Study organic chemistry

What are organic compounds?

Although organic compounds such as sugar, starch, alcohol, resins, indigo, etc had been known from the earliest times, very little progress in their chemistry until about the beginning of the eighteen century.

In 1675, Lemery published his famous Cours de Chymie, in which they divided compounds from the natural sources into three classes.
  1. Organic compounds from mineral.
  2. Organic compounds from plant namely vegetables.
  3. Organic compounds from the animal.

Carbon, hydrogen, nitrogen and phosphorus compounds

This classification was accepted very quickly, but it was Lavoisier who first showed that, in 1784, that all compounds obtained from vegetable and the animal sources always contain at least carbon and hydrogen, and frequently, nitrogen and phosphorus.

Lavoisier, in spite of showing this close relationship between vegetable and animal products, still retained L emery's classification.

Lavoisier’s analytical work, however, stimulated further research in the direction, and result in much improved in technique, due to which L emery's classification had to modify.

Lemery had based his classification on the origin of the compound, but it was not found (undoubtedly due to the improved analytical method) that in the number of cases the same compound could be obtained from both vegetable and animal sources.

Thus, no difference existed between these two classes of compounds, and it was no longer justifiable to consider them under separate headings. This lead to the reclassification of substances into two groups.

Classification of organic compounds

  1. All those which could be obtained from vegetables and animals that is the substance that was produced by living organisms were classified as organic.
  2. All those substances which were not prepared from a living organism were classified as inorganic.
Science goes day in the day with revel the information of compounds and also modification of rules and classifications also be changed. Priyam study centre discusses the all chemistry study content which helps worldwide readers who read in different schools, colleges, and universities and also the information purpose.

The empirical formula of organic compounds

The empirical formulae indicate the relative number of each kind of atom in a molecule and calculated from the percentage composition of the compound.

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 the organic compound?

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

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

Weight of oxygen in sample = 0.202 - (0.0985 + 0.0163) gm
= 0.0872 gm.

The weight of carbon, hydrogen, and oxygen by their respective atomic weights and ratio of atoms
C : H : O = (0.0985/12) : (0.0163/1) : (0.0872/16)
= 0.0082 : 0.0163 : 0.00545 = 1.50 : 2.99 : 1
= 3 : 5.98 : 2.

The empirical formula of the organic compound C₃H₆O₂.

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

Percentage of hydrogen = (0.0163/0.202) × 100
= 8.07 %.

The percentage of carbon and hydrogen is evaluated and the percentage of oxygen obtained by subtraction of thair sum 100.

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

The molecular weight of organic compounds

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

This whole number obtained from the consideration of the molecular weight of the compound. In many cases, the whole number is one.
The standard physical methods for determination of molecular weight are
  • Vapour density
  • Elevation of boiling point
  • Depression of freezing point.
These standard methods are used mainly for relatively simple molecules. There are other physical methods used for organic compounds having high molecular weight.
  • Graham's law of diffusion
  • Rate of sedimentation
  • The viscosity of the solution
  • Osmotic pressure
  • X-ray analysis
  • Mass spectrometry.

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