Aldehydes, Ketone, and Carbohydrates Flashcards
ketones and aldehydes with fewer than five carbon atoms are soluble in water and form neutral solutions (pH = 7)
True or False
True
Aldehydes and ketones with 5<C<9 are soluble in water, 5% NaOH and 5% HCL but soluble in concentrated H2SO4 (Class N)
True or False
False (They are insoluble in water)
2,4 - DNP Test are test for aldehydes and ketones
True ore False
True
2,4 - DNp Test reagent
2,4 - dinitrophenylhydrazine
Positive Result: Formation of yellow or orange-red precipitate
2,4 - DNp Test reagent
General test for the presence of the carbon-oxygen double bond.
2,4 - DNp Test reagent
Formation of an orange or yellow precipitate from a carbon-oxygen double bond in an aldehyde or ketone
2,4 - DNp Test reagent
It help to identify the specific aldehyde or ketone (recrystallization, purification, and MP determination)
2,4 - DNp Test reagent
Complications: some ketones give oils which will not solidify, some allylic alcohols are oxidized by the reagent to aldehydes and ketones and give positive results; some not pure alcohols may contain aldehyde or ketone impurities.
2,4 - DNp Test reagent
A C-H bond on the a-carbon to a carbonyl group is more acidic than many other C-H bonds, because reaction with base forms a resonance - stabilized enolate anion.
Haloform Reaction
Enolates are ________, and so they react with _______ to form new bonds on the a-carbon.
nucleophiles and electrophiles
Halogenation of methyl ketones in base to form ______. (Haloform Reaction)
iodoform (HCl3)
In the haloform reaction, the reaction occurs with methyl ketones and results in cleavage of a carbon-carbon σ bond.
True or False
True
Iodoform Test for Methyl Ketone is test for acetaldehyde and methyl ketones
True or False
True
Positive result: formation of a yellow precipitate or suspension of iodoform and a distinct smell
Iodoform Test for Methyl Ketone
Complication: The reaction also gives a positive result with secondary alcohols of the type RCH(OH)CH3 because they are oxidized under the reaction conditions to methyl ketones.
Iodoform Test for Methyl Ketone
Oxidation - Aldehydes are readily oxidized to carboxylic acids whereas ketones cannot be readily oxidized (under acidic conditions) True or False
True
This difference (oxidation) forms the basis of the tests for distinguishing aldehydes and ketones
True or False
True
Under alkaline condition, a ______ is formed instead
salt
Tollen’s Test is test for aldehydes
True or False
True
reagent: Ammoniacal silver nitrate
Tollen’s Test
Positive Test: formation of elemental silver, accumulated onto the inner surface of the reaction vessel, producing a silver mirror in the inner surface of the vessel
Tollen’s Test
Complications: The tube must be clean and oil-free if a silver mirror is to be observed.
Tollen’s Test
In Tollen’s Test, Aromatic amine and some phenols are easily oxidized which give a positive results
True or False
False (it gives a false positive result)
Fehling’s Test is a test for ketones
True or False
False (it is a test for aldehydes)
Reagent: Fehling’s solution A (CuSO4) and Fehling’s solution B (sodium potassium tartrate or Rochelle salt and strong alkali - NaOH)
Fehling’s Test
Positive results: formation of red precipitate (cuprous oxide)
Fehling’s Test
Purpald Test reacts with aldehydes to form a cyclic derivatives
True or False
True
Reagent: 4-amino-5-mercapto-1,2,4-triazole (heterocyclic compounds)
Purpald Test
In Purpald Test, the cyclic derivative is then _________ by exposure to air and forms an intensely colored (usually purple) product.
oxidized
Jones Test is a test for ketones
False (test for aldehydes)
Reagent: CrO3/H2SO4
Jones Test
Positive Results: disappearance of orange color (Jone’s reagent) and appearance of greenish precipitate
Jones Test
In Jones Test, ________ are rapidly oxidized to carboxylic acids
Aldehydes
Complication: The color usually develops in 5-15 seconds
Jones Test
Schiff’s Test is a test for aldehydes
True or False
True
reagent: Schiff’s reagent
Schiff’s Test
Positive results: appearance of pink or magenta color
Schiff’s Test
m-dinitrobenzene Test is a test for ketones
True or False
True
Reagent: m-dinitrobenzene
m-dinitrobenzene Test
Positive results: appearance of violet color
m-dinitrobenzene Test
Rothera’s Test is a test for aldehydes
True or False
False ( for ketones)
Reagent: sodium nitroprusside in alkaline medium
Rothera’s Test
Positive results: appearance of red color complex
Rothera’s Test
It is the polyhydroxy aldehydes or ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones
Carbohydrates
Aldehydes and ketones are simple
compounds which contain a
_________ - a carbon-oxygen
double bond.
carbonyl group
The carbonyl group has a hydrogen
atom attached to it together with
either:
- a second hydrogen atom or
- a hydrocarbon group which
might be an alkyl group or one
containing a benzene ring.
Aldehydes
The carbonyl group has two
hydrocarbon groups attached.
Ketones
reagent: I2/NaOH
Iodoform Test for Methyl Ketone
consist of 3-7 C atoms. classified as either aldoses or ketoses
ketoses
Monosaccharides (Simple Sugars)
two monosaccharide units linked by a glycosidic bond. Classified as reducing or non-reducing disaccharides
Disaccharides
consist of ten to thousands of monosaccharide units
Polysaccharides
Benedict’s Test is a test for reducing sugars
True or False
True
positive result: formation of yellow, yellow-green, orange or brick-red precipitate
Benedict’s Test
Reagent: Benedict’s Reagent
Benedict’s Test
Reduction test for carbohydrates
Benedict’s Test
The free aldehyde or keto group in the reducing sugars reduce cupric hydroxide in alkaline medium to red colored cuprous oxide.
True or False
True
Depending on the _______ of ________, yellow to green color is developed
concentration of sugars
All _________ are reducing sugars as they all have a free reactive carbonyl group.
monosaccharides
Some disaccharides, i.e. reducing disaccharides, have exposed carbonyl groups but less reactive than monosaccharides
True or False
True