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Questions and Answers
According to IUPAC rules, how many nomenclatures are allowed for heterocyclic compounds?
According to IUPAC rules, how many nomenclatures are allowed for heterocyclic compounds?
- Five
- Two
- Four
- Three (correct)
Which of the following is a key component upon which the Hantzsch-Widman nomenclature is based?
Which of the following is a key component upon which the Hantzsch-Widman nomenclature is based?
- The molecular weight of the compound
- The boiling point of the compound
- The type of heteroatom (correct)
- The color of the compound
The Hantzsch-Widman nomenclature system is applicable to which type of ring systems?
The Hantzsch-Widman nomenclature system is applicable to which type of ring systems?
- Polycyclic ring systems
- Monocyclic three-to-ten-membered ring heterocycles (correct)
- All organic compounds
- Acyclic compounds
In the Hantzsch-Widman system, what does the 'prefix' indicate?
In the Hantzsch-Widman system, what does the 'prefix' indicate?
The prefixes 'oxa', 'aza', and 'thia' respectively indicate the presence of oxygen, nitrogen and sulfur atoms in a heterocyclic ring.
The prefixes 'oxa', 'aza', and 'thia' respectively indicate the presence of oxygen, nitrogen and sulfur atoms in a heterocyclic ring.
Which syllable is derived from the Latin numeral for 'tetra' and indicates a four-membered ring in nomenclature?
Which syllable is derived from the Latin numeral for 'tetra' and indicates a four-membered ring in nomenclature?
What do the endings of stems in heterocyclic nomenclature primarily indicate?
What do the endings of stems in heterocyclic nomenclature primarily indicate?
Which of the following statements about the saturated suffix in the Hantzsch-Widman system is correct?
Which of the following statements about the saturated suffix in the Hantzsch-Widman system is correct?
What is the appropriate suffix for a saturated 5-membered nitrogen heterocycle according to the nomenclature rules?
What is the appropriate suffix for a saturated 5-membered nitrogen heterocycle according to the nomenclature rules?
In naming heterocycles with substituents, the heteroatom is designated number ________.
In naming heterocycles with substituents, the heteroatom is designated number ________.
When numbering a heterocycle with substituents, which numbering scheme is preferred?
When numbering a heterocycle with substituents, which numbering scheme is preferred?
For monocyclic systems, which structural feature is considered for the parent compound?
For monocyclic systems, which structural feature is considered for the parent compound?
When a system has a lesser degree of unsaturation, what is required in its nomenclature?
When a system has a lesser degree of unsaturation, what is required in its nomenclature?
When numbering positions in a partially unsaturated heterocycle, what takes priority?
When numbering positions in a partially unsaturated heterocycle, what takes priority?
If more than one heteroatom is present in a ring which of the following represents the correct order of preference for nomenclature?
If more than one heteroatom is present in a ring which of the following represents the correct order of preference for nomenclature?
What determines how the ring is numbered in a compound if a substituent is present?
What determines how the ring is numbered in a compound if a substituent is present?
When naming fused ring systems, what does the prefix indicate?
When naming fused ring systems, what does the prefix indicate?
When a heterocyclic ring is fused to another ring, and has a saturated and an unsaturated heteroatom, where should numbering commence?
When a heterocyclic ring is fused to another ring, and has a saturated and an unsaturated heteroatom, where should numbering commence?
How can the isomerism in the position of double bonds in heterocycles be addressed?
How can the isomerism in the position of double bonds in heterocycles be addressed?
In replacement nomenclature, what does the prefix denote?
In replacement nomenclature, what does the prefix denote?
The Hantzsch-Widman nomenclature is only applicable to polycyclic heterocyclic compounds.
The Hantzsch-Widman nomenclature is only applicable to polycyclic heterocyclic compounds.
The presence of substituents does not influence how the numbering is assigned in a heterocyclic compound.
The presence of substituents does not influence how the numbering is assigned in a heterocyclic compound.
In fused ring systems, numbering must always start at the heteroatom closest to the point of fusion.
In fused ring systems, numbering must always start at the heteroatom closest to the point of fusion.
The prefixes 'bi-', 'tert-', and 'quater-' are used to indicate identical systems connected by a double bond.
The prefixes 'bi-', 'tert-', and 'quater-' are used to indicate identical systems connected by a double bond.
What is the purpose of using prefixes such as 'dihydro-' or 'tetrahydro-' in naming heterocycles?
What is the purpose of using prefixes such as 'dihydro-' or 'tetrahydro-' in naming heterocycles?
In the Hantzsch-Widman nomenclature system, what three factors are considered?
In the Hantzsch-Widman nomenclature system, what three factors are considered?
According to the information provided, what are the three most prevalent heteroatoms in heterocyclic compounds?
According to the information provided, what are the three most prevalent heteroatoms in heterocyclic compounds?
What is the name given to heterocyclic systems that are widely known, but do not follow the standard IUPAC naming conventions?
What is the name given to heterocyclic systems that are widely known, but do not follow the standard IUPAC naming conventions?
The prefixes tri-, tetra- etc. are used to indicate how many ______ ring systems are present
The prefixes tri-, tetra- etc. are used to indicate how many ______ ring systems are present
In nomenclature based on the number of double bonds, heterocyclic compounds that have the maximum number of double bonds that can be arranged in more than one way uses italic capital letters such as 1H, 2H and 3H to denote the position of the ______
In nomenclature based on the number of double bonds, heterocyclic compounds that have the maximum number of double bonds that can be arranged in more than one way uses italic capital letters such as 1H, 2H and 3H to denote the position of the ______
Match the heteroatom with its corresponding prefix in the Hantzsch-Widman nomenclature:
Match the heteroatom with its corresponding prefix in the Hantzsch-Widman nomenclature:
Match the ring size with its corresponding suffix in the Hantzsch-Widman nomenclature:
Match the ring size with its corresponding suffix in the Hantzsch-Widman nomenclature:
Based on priority of heteroatoms for numbering purposes, which of the following is the correct order from highest to lowest priority?
Based on priority of heteroatoms for numbering purposes, which of the following is the correct order from highest to lowest priority?
Which of the following is a correct example of a common name for a heterocycle?
Which of the following is a correct example of a common name for a heterocycle?
Flashcards
Hantzsch-Widman Nomenclature
Hantzsch-Widman Nomenclature
A systematic way to name heterocyclic compounds, based on heteroatom type, ring size, and saturation.
Heteroatom Prefixes
Heteroatom Prefixes
Oxa, Aza, Thia, and Phospha indicate the presence of oxygen, nitrogen, sulfur, and phosphorus in a ring, respectively.
Ring Size Suffixes
Ring Size Suffixes
Suffixes like 'ir', 'et', 'ol', 'in' indicate a ring size of 3, 4, 5, and 6 atoms, respectively.
Saturated Ring Suffixes (with Nitrogen)
Saturated Ring Suffixes (with Nitrogen)
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Naming with Prefixes/Suffixes
Naming with Prefixes/Suffixes
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Numbering Heterocycles with Substituents
Numbering Heterocycles with Substituents
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Multiple Heteroatoms
Multiple Heteroatoms
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Order of Preference
Order of Preference
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Common Names
Common Names
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Is Furan, Thiophene, or Pyrrole common names?
Is Furan, Thiophene, or Pyrrole common names?
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Identical system bond prefixes
Identical system bond prefixes
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Side Labels
Side Labels
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Naming Fused Rings
Naming Fused Rings
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Saturated atoms.
Saturated atoms.
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Extra hydrogen
Extra hydrogen
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Replacement Nomenclature
Replacement Nomenclature
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Prefix denotes heterocycles
Prefix denotes heterocycles
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Study Notes
Nomenclature of Heterocyclic Compounds
- IUPAC rules permit three nomenclature types: Hantzsch-Widman, common names, and replacement nomenclature.
Hantzsch-Widman Nomenclature
- The Hantzsch-Widman nomenclature relies on 3 characteristics: heteroatom type, ring size, and the degree of saturation
Type of Heteroatom
- Type of heteroatom is indicated by a prefix.
- O corresponds to prefix Oxa
- N corresponds to prefix Aza
- S corresponds to prefix Thia
- P corresponds to prefix Phospha
Ring Size
- Ring size is indicated by a suffix.
- Syllables are derived from Latin numerals.
- ir from tri indicates 3 atoms in the ring
- et from tetra indicates 4 atoms in the ring
- ep from hepta indicates 7 atoms in the ring
- oc from octa indicates 8 atoms in the ring
- on from nona indicates 9 atoms in the ring
- ec from deca indicates 10 atoms in the ring
Ring Saturation
- Endings indicate ring size and degree of unsaturation.
- Use appropriate prefix/prefixes combined with a stem from Table II to name heterocycles.
- The letter "a" in the prefix is omitted where necessary.
- Each suffix consists of a ring size root and an ending intended to designate the degree of unsaturation in the ring.
- The saturated suffix applies only to completely saturated ring systems.
- The unsaturated suffix applies to rings incorporating maximum non-cumulated double bonds.
- "dihydro" or "tetrahydro" prefixes are required in systems with a lesser degree of unsaturation.
Ring Saturation Examples
- Saturated 3, 4, and 5-membered nitrogen heterocycles should use "iridine", "etidine", and "olidine" suffixes, respectively.
- Oxirane is a 3-atom saturated ring, with an oxygen atom
- Thiirane is a 3-atom saturated ring, with a sulfur atom
- Aziridine is a 3-atom saturated ring with a nitrogen atom
- Oxetane is a 4-atom saturated ring, with an oxygen atom
- Thietane is a 4-atom saturated ring, with a sulfur atom
- Azetidine is a 4-atom saturated ring with a nitrogen atom
- Oxolane is a 5-atom saturated ring, with an oxygen atom
- Thiolane is a 5-atom saturated ring, with a sulfur atom
- Azolidine is a 5-atom saturated ring with a nitrogen atom
- Azinane is a 6-atom saturated ring with a nitrogen atom
- Pyridine is a 6-atom unsaturated ring with a nitrogen atom
- Azine includes N
Substituents
- In the case of substituents, the heteroatom is designated number 1.
- The substituents around the chain are numbered so as to have the lowest number for the substituents.
- The compound with the maximum number of noncumulative double bonds is regarded as the parent compound of the monocyclic systems of a given ring size.
- Oxirine is a 3-ring atom containing a double bond and an oxygen atom
- Azirine is a 3-ring atom containing a double bond and a nitrogen atom
- Azepine is a 7-ring atom containing 3 double bonds and a nitrogen atom
- Azocine is a 8-ring atom containing 4 double bonds and a nitrogen atom
Partial Saturation
- With partial saturation, use fully unsaturated name with dihydro, tetrahydro, etc.
- Numbering gives priority to saturated atoms.
- 1-Ethyl-4-methyl-4,5-dihydroazepine is a seven membered ring. Has 1 ethyl group, 1 methyl group and 1 nitrogen atom. 2 double bonds
Heteroatoms
- Two or more similar atoms contained in a ring are indicated by the prefixes ‘di-ʼ, ʻtri', etc.
- The heterocycle is named by combining prefixes with the ending in Table I with the ending order of preference: O > S > N
- In Oxaziridine, the nitrogen and oxygen are opposite each other on the 3 atom ring
- In 1,3-Thiazole (Thiazole), the nitrogen and sulfur are across from each other on the 5 atom ring
- 1,4,2 - Dithiazine includes 2 sulfur atoms and 1 nitrogen on the 6 atom ring
- 1 4-Oxazine includes 1 nitrogen and 1 oxygen on the 6 atom ring
- 3-chloro-5-methyl-1,2,4-oxadiazole includes a chlorine and methyl group includes 2 nitrogen and one oxygen
Numbering
- O > S > N for numbering
- Number the ring from the atom of preference, giving the smallest possible number to the other hetero atoms.
- Substituent position does not affect numbering of the ring.
Common Names
- Many ring systems are widely known with non-systematic or common names.
- Furan is a 5 member ring with an oxygen atom
- Thiophene is a 5 memeber ring with a sulfur atom
- Pyrrole is a 5 member ring with a nitrogen atom
- Pyridine is a 6 member ring with a nitrogen atom
Examples
- Pyridazine has 2 nitrogens
- Indole has 1 nitrogen
- Quinoline, Isoquinoline and Coumarin
Identical Systems
- Identical systems connected by a single bond are defined by the prefixes bi-, tert-, quater- etc., according to the number of systems.
- 2,2' - Bipyridine includes two 6-atom ring with a nitrogen atom on each
- 2,2': 4',3'' - Terthiophene is three 5-atom rings linked to each other. Each ring has a sulfur atom
Fused Rings
- The side of the heterocyclic ring is labeled by letters a, b, c, etc., starting from the atom numbered 1.
- The name of the heterocyclic ring is chosen as the parent compound, and the name of the fused ring is attached as a prefix. The prefix has the ending 'o', i.e., benzo, naphtho and so on
- Benzo [b] furan includes a benzine ring link to a furan ring
- Benzo [c] thiophene includes a benzine ring link to the carbon opposite the sulfur on the thiophene
- Benzo [b] pyridine includes a benzine ring linked to benzine ring linked to part of the pyridine ring
Isomers
- Always name the first element
- Always maintain numbering with heteroatoms, irrespective of where constituents are
- In a heterocyclic ring, numbering preferably commences at a saturated rather than at an unsaturated heteroatom since other things are equal.
Extra Hydrogen Handling
- Heterocycles with maximum double bonds may be arranged in more than one way.
- Adding a prefix can indicate the number of the ring atom with hydrogen using italic capital '1H''2H' '3H' etc.
- These numerals indicate the position of atoms having the extra hydrogen atom.
- The saturated position takes priority in numbering.
- In 2H-Pyran, there is two hydrogen, located on two
- In 4H-Pyran, there is two hydrogen, located on four
Replacement Nomenclature
- In replacement nomenclature, the heterocycle's name is composed of the carbocycle's name and a prefix that denotes the heteroatom.
- "aza", "oxa", and "thia" are prefixes for nitrogen, oxygen, and sulfur ring atoms, respectively.
- Heterocyclic rings are numbered so the heteroatom has the lowest possible number.
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