Organic compounds

Introduction to organic chemistry

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

In 1675, Lemery published his famous Cours de Chemie. In this scientific journal, they divided compounds from natural sources into three classes.

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

Organic compound with oxygen and nitrogen

This classification accepted very quickly, but it was Lavoisier who first showed in 1784.

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 Lemery’s classification.

Lavoisier’s analytical work, however, stimulated further research in the direction. The result is much improved in technique, due to which Lemery’s classification had to modify.

Lemery had based his classification on the origin of the compound. Study it 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. It was no longer justifiable to consider them under separate headings. This lead to the reclassification of substances into two groups.

Organic compounds and inorganic 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 not prepared from a living organism were classified as inorganic.

Science goes day in the day with revel the information of compounds. But the modification of rules and classifications also changed.

Online chemistry course content helps worldwide readers who read in different schools, colleges, and universities and also the information purpose.

How do you calculate the empirical formula?

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

Problem
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?

Answer
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

And weight of oxygen in sample = 0.202 – (0.0985 + 0.0163) gm
= 0.0872 gm

Thus 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)
= 3 : 5.98 : 2

The empirical formula of the organic compound C3H6O2

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 is evaluated and the percentage of oxygen obtained by subtraction of thair sum 100. Percentage of oxygen = 100 – (48.76 + 8.07)
= 43.17 %

Kinetics reaction

Law of equilibrium

Molecular weight of common 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.

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

Thus the standard physical methods for determination of molecular weight are

Vapour density Elevation of boiling point Depression of freezing point. These standard methods used mainly for relatively simple molecules. But other physical methods used for organic compounds having 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

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