Chemistry: Alkaloids Properties
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Questions and Answers

What is a common property of alkaloids?

  • They do not have definite melting points
  • They do not contain a ring structure
  • They are derived from synthetic sources only
  • They are colorless, crystalline solids (correct)

    • Why are most alkaloids considered chiral molecules?

  • To have nonsuperimposable mirror images (correct)
  • To decrease their physiological function
  • To increase their solubility in water
  • To reduce their chemical properties

    • What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?

  • Alkaloidal salts are insoluble in water but soluble in organic solvents
  • Both free bases and alkaloidal salts are insoluble in water
  • Both free bases and alkaloidal salts are soluble in organic solvents
  • Free bases are insoluble in water but soluble in organic solvents (correct)

    • How do some alkaloids deviate from the general characteristics described in the text?

    <p>They can be liquid</p> Signup and view all the answers

    Which amino acid is NOT listed as a precursor of true alkaloids in the text?

    <p>L-cysteine</p> Signup and view all the answers

    What is responsible for the basic properties of alkaloids?

    <p>Presence of an unshared pair of electrons on the nitrogen atom</p> Signup and view all the answers

    What is the typical nitrogen atom composition in alkaloids?

    <p>Usually contain one nitrogen atom</p> Signup and view all the answers

    Which alkaloid is mentioned as an example of a pseudoalkaloid in the text?

    <p>Caffeine</p> Signup and view all the answers

    In which category of alkaloids do mescaline and yohimbine belong according to the text?

    <p>Protoalkaloids</p> Signup and view all the answers

    How are alkaloids converted into salts?

    <p>By treatment with acids</p> Signup and view all the answers

    Which statement best describes the solubility of strychnine hydrochloride?

    <p>Much more soluble in water than as a base</p> Signup and view all the answers

    What distinguishes quaternary ammonium compounds from amines in terms of chemical properties?

    <p>The presence of a positive charge balanced by a negative ion</p> Signup and view all the answers

    What is the primary function of alkaloids in plants according to the text?

    <p>Protect against insects and herbivores</p> Signup and view all the answers

    Which term describes alkaloids that contain nitrogen in heterocyclic ring systems?

    <p>Heterocyclic alkaloids</p> Signup and view all the answers

    What reagent is commonly used to precipitate alkaloids from neutral or slightly acid solutions?

    <p>Mayer's reagent (potassium mercuric iodide solution)</p> Signup and view all the answers

    What color does Dragendorff's reagent produce when precipitated with alkaloids?

    <p>Yellow</p> Signup and view all the answers

    Where does the N atom in protoalkaloids like mescaline come from?

    <p>Amino acid precursors</p> Signup and view all the answers

    How many organic groups are covalently bonded to the nitrogen in quaternary ammonium compounds?

    <p>Four</p> Signup and view all the answers

    Which reagents give precipitates with proteins in the extraction of reddish-brown alkaloids?

    <p>Wagner's and Dragendorff's reagents</p> Signup and view all the answers

    How is caffeine, unlike most alkaloids, usually detected?

    <p>By mixing with potassium chlorate and hydrochloric acid</p> Signup and view all the answers

    What is the end result of exposing caffeine residue to ammonia vapor?

    <p>A purple color</p> Signup and view all the answers

    Which amino acid does not have its COOH & NH2 groups on the same carbon atom?

    <p>Phenylalanine</p> Signup and view all the answers

    What type of condensation occurs when a Schiff base reacts with a carbanion in alkaloid biosynthesis?

    <p>Mannich condensation</p> Signup and view all the answers

    Which major amino acid is involved in the biosynthesis of alkaloids and has the structure different from other amino acids?

    <p>Anthranilic acid</p> Signup and view all the answers

    What is the purpose of moistening the powdered material with alkaline substances in Method A of alkaloids extraction?

    <p>To combine with acids, tannins, and other phenolic substances</p> Signup and view all the answers

    What is the final step in Method A of alkaloids extraction after shaking the organic liquid with aqueous acid?

    <p>Separation of alkaloid salts in the aqueous liquid</p> Signup and view all the answers

    Why are organic solvents like ether or petroleum spirit used in alkaloids extraction?

    <p>To dissolve alkaloidal salts</p> Signup and view all the answers

    What role do dilute acids play in Method B of alkaloids extraction?

    <p>To help extract the pigments and unwanted materials</p> Signup and view all the answers

    Why are excess alkalis like sodium bicarbonate added in Method B of alkaloids extraction?

    <p>To precipitate the free alkaloids</p> Signup and view all the answers

    In which method of alkaloids extraction is pigment removal specifically mentioned as a step?

    <p>Method B</p> Signup and view all the answers

    What is a common property of alkaloids as described in the text?

    <p>They are generally chiral molecules</p> Signup and view all the answers

    How many nitrogen atoms can alkaloids like ergotamine contain?

    <p>Up to five</p> Signup and view all the answers

    What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?

    <p>Free bases are insoluble in water, salts are soluble</p> Signup and view all the answers

    Which statement about alkaloids is true?

    <p>Alkaloids usually contain one nitrogen atom</p> Signup and view all the answers

    How do alkalis like sodium bicarbonate play a role in Method B of alkaloids extraction?

    <p>Neutralize acidic solutions</p> Signup and view all the answers

    What is the significance of alkaloids being chiral molecules?

    <p>It results in isomers with different chemical properties</p> Signup and view all the answers

    What distinguishes protoalkaloids from true alkaloids based on the text?

    <p>Protoalkaloids have the N atom derived from an amino acid not part of the heterocyclic.</p> Signup and view all the answers

    Why are pseudoalkaloids considered different from true and protoalkaloids?

    <p>Pseudoalkaloids can be derived from non-amino acid precursors.</p> Signup and view all the answers

    What is the primary difference between typical alkaloids and atypical alkaloids according to the text?

    <p>Typical alkaloids contain nitrogen in aliphatic chains, while atypical alkaloids contain it in heterocyclic rings.</p> Signup and view all the answers

    Which function do alkaloids primarily serve in plants?

    <p>Function as protective agents against insects and herbivores</p> Signup and view all the answers

    What is a common characteristic shared by both true and pseudoalkaloids?

    <p>Both types are derived from amino acids.</p> Signup and view all the answers

    Which compounds are examples of pseudoalkaloids according to the text?

    <p>Coniine and ephedrine</p> Signup and view all the answers

    What is a distinguishing feature of caffeine, in terms of precipitation, compared to most alkaloids?

    <p>It does not precipitate like most alkaloids.</p> Signup and view all the answers

    What amino acid involved in alkaloids biosynthesis has its COOH & NH2 groups not on the same carbon atom?

    <p>Anthranilic acid</p> Signup and view all the answers

    Which reaction is NOT involved in the biosynthesis of alkaloids according to the text?

    <p>Hydrolysis</p> Signup and view all the answers

    What is the primary role of potassium chlorate in detecting caffeine?

    <p>To aid in the color change during detection.</p> Signup and view all the answers

    Which amino acid is NOT specifically mentioned as being involved in the biosynthesis of alkaloids?

    <p>Proline</p> Signup and view all the answers

    What distinguishes reddish-brown alkaloids when extracted using Wagner's and Dragendorff's reagents?

    <p>They are denatured by evaporation.</p> Signup and view all the answers

    What type of compounds are quaternary ammonium compounds such as tubocurarine chloride or muscarine chloride?

    <p>Neutral compounds</p> Signup and view all the answers

    Which reagent is NOT commonly used for precipitating alkaloids from neutral or slightly acid solutions?

    <p>Fehling's reagent</p> Signup and view all the answers

    What happens to the solubility of most alkaloids when precipitated with Mayer's reagent?

    <p>They remain insoluble</p> Signup and view all the answers

    In the context of alkaloids, why are quaternary ammonium compounds unaffected by hydroxide ions?

    <p>They have no proton to give up</p> Signup and view all the answers

    What distinguishes alkaloids like tubocurarine chloride or muscarine chloride from amines in terms of chemical properties?

    <p>Acidity</p> Signup and view all the answers

    How do quaternary ammonium compounds like tubocurarine chloride or muscarine chloride differ from typical alkaloids in terms of chemical properties?

    <p>They are less reactive</p> Signup and view all the answers

    What is the purpose of adding excess alkalis like sodium bicarbonate in Method B of alkaloids extraction?

    <p>To adjust the pH for better solubility</p> Signup and view all the answers

    What distinguishes alkaloidal salts from free alkaloids in terms of extraction?

    <p>Alkaloidal salts remain behind in organic liquid, free alkaloids are present in aqueous liquid</p> Signup and view all the answers

    Why is it necessary to shake the concentrated organic liquid with aqueous acid after alkaloids extraction?

    <p>To separate free alkaloids from impurities</p> Signup and view all the answers

    What is the role of chloroform or other organic solvents in Method B of alkaloids extraction?

    <p>To extract pigments and unwanted materials</p> Signup and view all the answers

    What is the primary reason for using ether or petroleum spirit in alkaloids extraction?

    <p>To dissolve alkaloid salts</p> Signup and view all the answers

    What differentiates Method A from Method B of alkaloids extraction regarding the type of substances used for extraction?

    <p>Method A uses ammonia, Method B uses dilute acid</p> Signup and view all the answers

    What is the purpose of adding excess alkalis like sodium bicarbonate in Method B of alkaloids extraction?

    <p>To precipitate the alkaloids</p> Signup and view all the answers

    Why are most alkaloids considered chiral molecules?

    <p>Because they have asymmetric carbon atoms</p> Signup and view all the answers

    What distinguishes alkaloidal salts from free alkaloids in terms of extraction?

    <p>Solubility in aqueous liquids</p> Signup and view all the answers

    How do quaternary ammonium compounds like tubocurarine chloride or muscarine chloride differ from typical alkaloids in terms of chemical properties?

    <p>They are insensitive to pH changes</p> Signup and view all the answers

    What is a common property of alkaloids as described in the text?

    <p>Nitrogen content in heterocyclic rings</p> Signup and view all the answers

    What distinguishes free bases of alkaloids from alkaloidal salts in terms of solubility?

    <p>Free bases are more soluble in aqueous liquids</p> Signup and view all the answers

    How many nitrogen atoms can alkaloids like ergotamine contain?

    <p>$2$</p> Signup and view all the answers

    What distinguishes protoalkaloids from true alkaloids based on the text?

    <p>Their biosynthetic origin</p> Signup and view all the answers

    Which amino acid does not have its COOH & NH2 groups on the same carbon atom?

    <p>Tyrosine</p> Signup and view all the answers

    Which term describes alkaloids that contain nitrogen in heterocyclic ring systems?

    <p>True alkaloids</p> Signup and view all the answers

    What type of compounds are quaternary ammonium compounds such as tubocurarine chloride or muscarine chloride?

    <p>Pseudoalkaloids</p> Signup and view all the answers

    What distinguishes reddish-brown alkaloids when extracted using Wagner's and Dragendorff's reagents?

    <p>The color of precipitates produced</p> Signup and view all the answers

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