Pharmaceutical Organic Chemistry PC305: Heterocycles 1

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Questions and Answers

What is the correct name for the ring that includes one oxygen and two nitrogen atoms?

1-Oxa-2,5-diazole

2,5-Dioxiazole

1,2,5-Oxadiazole (correct)

5-Oxadiazole

Which prefix indicates the presence of two nitrogen atoms in the ring structure?

diaza (correct)

oxa

aza

thia

In the naming of heterocyclic compounds, which heteroatom takes precedence in numbering?

Carbon

Sulphur

Oxygen (correct)

Nitrogen

What is the procedure for numbering rings that contain heteroatoms?

Start with the heteroatom and give the lowest numbers to substituents. Signup and view all the answers

How is the state of hydrogenation indicated in the naming of compounds?

Through prefixes like dihydro or tetrahydro. Signup and view all the answers

What prefix is used to indicate the presence of nitrogen in a heterocyclic compound?

aza- Signup and view all the answers

In a heterocyclic compound with two oxygen atoms, which prefix should be used?

dioxa- Signup and view all the answers

What is the correct suffix for a 4-membered saturated ring that contains no nitrogen?

-etidine Signup and view all the answers

Which of the following correctly exemplifies the priority of heteroatoms in naming?

oxaza for O and N Signup and view all the answers

How should a fully saturated 5-membered aromatic ring be suffixed?

-olane Signup and view all the answers

If a ring contains one nitrogen and one sulfur, which prefix would be used in its name?

thiaza- Signup and view all the answers

What modification is made when two vowels appear together in a prefix-suffix combination?

The first vowel is eliminated. Signup and view all the answers

For a 6-membered unsaturated ring containing one nitrogen atom, which suffix is appropriate?

-irine Signup and view all the answers

What is the correct suffix for a 5-membered nitrogen-containing saturated ring?

-irane Signup and view all the answers

Which of the following compounds contains a fused heterocyclic ring?

Benzo[b]pyridine Signup and view all the answers

What is the parent component when naming a fused ring system containing a heterocyclic ring?

Heterocyclic ring Signup and view all the answers

Which of the following best describes 1H-azirine?

An unsaturated 5-membered nitrogen-containing ring Signup and view all the answers

What suffix is used for a 6-membered saturated nitrogen-containing ring?

-ine Signup and view all the answers

Which of the following does NOT represent a 5-membered nitrogen-containing structure?

Thiadiazine Signup and view all the answers

Which term refers to a compound characterized by a benzene ring plus a heterocyclic ring?

Aromatic Signup and view all the answers

What is the relationship between azolidine and pyrrolidine?

Both are saturated 5-membered nitrogen-containing rings. Signup and view all the answers

Which of the following statements about heterocyclic compounds is correct?

Almost all known drugs are derived from heterocyclic compounds. Signup and view all the answers

What is the priority order for numbering heteroatoms in fused heterocyclic compounds?

O, S, N Signup and view all the answers

When numbering heterocyclic compounds with two different heteroatoms, which of the following is true?

Numbering begins with the heteroatom that provides the lowest possible numbers for substituents. Signup and view all the answers

What does the term 'dihydro' indicate in the nomenclature of heterocyclic compounds?

The compound includes two saturated atoms. Signup and view all the answers

For unsaturated heterocyclic compounds, where does numbering begin?

At the heteroatom in the ring. Signup and view all the answers

Why might some heterocyclic compounds contain elements like selenium or phosphorus?

They can be incorporated into ring structures as heteroatoms. Signup and view all the answers

Study Notes

Pharmaceutical Organic Chemistry - PC305 Level Two, Part I: Heterocyclic Chemistry, Lec. 1

Heterocyclic compounds are cyclic molecules containing at least one atom other than carbon in the ring structure.
Common heteroatoms include nitrogen (N), oxygen (O), and sulfur (S). Other heteroatoms such as selenium (Se), phosphorus (P), silicon (Si), and boron (B) can also be incorporated.
Heterocyclic compounds can have one or more heteroatoms, which can be similar or different.
Heterocycles can be isolated or fused.
Heterocycles are a significant class of organic compounds, comprising over half of all known organic compounds.
Many drugs, vitamins, and natural products are heterocyclic.

Nomenclature of Heterocyclic Compounds

Nomenclature is based on trivial (common) names and systematic names (IUPAC/Hantzsch-Widman).
Trivial names often derive from the compound's properties or discovery.
Systematic names use prefixes specifying the heteroatom type, ring size, and degree of saturation.

Heterocyclic Compounds Containing One Heteroatom

Unsaturated heterocycles: Numbering starts at the heteroatom. Aromatic and non-aromatic types are distinguished.
Saturated heterocycles: Naming follows similar principles using prefixes like pyrrolidine.

Heterocyclic Compounds Containing Two or More Heteroatoms

Numbering starts with the prioritized heteroatom (O, S, then N) in a direction promoting the lowest possible numbers for substituents.
If multiple heteroatoms of the same type are present, numbering starts from saturated one.
If substituents are present, assign numbers to atoms bearing them and alphabetize.

Naming Heterocyclic Compounds With Saturation

Use prefixes like dihydro, trihydro, or tetrahydro to indicate the number of saturated atoms. These prefixes precede the saturated structural name

Fused Heterocyclic Compounds

Numbering starts at the nearest atom to the junction and prioritizes the heteroatom for the lowest numbers.
No numbering for contact point unless it is carbon.

Coumarin-type Compounds

Includes coumarin-2-one, chromene-4-one, and flavone.

N.B. Fused Heterocyclic compounds

Xanthine, purine, carbazole, and acridine are examples
The numbering differs from regular principles

Systematic Names (Monocyclic Systems)

The heteroatom is positioned at position 1.
Heteroatom type prefixes include oxa-, thia-, selena-, aza-, phospha-, sila-, and bora- for oxygen, sulfur, selenium, nitrogen, phosphorous, silicon, and boron, respectively.
Prefix multiplications signal two or more of the same heteroatom (e.g., dioxa, dithia, diaza).
Priority order (O > S > N) applies when multiple different heteroatoms are present.

Rule 2: Prefix and Suffix

Ring size prefixes (e.g., irine, ete, ole, etc) are followed by respective suffixes indicating saturation level (e.g., saturated or unsaturated). Perhydro is applied when fully saturated.

Example: Aziridine

3-membered ring containing nitrogen.
Combining prefix and suffix correctly eliminates vowels on the end.

Example: Oxadiazole

5-membered ring containing oxygen (O) and nitrogen(N).
Using priority of oxygen- first, locants assigned to nitrogen.

Other Heterocyclic Nomenclature (oxirane, thi-irane, azetidine, etc) and examples listed in tables.

Rule 3 - State of Hydrogenation

Use the suffix or prefixes (dihydro, tetrahydro, etc.) to indicate the degree of hydrogenation from the unsaturated parent or using ‘H’ symbol preceding numbers.

Rule 4 - Numbering Rules

Start the numbering from the heteroatom and proceed around the ring to provide the lowest possible numbers for substituents.
Oxygen (O) takes priority over sulfur (S) and sulfur (S) over nitrogen (N) for the first position.
In cases with multiple different heteroatoms, number from the heteroatom that yields the lowest numbers overall.
Arrange the lowest locant set according to the priority rule.

Examples of named compounds (including 3-methylfuran, 1,3-oxazole, 4-amino-1,3-diazine, etc.) and the correct naming procedures highlighted.

Provide naming guidelines for fused polycyclic ring systems with examples (benzo[d]thiazole, benzo[b]pyridine)

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Description

This quiz covers the fundamentals of heterocyclic chemistry as part of Pharmaceutical Organic Chemistry - PC305 Level Two. Explore the structure, nomenclature, and significance of heterocyclic compounds, which play a crucial role in the pharmaceutical industry. Understand the various heteroatoms involved and their contribution to the properties of these organic molecules.