carbonyl compounds

Question 1

What is benzaldehyde? (describe its structure)

Answer 1

It has a benzene ring directly bonded to a carbonyl carbon.

Question 2

What is Fehling’s reagent used to test for? State the positive observations.

Answer 2

Aliphatic aldehydes. Reddish-brown copper II oxide ppt.

Question 3

What is Tollen’s reagent used to test for? State the positive observations.

Answer 3

Aldehydes. Silver mirror / grey ppt.

Question 4

What is 2,4-DNPH used to test for? State the positive observations.

Answer 4

Carbonyl compounds. (ketones and aldehydes)
Orange ppt (2,4-dinitrophenylhydrazone)

Question 5

What is the ratio of the iodoform test for carbonyl compounds with the methylketo group?

Answer 5

3:6:3:5
(iodine, OH-, iodide, water)

Question 6

What is the positive result for the iodoform test? What is the product that gives the positive result?

Answer 6

Yellow ppt (CHI3)

Question 7

When do you use K2Cr2O7 as an oxidising agent? (instead of KMnO4)

Answer 7

When you want to prevent further oxidation.
e.g. forming aldehyde from alcohol, forming methanoic acid from methanal, forming ethanoic acid from ethanal. (note: all 3 products are prone to further oxidation, hence a MILDER O.A. must be used)

Question 8

On which atom is the lone pair indicated for CN- nucleophile?

Answer 8

on the carbon atom, NOT the nitrogen atom.