Two compounds, A and B, have the formula of C3H6O. Determine their condensed structural formulas and names....

Question

using the following test results.

Compound A forms a red-orange precipitate with Benedict's reagent, but does not react with iodoform.

Compound B forms a yellow solid in the iodoform test, but does not react with Benedict's reagent.

I am having a hard time doing this. I need help please.

Answer 1

The C:H:O ratio, and the chemical tests tells you that you you must have a carbonyl in there- if it were an alcohol there would be 2 more hydrogens. So, how many different arrangements of 3 carbon atoms can you get?
Only 1: A chain of 3.
Somewhere on this chain, resides a carbonyl substituent.
The first test shows a reaction with Benedict's soln, but not iodoform. The reaction with Benedict's soln tells you there is a carbonyl present, but it does not react with Iodoform. If it doesn't react with iodoform, there is no C(O)CH3 functionality, as this is what iodoform tests for. So, it cannot be CH3C(O)CH3. Therefore, it must be the aldehyde: CH3CH2C(O)H. The second compound does react with iodoform, so it must in fact be the ketone: CH3C(O)CH3.
So, A = propanal, B = propanone