40 Questions
What is the primary principle of replacement nomenclature in heterocyclic compounds?
Adding an elemental prefix for the heteroatom introduced to the carbocycle's name
What is the correct order for listing heteroatoms in replacement nomenclature?
Priority order shown in table 1
What is the correct name for the compound tetrahydrofuran using replacement nomenclature?
Oxacyclopentane
What is the first step in naming a heterocyclic compound using the replacement method?
Seeing the corresponding carbocyclic name
What is the purpose of the elemental prefix in replacement nomenclature?
To indicate the type of heteroatom introduced
What is the result of combining the carbocycle's name and the elemental prefix in replacement nomenclature?
A name composed of the corresponding carbocycle's name and the elemental prefix
What is the main purpose of the Hantzsch-Widman nomenclature system?
To combine the prefix and suffix to determine the ring size and degree of unsaturation
What is the correct order of components in an IUPAC name according to the Hantzsch-Widman nomenclature system?
Locants + Prefix + Suffix
What is the role of the heteroatom in numbering a monocyclic compound?
It is always assigned position 1
What is the purpose of the table in the Hantzsch-Widman nomenclature system?
To choose the correct prefix for the heteroatom
How are substituents numbered in a monocyclic compound?
They are counted around the ring in a manner to take the lowest possible numbers
What is the difference between the suffixes for nitrogen-containing and non-nitrogen-containing heterocycles?
The suffixes distinguish between nitrogen-containing and non-nitrogen-containing heterocycles
What is the prefix for a heterocyclic ring containing nitrogen?
aza
What suffix is used for a fully saturated three-membered ring?
-idine
What is the correct name for a heterocyclic ring containing nitrogen and oxygen, with a fully saturated four-membered ring structure?
1,2-Oxazetidine
What is the correct order of priority for heteroatoms in a heterocyclic ring?
Oxygen, nitrogen, sulfur
What is the correct name for a heterocyclic ring containing oxygen, sulfur, and a fully saturated five-membered ring structure?
1-Oxathiolane
What happens when two vowels come together in a heterocyclic ring name?
The first vowel is dropped
When two or more similar heteroatoms are present in the ring, what is used to indicate their position?
Di, tri, etc. and locants
What is the correct order of priority when listing atom prefixes?
Oxa, aza, then others
When combining prefixes, what should be done if two vowels come together?
Omit the vowel at the end of the first part
How is the numbering of the ring started?
From the heteroatom of the highest priority
What is the purpose of table 2 in the nomenclature of heterocyclic compounds?
To choose the appropriate suffix for the ring
What is the final step in naming a heterocyclic compound?
Combining the prefix and suffix together
What is the method of indicating the position of nitrogen or carbon atoms with extra hydrogen atoms in partially unsaturated heterocyclic compounds?
Using numbers and italic capital H followed by the name of the maximally unsaturated ring
What is the purpose of using numbers in the nomenclature of partially unsaturated heterocyclic compounds?
To indicate the position of saturated atoms
What is the notation used to indicate a double bond in a partially unsaturated heterocyclic compound?
Δx
What is the term used to describe a partially unsaturated heterocyclic compound with two saturated atoms?
Dihydro
What is the purpose of using special Hantzsch-Widman suffixes in the nomenclature of partially unsaturated heterocyclic compounds?
To indicate the presence of double bonds
What is the name of the rule used for the nomenclature of partially unsaturated heterocyclic compounds?
Hantzsch-Widman rule
Which method is used to indicate the position of saturated atoms in partially unsaturated heterocyclic compounds?
Using italic capital H
What is the purpose of using special Hantzsch-Widman suffixes in partially unsaturated heterocyclic compounds?
To indicate the degree of unsaturation in the ring
What is the notation used to indicate a double bond in a partially unsaturated heterocyclic compound with a four-membered ring?
∆1
What is the correct order of components in an IUPAC name according to the Hantzsch-Widman nomenclature system?
Prefix, locant, suffix
What is the method of indicating the position of nitrogen or carbon atoms with extra hydrogen atoms in partially unsaturated heterocyclic compounds?
Using italic capital H followed by the name of the maximally unsaturated ring
What is the purpose of the Hantzsch-Widman nomenclature system?
To provide a systematic method for naming heterocyclic compounds
What is the correct name for a partially unsaturated heterocyclic compound with a four-membered ring and one double bond?
2,3-Dihydro-1,3-oxathiolane
What is the notation used to indicate the presence of two saturated atoms in a partially unsaturated heterocyclic compound?
Dihydro
What is the method of indicating the degree of unsaturation in a partially unsaturated heterocyclic compound with a five-membered ring?
Using the symbol ∆ followed by the locant of the double bond
What is the correct order of priority for heteroatoms in a heterocyclic ring?
O, S, N, C
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
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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