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Chapter 20: Q45P (page 1078)

(A true story) The manager of an organic chemistry stockroom prepared unknowns for“Ketones and Aldehydes” experiment by placing two drops of the liquid unknowns in test tubes and storing the test tubes for several days until they were needed. One of the unknowns was misidentified by every student. This unknown was taken from a bottle marked “Heptaldehyde.” The stockroom manager took an IR spectrum of the liquid in the bottle and found a sharp carbonyl stretch around and small, sharp peaks around 2710 and . The students complained that their spectra showed no peaks at 2710 or , but a broad absorption centered over the region and a carbonyl peak around . They also maintained that their samples are soluble in dilute aqueous sodium hydroxide.

(a)Identify the compound in the stockroom manager’s bottle and the compound in the students’ test tubes.

(b)Explain the discrepancy between the stockroom manager’s spectrum and the students’ results.

(c)Suggest how this misunderstanding might be prevented in the future.

Short Answer

Expert verified

(a)

(b) The difference between the two samples is one is aldehyde and another is a carboxylic acid.

(c) The problem can be prevented by keeping in an inert atmosphere or preparing fresh unknown samples.

Step by step solution

01

About heptaldehyde

The organic compound that bears seven carbons in the parent chain with the aldehyde group is heptaldehyde.There are some wavelength values for the identification of such compounds when they are present with substituents.

02

(a) About the structures

The structure in the stock bottle consists of an aldehyde group. The structure is shown below.

The structure in the student’s sample contains the carboxylic acid group. The structure is given below.

03

(b) About the difference

The student sample structure has carboxylic acid and the stock bottle contains aldehyde. The contact with oxygen present in the air gets oxidized to the highly sensitive aldehyde group to acid conversion.

04

(c) About the prevention

The prevention can be done by storing the aldehyde in an inert atmosphere for example nitrogen or argon, which will prevent oxidation reaction. Also, the preparation of fresh unknowns will help in the prevention.

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Most popular questions from this chapter

Glutathione (GSH) is a tripeptide that serves as a mild reducing agent to detoxify peroxides and maintain the cysteine residues of hemoglobin and other red blood cell proteins in the reduced state. Complete hydrolysis of glutathione gives Gly, Glu, and Cys. Treatment of glutathione with carboxypeptidase gives glycine as the first free amino acid released. Treatment of glutathione with 2,4-dinitrofluorobenzene (Sanger reagent, Problem 24-21, page 1282), followed by complete hydrolysis, gives the 2,4-dinitrophenyl derivative of glutamic acid. Treatment of glutathione with phenyl isothiocyanate does not give a recognizable phenylthiohydantoin, however.

(a) Propose a structure for glutathione consistent with this information. Why would glutathione fail to give a normal product from Edman degradation, even though it gives a normal product from the Sanger reagent followed by hydrolysis?

(b) Oxidation of glutathione forms glutathione disulfide(GSSG). Propose a structure for glutathione disulfide, and write a balanced equation for the reaction of glutathione with hydrogen peroxide.

Most of the Fischer esterification mechanism is identical with the mechanism of acetal formation. The difference is in the final step, where a resonance-stabilized carbocation loses a proton to give the ester. Write mechanisms for the following reactions, with the comparable steps directly above and below each other. Explain why the final step of the esterification (proton loss) cannot occur in acetal formation, and show what happens instead.

Question. Cellosolve® is the trade name for 2-ethoxyethanol, a common industrial solvent. This compound is produced in chemical plants that use ethylene as their only organic feedstock. Show how you would accomplish this industrial process.

Question: Arrange each group of compounds in order of increasing basicity.

  1. CH3COO-,CICH2C00- , and PhO-
  2. sodium acetylide, sodium amide, and sodium acetate
  3. sodium benzoate, sodium ethoxide, and sodium phenoxide
  4. pyridine, sodium ethoxide, and sodium acetate

Question:

  1. Determine the structure of the carboxylic acid whose proton NMR spectrum appears below.
  2. Draw the NMR spectrum you would expect from the corresponding aldehyde whose oxidation gives this carboxylic acid.
  3. Point out two distinctive differences in the spectra of the aldehyde and the acid.
See all solutions

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