Pyridine Structure, Properties & Formula

Melissa Bialowas, Laura Foist, Christianlly Cena
  • Author
    Melissa Bialowas

    Melissa Bialowas has taught preschool through high school for over 20 years. She specializes in math, science, gifted and talented, and special education. She has a Master's Degree in Education from Western Governor's University and a Bachelor's Degree in Sociology from Southern Methodist University. She is a certified teacher in Texas as well as a trainer and mentor throughout the United States.

  • Instructor
    Laura Foist

    Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

  • Expert Contributor
    Christianlly Cena

    Christianlly has taught college Physics, Natural science, Earth science, and facilitated laboratory courses. He has a master's degree in Physics and is currently pursuing his doctorate degree.

Learn about pyridine. Understand the pyridine formula, its structure, its properties, such as boiling point, density, and molar mass, its reactions, and its uses. Updated: 06/09/2022

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Pyridine Formula

Pyridine is a basic organic compound with a heterocyclic structure. It is similar to benzene, as it has one methine group replaced with a nitrogen. It is a colorless liquid, known for a particularly foul odor and many hazardous properties. The compound was discovered in the late 1840s by a chemist named Thomas Anderson at the University of Edinburgh. Anderson heated animal bones to high temperatures and produced several different liquids. One of these was pyridine, which Anderson named after the Greek word for fire (pyr).

So, what is pyridine made from? The pyridine formula is {eq}C_{5}H_{5}N {/eq}. It has a ring of five carbons, five hydrogens, and one nitrogen.


The carbons form a circle with one hydrogen off of each. One pair is replaced with a nitrogen atom.

Chemical structure diagram of pyridine


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  • 0:04 Pyridine & Niacin
  • 0:42 Pyridine Formula & Structure
  • 2:17 Pyridine Physical Properties
  • 3:28 Pyridine Reactions
  • 5:11 Lesson Summary
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Pyridine Structure

Pyridine forms a ring with alternating double and single bonds. Ring compounds are very stable. It is the same structure as benzene, with one methine group replaced with a nitrogen. The properties of pyridine are different from those of benzene, however. The nitrogen makes a tertiary amine, able to have reactions including oxidation and alkylation.

The amine creates a slight dipole, or electrical pull, on the ring. This draws electrons closer to the nitrogen instead of being shared equally with all of the atoms. This makes the occurrence of an electrophilic reaction highly unlikely. Nucleophilic reactions happen so that positive charges are not placed on the nitrogen. The nitrogen makes pyridine a weak base, and it is completely miscible with water. Pyridine has a strong, putrid, fishy odor. It can be synthesized from crude coal tar, acetaldehyde, ammonia, or formaldehyde.

Pyridine Physical Properties

Like all compounds, pyridine has specific physical properties recognized by chemists. Pyridine's molar mass is approximately 79, pyridine's boiling point is 239 degrees Fahrenheit (115 degrees Celsius), and pyridine's density is {eq}0.978\frac{g}{cm^{3}} {/eq}. Here are the more important physical properties of pyridine.

  • Molecular Weight 79.10
  • Exact Mass 79.042199164
  • Color: Clear to light yellow
  • State of Matter: liquid
  • Odor: strong, nauseating
  • Density: {eq}0.978\frac{g}{cm^{3}} {/eq}
  • Flash point 68 degrees Fahrenheit, 20 degrees Celsius
  • Boiling point: 239 degrees Fahrenheit, 115 degrees Celsius
  • Melting point: -44 degrees Fahrenheit, -42 degrees Celsius
  • Solubility: miscible
  • Vapor pressure: 20 mmHg
  • Autoignition temperature: 900 degrees Fahrenheit, 482 degrees Celsius
  • pH: 8.5
  • Refractive index: 1.50920

Interestingly, because the nitrogen draws electrons toward it, there are three different chemical shifts on the hydrogens. This means that based on the position of the molecule, the H Nuclear Magnetic Radiation, better known as H-NMR, contains three signals for pyridine.

The two hydrogen atoms right next to the nitrogen are in the ortho position. They have a chemical shift of 8.6.

The two hydrogen atoms next to the ortho position are in the meta position. They have a chemical shift of 7.25.

The hydrogen atom directly across from the nitrogen in the ring is in the para position. It has a chemical shift of 7.64.

Pyridine has many hazardous properties. It is considered a highly flammable liquid and vapor. The odor is strong enough that most people will immediately detect if it is present at harmful levels. It is harmful if swallowed or if it comes into contact with skin, causing chemical burns. It can cause dizziness, headaches, lack of coordination, nausea, and loss of appetite. It causes serious eye irritation and toxicity if inhaled.

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  • Activities
  • FAQs

Pyridine: Multiple Choice Exercise

This activity will help you assess your knowledge of the structure and physical properties of pyridine.

Directions

For this activity, carefully read and select the best answer that completes each of the given statement. To do this, print or copy this page on a blank paper and circle the correct answer.

Multiple Choice


1) Niacin is a naturally-occurring vitamin present in a wide variety of food that reduces __________ build-up in the body.

A. vitamin, cholesterol

B. element, triglycerides

C. vitamin, pellagra

D. element, nitrogen


2) Pyridine is a compound having a ring of five carbon atoms and one __________ atom.

A. hydrogen

B. oxygen

C. nitrogen

D. carboxyl


3) What is special about aromatic compounds?

A. These compounds are radioactive.

B. They are stable and very unreactive.

C. Their rings break apart easily.

D. The compounds are sweet-scented.


4) A nucleophilic reaction is highlighted by an electron-receiving molecule is paired with a positively-charged molecule.

A. True

B. False


5) Carboxylic acids are electronegative and exhibit strong __________ bonding between molecules.

A. oxygen

B. nitrogen

C. carbon

D. hydrogen


6) Pyridine is a __________ liquid whose density is close to that of __________.

A. transparent, oil

B. viscous, glycerine

C. scentless, seawater

D. colorless, water


7) The following are positions where chemical shifts occur in pyridine except for __________.

A. meta position

B. para position

C. penta position

D. ortho position


8) Pyridine has the same structure as __________; only one of its carbon atoms is replaced with a __________ atom.

A. benzene, nitrogen

B. octane, hydrogen

C. fullerene, nitrogen

D. propane, nitrogen


Answer Key

  1. A
  2. C
  3. B
  4. B
  5. D
  6. D
  7. C
  8. A

Is pyridine a strong or weak base?

Pyridine is considered a weak Lewis base. It is weak because of the dipole caused by the nitrogen atom in an otherwise strong ring.

What is pyridine used for?

Pyridine is used as a solvent, in pharmaceuticals, in paints, and in textiles. It is also used in laboratories as a catalyst. It finds additional uses as a disinfectant, and it is found in some pesticides and antifreezes.

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