Cruz, Patricia Anne D.

De Guzman, Anne K.

Dela Cruz, Maria VictoriaDuron, Marc John

CHM143L / GROUP 2

Professor Oliver Villaflores

Introduction to Carbonyl compounds

A compound containing the carbonyl group is known as a carbonyl compound

Carbonyl group - a functional group composed of a carbon atom double-bonded to an oxygen atom

The carbon and oxygen atoms of the carbonyl group are sp2 hybridized and planar in geometry

This generally undergoes nucleophilic substitution, triggering an attack at 107

The carbonyl group is treated as an electrophiledue to resonance and inductive effects:

The resonance structure show a positive charge on the carbonyl carbon (lack of electron density)

Due to the electronegativity of the oxygen atom, induction renders the carbon atom partially

positive

ALDEHYDE

A simple type of carbonyl compound

with at least one hydrogen atom as a

substituent

KETONE

A simple type of carbonyl

compound with two substituent other than the hydrogen atom

The difference between aldehydes and ketones

Aldehydes are more reactive than ketonestoward nucleophilic attack:

Steric effects: ketone is more stericallyhindered than aldehyde

Electronic effects: The partial positive charge of an aldehyde is less stabilized than that of a ketone:

Classifying carbonyl compounds:

CHEMICAL TESTSThe ease of oxidation helps chemists distinguish aldehydes from ketones.

Aldehydes are easily oxidized by all sorts of different oxidizing agents, ketones aren't.

1. Benedicts test

Benedict's solution contains copper(II) ions complexed with citrate ions in sodium carbonate solution. Benedicts reagent

has Cu2+ ions which gives it a deep blue color.During the oxidation, Cu2+ is reduced to Cu2O (a precipitate).If the blue color does not change no oxidation occurs. If the

blue color stays and you have a precipitate, oxidation occurs.

Benedicts test continued

POSITIVE RESULT: ketone

No change in the blue solution.aldehyde

The blue solution produces a dark red precipitate

Classifying carbonyl compounds:CHEMICAL TESTS

2. Tollens testTollens reagent, is an alkaline solution of silver (Ag+) ion complexed with ammonia (NH3), which keeps the Ag

+ ion in solution.

When Tollens reagent oxidizes an aldehyde, the Ag+ ion is reduced to free silver (Ag). Deposited on a clean glass

surface, the silver produces a mirror.

Tollens test continued

RESULTS:

ketoneNo change in the colorless solution.

aldehydeThe colorless solution produces a silver

mirror on the test tube. Less spectacular, but just as valid is the formation of a grey or

black precipitate.

CHEMICAL TESTS3. Carbonyl group reactions

Condensation Reaction

REAGENT/S and USES: 2,4-dinitrophenylhydrazine - utilized as a test for the carbon-oxygen double bond in

ketones and aldehydes

MECHANISM: Nucleophilic addition-elimination rxn.

The 2,4-dinitrophenylhydrazine first adds across the carbon-oxygen double bond (the

addition stage) to give an intermediate compound which then loses a molecule of

water (the elimination stage).

POSITIVE RESULT: A bright orange or yellow precipitate

shows the presence of the carbon-oxygen double bond in an

aldehyde or ketone.

CHEMICAL TESTS

- Addition Reaction

REAGENT/S and USES: Sodium bisulfite (NaHSO3)- utilized as a test for the carbon-oxygen double bond in

conjunction with the condensation rxn.

MECHANISM: Addition reaction

POSITIVE RESULT: Formation of white

crystals (precipitate) indicating presence of

C=O group

This reaction only works well for aldehydes. In the case of ketones, one of the hydrocarbon

groups attached to the carbonyl group needs to be a methyl group. Bulky groups attached to the

carbonyl group get in the way of the reaction happening. The reason that cyclohexanone react with sodium bisulfite and not in 3-pentanone is

that cyclohexanone is an unhindered ketonewhile 3-pentanone only has ethyl groups and

this is already bulky enough to interfere with the reaction.

3. Carbonyl group reactions

2,4-dinitrophenylhydrazine test

Sodium bisulfite test

CHEMICAL TESTS

5. Alkyl group reactions Haloform reaction

The haloform reaction is the reaction ofa methyl ketone with chlorine, bromine, oriodine in the presence of hydroxide ions togive a carboxylate ion and a haloform. Thereis one aldehyde that undergoes the haloformreaction, which is acetaldehyde.

Iodoform Test

When the halogen used is iodine.

1. TEST COMPOUNDS OBSERVATIONSAcetaldehyde

Acetaldehyde+H2O+8M NaOH-Pale Yellow+ I2 in KI- Golden Yellow+heat- pale yellow precipitate

AcetoneAcetone+H2O+8M NaOH-Clear+ I2 in KI- Pale Yellow+heat- pale yellow precipitate

References

Klein, David M. Organic Chemistry 2nd

Ed. 2012 John Wiley and Sons, Inc.