Nomenclature of heterocycles
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What is the primary principle of replacement nomenclature in heterocyclic compounds?

  • Replacing the carbocycle's name with the heteroatom's name
  • Using a numerical prefix to indicate the number of heteroatoms
  • Adding an elemental prefix for the heteroatom introduced to the carbocycle's name (correct)
  • Prioritizing the heteroatom according to its electronegativity

    • What is the correct order for listing heteroatoms in replacement nomenclature?

  • Alphabetical order of the heteroatom's symbol
  • Priority order based on the heteroatom's atomic number
  • Priority order based on the heteroatom's electronegativity
  • Priority order shown in table 1 (correct)

    • What is the correct name for the compound tetrahydrofuran using replacement nomenclature?

  • Dioxacyclopentane
  • Oxacyclohexane
  • Azacyclopentane
  • Oxacyclopentane (correct)

    • What is the first step in naming a heterocyclic compound using the replacement method?

    <p>Seeing the corresponding carbocyclic name</p> Signup and view all the answers

    What is the purpose of the elemental prefix in replacement nomenclature?

    <p>To indicate the type of heteroatom introduced</p> Signup and view all the answers

    What is the result of combining the carbocycle's name and the elemental prefix in replacement nomenclature?

    <p>A name composed of the corresponding carbocycle's name and the elemental prefix</p> Signup and view all the answers

    What is the main purpose of the Hantzsch-Widman nomenclature system?

    <p>To combine the prefix and suffix to determine the ring size and degree of unsaturation</p> Signup and view all the answers

    What is the correct order of components in an IUPAC name according to the Hantzsch-Widman nomenclature system?

    <p>Locants + Prefix + Suffix</p> Signup and view all the answers

    What is the role of the heteroatom in numbering a monocyclic compound?

    <p>It is always assigned position 1</p> Signup and view all the answers

    What is the purpose of the table in the Hantzsch-Widman nomenclature system?

    <p>To choose the correct prefix for the heteroatom</p> Signup and view all the answers

    How are substituents numbered in a monocyclic compound?

    <p>They are counted around the ring in a manner to take the lowest possible numbers</p> Signup and view all the answers

    What is the difference between the suffixes for nitrogen-containing and non-nitrogen-containing heterocycles?

    <p>The suffixes distinguish between nitrogen-containing and non-nitrogen-containing heterocycles</p> Signup and view all the answers

    What is the prefix for a heterocyclic ring containing nitrogen?

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

    What suffix is used for a fully saturated three-membered ring?

    <p>-idine</p> Signup and view all the answers

    What is the correct name for a heterocyclic ring containing nitrogen and oxygen, with a fully saturated four-membered ring structure?

    <p>1,2-Oxazetidine</p> Signup and view all the answers

    What is the correct order of priority for heteroatoms in a heterocyclic ring?

    <p>Oxygen, nitrogen, sulfur</p> Signup and view all the answers

    What is the correct name for a heterocyclic ring containing oxygen, sulfur, and a fully saturated five-membered ring structure?

    <p>1-Oxathiolane</p> Signup and view all the answers

    What happens when two vowels come together in a heterocyclic ring name?

    <p>The first vowel is dropped</p> Signup and view all the answers

    When two or more similar heteroatoms are present in the ring, what is used to indicate their position?

    <p>Di, tri, etc. and locants</p> Signup and view all the answers

    What is the correct order of priority when listing atom prefixes?

    <p>Oxa, aza, then others</p> Signup and view all the answers

    When combining prefixes, what should be done if two vowels come together?

    <p>Omit the vowel at the end of the first part</p> Signup and view all the answers

    How is the numbering of the ring started?

    <p>From the heteroatom of the highest priority</p> Signup and view all the answers

    What is the purpose of table 2 in the nomenclature of heterocyclic compounds?

    <p>To choose the appropriate suffix for the ring</p> Signup and view all the answers

    What is the final step in naming a heterocyclic compound?

    <p>Combining the prefix and suffix together</p> Signup and view all the answers

    What is the method of indicating the position of nitrogen or carbon atoms with extra hydrogen atoms in partially unsaturated heterocyclic compounds?

    <p>Using numbers and italic capital H followed by the name of the maximally unsaturated ring</p> Signup and view all the answers

    What is the purpose of using numbers in the nomenclature of partially unsaturated heterocyclic compounds?

    <p>To indicate the position of saturated atoms</p> Signup and view all the answers

    What is the notation used to indicate a double bond in a partially unsaturated heterocyclic compound?

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

    What is the term used to describe a partially unsaturated heterocyclic compound with two saturated atoms?

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

    What is the purpose of using special Hantzsch-Widman suffixes in the nomenclature of partially unsaturated heterocyclic compounds?

    <p>To indicate the presence of double bonds</p> Signup and view all the answers

    What is the name of the rule used for the nomenclature of partially unsaturated heterocyclic compounds?

    <p>Hantzsch-Widman rule</p> Signup and view all the answers

    Which method is used to indicate the position of saturated atoms in partially unsaturated heterocyclic compounds?

    <p>Using italic capital H</p> Signup and view all the answers

    What is the purpose of using special Hantzsch-Widman suffixes in partially unsaturated heterocyclic compounds?

    <p>To indicate the degree of unsaturation in the ring</p> Signup and view all the answers

    What is the notation used to indicate a double bond in a partially unsaturated heterocyclic compound with a four-membered ring?

    <p>∆1</p> Signup and view all the answers

    What is the correct order of components in an IUPAC name according to the Hantzsch-Widman nomenclature system?

    <p>Prefix, locant, suffix</p> Signup and view all the answers

    What is the method of indicating the position of nitrogen or carbon atoms with extra hydrogen atoms in partially unsaturated heterocyclic compounds?

    <p>Using italic capital H followed by the name of the maximally unsaturated ring</p> Signup and view all the answers

    What is the purpose of the Hantzsch-Widman nomenclature system?

    <p>To provide a systematic method for naming heterocyclic compounds</p> Signup and view all the answers

    What is the correct name for a partially unsaturated heterocyclic compound with a four-membered ring and one double bond?

    <p>2,3-Dihydro-1,3-oxathiolane</p> Signup and view all the answers

    What is the notation used to indicate the presence of two saturated atoms in a partially unsaturated heterocyclic compound?

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

    What is the method of indicating the degree of unsaturation in a partially unsaturated heterocyclic compound with a five-membered ring?

    <p>Using the symbol ∆ followed by the locant of the double bond</p> Signup and view all the answers

    What is the correct order of priority for heteroatoms in a heterocyclic ring?

    <p>O, S, N, C</p> Signup and view all the answers

    Study Notes

    Heterocyclic Ring Reactions

    • The order of aromaticity is: Benzene > Thiophene > Furan > Pyrrole
    • The order of reactivity in electrophilic substitution is: Pyrrole > Furan > Thiophene > Benzene
    • In pyrrole, the 2 & 5 (α) positions are more reactive than 3 & 4 (β) positions due to stabilization by three resonance structures

    Friedel-Crafts Alkylation

    • Furan does not undergo Friedel-Crafts alkylation due to acid sensitivity
    • Alkylation is affected by alkenes at position-2 in the presence of mild catalysts (phosphoric acid or boron trifluoride)
    • Furans substituted with electron-withdrawing substituents at position-2 undergo Friedel-Crafts alkylation at room temperature, providing a mixture of alkylfurans

    Resemblance with Phenol

    • Pyrrole reacts with CHCl3 and strong alkali to give two types of reactions: formylation at position 2 and formation of 3-chloro pyridine
    • Both reactions involve carbine generation, with the second one being a carbine insertion reaction

    Reaction of Pyrrole with Aldehydes and Ketones

    • Aldehydes and ketones condense with unsubstituted pyrrole at α position in acidic medium to give dipyrryl methane
    • The condensation may continue to give tetramer (4 pyrrole rings connected by methine bridge), known as porphyrinogens

    Reactivity Comparison with Benzene

    • The electrophilic substitution in thiophene is much easier than in benzene
    • The reactivity depends on:
      • Stabilisation energy
      • Stability of transition state
    • The lower reactivity of benzene towards electrophiles is attributed partly to the greater resonance stabilisation energy of benzene
    • The higher energy of the transition state of benzene than the structurally related transition states of five-membered heterocycles is also responsible for the lower reactivity of benzene

    Nomenclature of Heterocyclic Compounds

    • Common nomenclature: uses the corresponding carbocycle’s name and an elemental prefix for the heteroatom introduced
    • Replacement nomenclature: uses the corresponding carbocycle’s name and an elemental prefix for the heteroatom introduced
    • Hantzsch-Widman nomenclature (IUPAC): combines the appropriate prefix (or prefixes) that denotes the type and position of the heteroatom present in the ring with a suffix that determines both the ring size and the degree of unsaturation

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    Related Documents

    Organic Chemistry - Heterocyclic Compounds - Nomenclature PDF
    Organic Chemistry - Heterocyclic Compounds - Ring Reactions PDF

    Description

    Test your knowledge of nomenclature in organic chemistry, specifically focusing on heterocyclic compounds. This quiz covers different methods, including replacement nomenclature and Hantzsch-Widman nomenclature (IUPAC).

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