Question

a student was given from the list of the compounds below a, b and d blindly and asked to identify them. he treated each of them with bradys reagent (2,4 - dinitrophenylhydrazine) and isolated a bright yellow compound for one of them, but the other two gave false negatives. the student reasoned that the false negatives may be due to sterics and, on further thinking, it dawned on him that he might be able to rule out one of the false negatives with the haloform test. what compound did he find compatible with the haloform test? that compound did indeed give a false negative in the brady test. which of the other two was positive in the brady test? clear my selection a = brady d = haloform b = haloform a = haloform b = brady d = haloform a = brady d = brady b = haloform

Explanation:

Step1: Recall test - reagent characteristics

The Brady's reagent (2,4 - dinitrophenylhydrazine) reacts with carbonyl compounds (aldehydes and ketones) to form 2,4 - dinitrophenylhydrazone derivatives which are bright - yellow to orange precipitates. The haloform test is positive for methyl - ketones ($R - CO - CH_3$) and certain secondary alcohols that can be oxidized to methyl - ketones.

Step2: Analyze false - negative scenarios

A compound that is not an aldehyde or ketone will give a false - negative in the Brady's test. A compound that is not a methyl - ketone or a suitable secondary alcohol will give a false - negative in the haloform test.

Step3: Evaluate each option

If one compound is not a carbonyl compound (so false - negative in Brady's test) and the other is not a methyl - ketone (so false - negative in haloform test), we can make the identifications. For example, if A is not a carbonyl (false - negative in Brady) and B is not a methyl - ketone (false - negative in haloform), we can rule out compounds based on their negative test results.

Answer:

A = Brady, B = haloform