Organic compounds definition

Definition of organic and inorganic compounds

The proper definition of organic and inorganic compounds is very complicated. But the previous definition of organic compounds is the substances produced from living organisms and inorganic compounds are the substances which were not prepared from living organisms. Although the list of organic compounds such as sugar, starch, alcohol, resins, indigo, methane, etc known from the earliest times but the formula of these compounds unknown.

But very little progress in their chemistry courses until about the beginning of the eighteen century.

In 1675, Lemery published a famous scientific journal, Cours de Chemie. They divided organic substances from natural sources into three classes.

  1. Organic compounds from mineral
  2. Compounds from plant namely vegetables
  3. Organic compounds from the animal

Chemical Baonding

Atomic Structure

Organic compounds with hydrogen, oxygen, and nitrogen

This classification accepted but very quickly Lavoisier in 1784 classified organic compounds bases on the origin.

All compounds obtained from vegetable and the animal sources always contain at least carbon and hydrogen, and frequently, nitrogen, oxygen, and phosphorus.

He showing the close relationship between vegetable and animal products.

Thus the Lavoisier’s analytical work stimulated further research in the same direction that led to modify Lemery’s classification.

Due to the improvement of the analytical techniques, some cases same compounds obtained from these two souses. This led to the reclassification of organic compounds into two classes

  1. All those which would be obtained from vegetables or animals. Thus these substances produced by living organisms.
  2. All those substances which not prepared from a living organism.

Science goes step by step with revel the new information. But the modification of rules and classifications of compounds also changed.

In 1828 Wohler converted ammonium cyanate into ures, a substance obtained from animal sources. This weekend the distinction between organic and inorganic compounds. But the previous definition of organic substances completely ended with the synthesis of acetic acid from its component elements by Kolbe in 1845.

Hence we can define organic compounds is the chemistry of carbon compounds. But this definition no longer enjoyed because it includes CO2, CO, CS2, etc.  Since these are included in inorganic chemistry. Thus organic substance is the pat of hydrocarbon.

The empirical formula of organic substances

The empirical organic formula indicates the relative number of each kind of atom in a molecule and calculated from the percentage composition of the compound.

Problem

If 0.202 gm of an organic compound gave on combustion 0.361 gm of carbon dioxide and 0.147 gm of water. What is the empirical formula of this organic compounds?

Answer

Weight of carbon = (12/44) × 0.361 gm = 0.0985 gm

Weight of the hydrogen = (2/18) × 0.147 = 0.0163 gm

Hence the weight of oxygen = 0.202 – (0.0985 + 0.0163) = 0.0872 gm

Thus the weight of carbon, hydrogen, and oxygen by their respective atomic weights and ratio of atoms are

C : H : O = (0.0985/12) : (0.0163/1) : (0.0872/16) = 3 : 5.98 : 2

Thus the of this empirical formula of the organic substance is C3H6O2

Organic Chemistry

Physical Chemistry

Empirical formula percent composition

Percentage of carbon = (0.0985/0.202) × 100
= 48.76 %

But percentage of hydrogen = (0.0163/0.202) × 100
= 8.07 %

If the percentage of carbon and hydrogen can be evaluated and the percentage of oxygen obtained by subtraction of thair sum 100.

Percentage of oxygen = 100 – (48.76 + 8.07)
= 43.17 %

Physical Chemical Properties

The molecular weight of common organic compounds

The molecular formula gives the actual number of atoms of each kind in the organic substances obtained by multiplying some whole number in the empirical formula.

But this whole number obtained from the consideration of the molecular weight. But in many cases, the whole number is one.

Thus the standard physical methods for determination of molecular weight are

  1. Vapour density
  2. The elevation of boiling point
  3. Depression of freezing point.

This list of standard methods used mainly for relatively simple organic compounds. But other physical methods used for organic substances with high molecular weight.

  1. Graham’s law of diffusion
  2. Rate of sedimentation
  3. The viscosity of the solution
  4. Osmotic pressure
  5. X-ray analysis
  6. Mass spectrometry

Gas Formula

Chemical Kinetics