp. 8-Carboxylic acid and esters Fischer esterification was performed with acetic acid placed in test tube with ethanol and sulfuric acid. What were the two layers?

Organic (top) layer: ester Aqueous (bottom) layer: sulfuric acid, carboxylic acid, alcohol

What compounds will yield positive results for the permanaganate, ninhydrin, and ceric ammonium nitrate tests?

Permanganate: methanol, ethene Ninhydrin: aspartic acid, phenylalanine Ceric ammonium: methanol

Protein structure: primary structure secondary structure tertiary structure

Primary: unique sequence of amino acids joined by peptide bonds Secondary: coiled or folded structures. They are the alpha helix or beta pleated sheet. Tertiary: overall shape of single polypeptide unit. Ex: hydrogen bonds, ionic attractions, disulfide bridges, and hydrophobic interactions.

Exp. 7 Procedure: Boiling chips added to round bottom flask prior to reaction being heated under reflux. Reaction mix was washed with sodium carbonate Flask was fitted with a condenser and heated for twenty min. Concentrated sulfuric acid was added to the flask containing carboxylic acid and alcohol

Purpose: Reaction solvent is methanol, which bumps violently when heated. Unreacted carboxylic acid was neutralized Heating under reflux keeps reaction temperature high without evaporation Fischer esterification is catalyzed by acid, but water will push equilibrium back to reactant side.

Exp.9-Aldol Condensation Procedure: Reaction flask was heated under reflux on steam bath Grease all ground glass joints prior to heating under reflux UV spectrum was obtained within 30 seconds of preparing solution Hydroxide pellets were dissolved in absolute ethanol

Purpose: To minimize flammability risk associated with ethanol To avoid potassium hydroxide from seizing the glass pieces together Product has a very high molar extinction coefficient, and is sparingly soluble in hexane To exclude water from the reaction

Bond between carbon and magnesium is covalent and HIGHLY polarized. R-MgBr

R: negative charge MgBr: positive charge

Which of the following statements are true of ratio of products formed by reaction under thermodynamic control?

Ratio of products is not determined by relatives energies of transition states, ratio of products is determined by energies of products

Lithium Aluminum Hydride

Reduces esters. Reduces carboxylic acids to primary alcohols. Reduces aldehydes to primary alcohols, reduces ketones to secondary alcohols

What does the molar extinction coefficient (E) mean?

Strength at which a solution of sample absorbs light at a given wavelength

What effects the degree to which a dye will bind to a fabric and resist fading?

This depends on the number of available polar groups in the fabric polymer. Ex: Nylon is more polar than polypropylene.

In EXP. 1, what was the purpose of the initial hot vacuum filtration in the recrystallization process?

To remove insoluble solid impurities

True/False Azo dyes are stable Azo dyes are non-toxic Most azo dyes are not used as food coloring Leucoindigo is deep purple

True: Azo dyes are stable, non-toxic, and not used as food coloring.

True or false: Dichloromethane is flammable Methanol is flammable Concentrated sulfuric acid is corrosive 10% sodium carbonate solution must be used in fume hood Benzoyl Chloride is lachrymator

True: methanol is flammable, concentrated sulfuric acid is corrosive, benzoyl chloride is lachrymator.

UVA, UVB, and UVC characteristics

UVA: lowest energy wave, mild skin aging UVB: skin cancer UVC: highest energy wave, absorbed by earth's ozone layer, potentially lethal

How does adding a Bronsted acid help with Fischer esterification?

Water produced by the reaction is incapable of being a nucleophile for reverse reaction if it is protonated. Carbonyl group of carboxylic acid becomes more susceptible to attack by nucleophiles if carbonyl oxygen is protonated.

Ranking carboxylic acid derivatives according to their reactivity, from most reactive to least reactive.

Weaker basicity of leaving group, faster reaction proceeds.

Exp. 7 Evidence that the correct amount of drying agent was used.

When DCM solvent was dried by adding magnesium sulfate drying agent, the magnesium sulfate swirled around freely at bottom of flask.

When is recrystallization not a suitable method to purify an organic material?

When organic material is liquid instead of a solid

Trend of Fischer esterification?

Yield of ester increases as the branching in alcohol decreases.

Semi-empirical methods

faster to calculate than ab initio methods, some experimentally measured parameters are substituted into the calculation.