Passage
Students used three classification tests to study the reactivity of alcohol, aldehyde, and ketone functional groups in organic compounds. The organic compounds provided to the students are given in Table 1.Table 1 Organic Compounds Tested
First, the students performed the Lucas test by mixing a few drops of each compound with 2 mL of the Lucas reagent (ZnCl₂ and HCl) . This reagent is used to test for secondary and tertiary alcohols. A positive test result is indicated by a cloudy reaction mixture upon addition of the Lucas reagent due to the formation of an insoluble compound by an S_N1 reaction with a secondary or tertiary alcohol (Reaction 1) .
Reaction 1Next, a test for alcohols and aldehydes was performed by the addition of a drop of chromic acid reagent (CrO₃ dissolved in aqueous H₂SO₄) into samples of the organic compounds. The disappearance of the orange color from chromic acid and formation of a blue-green suspension is indicative of a positive result for this test. Compound A was found to be an example of a positive result, as shown in Reaction 2.
Reaction 2Finally, samples of the compounds were also dissolved in water, followed by the addition of NaOH and iodine. This test is known as the iodoform test, which is used to identify methyl ketones and secondary alcohols. A positive result is indicated by the formation of iodoform (CHI₃) , a yellow precipitate (Reaction 3) .
3Table 2 Selected Observations from the Classification Tests

-Compound D gives a positive result for the chromic acid test. What is the structure of the product formed by the reaction of Compound D with the chromic acid reagent?

Question

Passage
Students used three classification tests to study the reactivity of alcohol, aldehyde, and ketone functional groups in organic compounds. The organic compounds provided to the students are given in Table 1.Table 1 Organic Compounds Tested

First, the students performed the Lucas test by mixing a few drops of each compound with 2 mL of the Lucas reagent (ZnCl₂ and HCl) . This reagent is used to test for secondary and tertiary alcohols. A positive test result is indicated by a cloudy reaction mixture upon addition of the Lucas reagent due to the formation of an insoluble compound by an S_N1 reaction with a secondary or tertiary alcohol (Reaction 1) .

Reaction 1Next, a test for alcohols and aldehydes was performed by the addition of a drop of chromic acid reagent (CrO₃ dissolved in aqueous H₂SO₄) into samples of the organic compounds. The disappearance of the orange color from chromic acid and formation of a blue-green suspension is indicative of a positive result for this test. Compound A was found to be an example of a positive result, as shown in Reaction 2.

Reaction 2Finally, samples of the compounds were also dissolved in water, followed by the addition of NaOH and iodine. This test is known as the iodoform test, which is used to identify methyl ketones and secondary alcohols. A positive result is indicated by the formation of iodoform (CHI₃) , a yellow precipitate (Reaction 3) .

3Table 2 Selected Observations from the Classification Tests

-Compound D gives a positive result for the chromic acid test. What is the structure of the product formed by the reaction of Compound D with the chromic acid reagent?

Quizplus · Accepted Answer

11ecba2d_1290_b210_a3bf_d1d7323c023e_MD0008_00 Oxidation of an organic molecule often involves a decrease in the number of C-H bonds and an increase in the number of C-O bonds. Oxidizing agents will convert primary alcohols to carboxylic acids (except PCC, which converts primary alcohols to aldehydes), secondary alcohols to ketones, and aldehydes to carboxylic acids. The passage demonstrates that when a secondary alcohol gives a positive result in the chromic acid test, it is converted to a ketone in the process. The increase in the number of C-O bonds as a result of reaction indicates that the chromic acid test is an oxidation. Compound D is a four-carbon aldehyde (butanal), and the question states that it gives a positive result for the chromic acid test (meaning it is oxidized). Aldehydes already have two C-O bonds (as a C=O group), but when aldehydes are oxidized, they form a compound with an additional C-O bond (a carboxylic acid). Therefore, a four-carbon carboxylic acid will be produced when Compound D reacts with the chromic acid reagent. (Choice B) Formation of 1-butanol would result from a reduction rather than an oxidation. (Choice C) This compound is a ketone, which would result from the oxidation of a secondary alcohol rather than an aldehyde. (Choice D) This compound is the aldehyde butanal (the same as Compound D). Because Compound D gives a positive result for the chromic acid test, it must be transformed by oxidation into a new compound rather than remain unchanged. Educational objective: Oxidation of organic molecules often increases the number of C-O bonds and decreases the number of C-H bonds in the molecule. Oxidizing agents, such as chromic acid, will convert primary alcohols to aldehydes, secondary alcohols to ketones, and aldehydes to carboxylic acids.

Passage Students Used Three Classification Tests to Study the Reactivity of of Alcohol