Six-Membered Ring Quiz and Flashcards

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Questions and Answers

What is the bond angle in pyridine?

90 degrees

120 degrees (correct)

135 degrees

105 degrees

How many carbon-nitrogen bonds are there in pyridine?

Two (correct)

Four

Three

One

What type of substitution does pyridine undergo?

Addition

Radical

Electrophilic (correct)

Nucleophilic

What is the resonance energy of pyridine?

23 kcal/mole Signup and view all the answers

How is the nitrogen in pyridine bonded to other ring members?

Using sp2 orbitals Signup and view all the answers

What does the third sp2 orbital of nitrogen contain in pyridine?

Pair of electrons available for sharing with acids Signup and view all the answers

Why is pyridine a much stronger base than pyrrole?

Presence of two unshared electrons in the sp2 orbital of nitrogen Signup and view all the answers

What is a significant difference between the reactivity of the ring in pyridine and pyrrole?

The presence of nitrogen atom in the ring Signup and view all the answers

What is the source of pyridine compounds mentioned in the text?

Coal tar Signup and view all the answers

What is the significance of the 3-isomer of pyridinecarboxylic acids mentioned?

It has vitamin properties Signup and view all the answers

Why has there been an increase in the development of syntheses involving ring closure for pyridine derivatives?

Due to increasing demand for pyridine derivatives Signup and view all the answers

What happens when the picolines are oxidized according to the text?

They yield pyridinecarboxylic acids Signup and view all the answers

What is the electronic configuration of the nitrogen atom in pyridine?

It contains a pair of electrons in the third sp2 orbital. Signup and view all the answers

What type of bond angle does pyridine have?

120 degrees Signup and view all the answers

How many carbon-carbon bonds are there in pyridine?

Four Signup and view all the answers

What does the heat of combustion of pyridine indicate?

Its resonance energy Signup and view all the answers

How is pyridine classified based on its properties?

As aromatic Signup and view all the answers

What makes pyridine resist addition reactions?

Its flat structure Signup and view all the answers

Which statement about the reactivity of pyridine is correct?

The reactivity of pyridine is influenced by the lone pair of electrons on the nitrogen atom, making it a stronger base than pyrrole. Signup and view all the answers

Which statement about the synthesis of pyridine derivatives is correct?

The increasing demand for certain pyridine derivatives has led to the development of syntheses involving ring closure. Signup and view all the answers

What is the significance of the 4-isomer of pyridinecarboxylic acids mentioned in the text?

It has been used in the treatment of tuberculosis in the form of its hydrazide. Signup and view all the answers

Which statement about the electronic configuration of pyridine is correct?

The nitrogen atom in pyridine has one electron in each p orbital and two electrons in the sp$^2$ orbital. Signup and view all the answers

Which statement about the sources of pyridine compounds is correct?

Pyridine compounds are found exclusively in coal tar. Signup and view all the answers

Which statement about the picolines mentioned in the text is correct?

Picolines are monomethyl derivatives of pyridine found in coal tar. Signup and view all the answers

Study Notes

Structure of Pyridine

Pyridine is classified as aromatic on the basis of its properties.
It is flat, with bond angles of 120°.
The four carbon-carbon bonds are of the same length, and so are the two carbon-nitrogen bonds.
It resists addition and undergoes electrophilic substitution.
Its heat of combustion indicates a resonance energy of 23 kcal/mole.
Pyridine can be considered a hybrid of the Kekul structures I and II.
The circle represents the aromatic sextet.

Electronic Configuration of Pyridine

The nitrogen atom, like each of the carbon atoms, is bonded to other members of the ring by the use of sp2 orbitals.
The nitrogen atom provides one electron for the π cloud.
The third sp2 orbital of each carbon atom is used to form a bond to hydrogen.
The third sp2 orbital of nitrogen contains a pair of electrons, which are available for sharing with acids.
This electronic configuration makes pyridine a much stronger base than pyrrole.

Pyridine Molecule

One electron is in each p orbital.
Two electrons are in the sp2 orbital of nitrogen.
The p orbitals overlap to form π clouds above and below the plane of the ring.
Two unshared electrons are still in the sp2 orbital of nitrogen.

Source of Pyridine Compounds

Pyridine is found in coal tar.
Along with it are found a number of methylpyridines, the most important of which are the monomethyl compounds, known as picolines.
Oxidation of the picolines yields the pyridinecarboxylic acids.
The 3-isomer (nicotinic acid or niacin) is a vitamin.
The 4-isomer (Isonicotinic acid) has been used, in the form of its hydrazide, in the treatment of tuberculosis.

Synthesis of Pyridine Derivatives

The increasing demand for certain pyridine derivatives has led to the development of syntheses involving ring closure.

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Description

Learn about the structure of pyridine, an important six-membered aromatic heterocycle in organic chemistry. Explore the sources of pyridine compounds and understand its classification as an aromatic compound based on its properties.