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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.