72 Questions
What is a common property of alkaloids?
They are colorless, crystalline solids
Why are most alkaloids considered chiral molecules?
To have nonsuperimposable mirror images
What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?
Free bases are insoluble in water but soluble in organic solvents
How do some alkaloids deviate from the general characteristics described in the text?
They can be liquid
Which amino acid is NOT listed as a precursor of true alkaloids in the text?
L-cysteine
What is responsible for the basic properties of alkaloids?
Presence of an unshared pair of electrons on the nitrogen atom
What is the typical nitrogen atom composition in alkaloids?
Usually contain one nitrogen atom
Which alkaloid is mentioned as an example of a pseudoalkaloid in the text?
Caffeine
In which category of alkaloids do mescaline and yohimbine belong according to the text?
Protoalkaloids
How are alkaloids converted into salts?
By treatment with acids
Which statement best describes the solubility of strychnine hydrochloride?
Much more soluble in water than as a base
What distinguishes quaternary ammonium compounds from amines in terms of chemical properties?
The presence of a positive charge balanced by a negative ion
What is the primary function of alkaloids in plants according to the text?
Protect against insects and herbivores
Which term describes alkaloids that contain nitrogen in heterocyclic ring systems?
Heterocyclic alkaloids
What reagent is commonly used to precipitate alkaloids from neutral or slightly acid solutions?
Mayer's reagent (potassium mercuric iodide solution)
What color does Dragendorff's reagent produce when precipitated with alkaloids?
Yellow
Where does the N atom in protoalkaloids like mescaline come from?
Amino acid precursors
How many organic groups are covalently bonded to the nitrogen in quaternary ammonium compounds?
Four
Which reagents give precipitates with proteins in the extraction of reddish-brown alkaloids?
Wagner's and Dragendorff's reagents
How is caffeine, unlike most alkaloids, usually detected?
By mixing with potassium chlorate and hydrochloric acid
What is the end result of exposing caffeine residue to ammonia vapor?
A purple color
Which amino acid does not have its COOH & NH2 groups on the same carbon atom?
Phenylalanine
What type of condensation occurs when a Schiff base reacts with a carbanion in alkaloid biosynthesis?
Mannich condensation
Which major amino acid is involved in the biosynthesis of alkaloids and has the structure different from other amino acids?
Anthranilic acid
What is the purpose of moistening the powdered material with alkaline substances in Method A of alkaloids extraction?
To combine with acids, tannins, and other phenolic substances
What is the final step in Method A of alkaloids extraction after shaking the organic liquid with aqueous acid?
Separation of alkaloid salts in the aqueous liquid
Why are organic solvents like ether or petroleum spirit used in alkaloids extraction?
To dissolve alkaloidal salts
What role do dilute acids play in Method B of alkaloids extraction?
To help extract the pigments and unwanted materials
Why are excess alkalis like sodium bicarbonate added in Method B of alkaloids extraction?
To precipitate the free alkaloids
In which method of alkaloids extraction is pigment removal specifically mentioned as a step?
Method B
What is a common property of alkaloids as described in the text?
They are generally chiral molecules
How many nitrogen atoms can alkaloids like ergotamine contain?
Up to five
What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?
Free bases are insoluble in water, salts are soluble
Which statement about alkaloids is true?
Alkaloids usually contain one nitrogen atom
How do alkalis like sodium bicarbonate play a role in Method B of alkaloids extraction?
Neutralize acidic solutions
What is the significance of alkaloids being chiral molecules?
It results in isomers with different chemical properties
What distinguishes protoalkaloids from true alkaloids based on the text?
Protoalkaloids have the N atom derived from an amino acid not part of the heterocyclic.
Why are pseudoalkaloids considered different from true and protoalkaloids?
Pseudoalkaloids can be derived from non-amino acid precursors.
What is the primary difference between typical alkaloids and atypical alkaloids according to the text?
Typical alkaloids contain nitrogen in aliphatic chains, while atypical alkaloids contain it in heterocyclic rings.
Which function do alkaloids primarily serve in plants?
Function as protective agents against insects and herbivores
What is a common characteristic shared by both true and pseudoalkaloids?
Both types are derived from amino acids.
Which compounds are examples of pseudoalkaloids according to the text?
Coniine and ephedrine
What is a distinguishing feature of caffeine, in terms of precipitation, compared to most alkaloids?
It does not precipitate like most alkaloids.
What amino acid involved in alkaloids biosynthesis has its COOH & NH2 groups not on the same carbon atom?
Anthranilic acid
Which reaction is NOT involved in the biosynthesis of alkaloids according to the text?
Hydrolysis
What is the primary role of potassium chlorate in detecting caffeine?
To aid in the color change during detection.
Which amino acid is NOT specifically mentioned as being involved in the biosynthesis of alkaloids?
Proline
What distinguishes reddish-brown alkaloids when extracted using Wagner's and Dragendorff's reagents?
They are denatured by evaporation.
What type of compounds are quaternary ammonium compounds such as tubocurarine chloride or muscarine chloride?
Neutral compounds
Which reagent is NOT commonly used for precipitating alkaloids from neutral or slightly acid solutions?
Fehling's reagent
What happens to the solubility of most alkaloids when precipitated with Mayer's reagent?
They remain insoluble
In the context of alkaloids, why are quaternary ammonium compounds unaffected by hydroxide ions?
They have no proton to give up
What distinguishes alkaloids like tubocurarine chloride or muscarine chloride from amines in terms of chemical properties?
Acidity
How do quaternary ammonium compounds like tubocurarine chloride or muscarine chloride differ from typical alkaloids in terms of chemical properties?
They are less reactive
What is the purpose of adding excess alkalis like sodium bicarbonate in Method B of alkaloids extraction?
To adjust the pH for better solubility
What distinguishes alkaloidal salts from free alkaloids in terms of extraction?
Alkaloidal salts remain behind in organic liquid, free alkaloids are present in aqueous liquid
Why is it necessary to shake the concentrated organic liquid with aqueous acid after alkaloids extraction?
To separate free alkaloids from impurities
What is the role of chloroform or other organic solvents in Method B of alkaloids extraction?
To extract pigments and unwanted materials
What is the primary reason for using ether or petroleum spirit in alkaloids extraction?
To dissolve alkaloid salts
What differentiates Method A from Method B of alkaloids extraction regarding the type of substances used for extraction?
Method A uses ammonia, Method B uses dilute acid
What is the purpose of adding excess alkalis like sodium bicarbonate in Method B of alkaloids extraction?
To precipitate the alkaloids
Why are most alkaloids considered chiral molecules?
Because they have asymmetric carbon atoms
What distinguishes alkaloidal salts from free alkaloids in terms of extraction?
Solubility in aqueous liquids
How do quaternary ammonium compounds like tubocurarine chloride or muscarine chloride differ from typical alkaloids in terms of chemical properties?
They are insensitive to pH changes
What is a common property of alkaloids as described in the text?
Nitrogen content in heterocyclic rings
What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?
Free bases are more soluble in aqueous liquids
How many nitrogen atoms can alkaloids like ergotamine contain?
$2$
What distinguishes protoalkaloids from true alkaloids based on the text?
Their biosynthetic origin
Which amino acid does not have its COOH & NH2 groups on the same carbon atom?
Tyrosine
Which term describes alkaloids that contain nitrogen in heterocyclic ring systems?
True alkaloids
What type of compounds are quaternary ammonium compounds such as tubocurarine chloride or muscarine chloride?
Pseudoalkaloids
What distinguishes reddish-brown alkaloids when extracted using Wagner's and Dragendorff's reagents?
The color of precipitates produced
Test your knowledge on the chemical properties of alkaloids, compounds that are basic and resemble ammonia. Explore how alkaloids vary in basicity depending on their structure and functional groups. Learn about the conversion of alkaloids into salts by aqueous mineral acids.
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