Organic compound notes class 11 chapter 12

 Introduction

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Organic compound

The branch of chemistry which studies organic compounds is called organic chemistry.

The classical definition of Organic compound

The organic word means ‘to live’ means a compound that is obtained from living organisms (plant and animal sources) is called an organic compound. This definition is based on vital force theory (V.F.T) which is given by Berzelius.

Vital force theory (V.F.T)

According to this theory, the organic compound is only obtained from plant and animal sources, not man-made, synthesised or prepared in the lab. But this theory was reputed by a student of Berzelius named Wohler and he prepared organic compounds in the lab.

The first organic compound which is prepared in the lab is nitrogenous fertilizer urea, which is made from the re-arrangement of ammonium cyanate NH4CNO.

NH4CNO re-arrangement NH2CONH2

Urea:- NH2CONH2

14 + 1×2+12+16+14+1×2=60

Per cent of N = 28/60×100=46.6%

The modern definition of Organic compound

An organic compound is a Compound of carbon but some Compound of carbon which is not organic compound like CO, CO2, CaCO3, NaCO3, KCN. These compounds contain carbon but not organic compounds. So, the modern definition of an Organic compound is a hydrocarbon and its derivatives.

Derivatives mean replacing Hydrogen from hydrocarbon with other elements like Nitrogen, Halogen, oxygen, Sulphur and phosphorus.

CH4   Hydrocarbon

CH3-Cl   Derivatives of hydrocarbon

Nature of carbon compound

Carbon compound is not an ionic compound. It is a covalent compound and its covalency is 4. So, it is called tetravalency.

Type of covalent bond

1. Sigma Bond

2. Pie Bond

Calculation of Sigma and pie Bond

• All single bonds are Sigma Bond.

• In multiple Bond, one is Sigma and all others are pie Bond.

The covalent compound is directional and it has definite geometry and shape which is determined with the help of Hybridisation.

Hybrid orbital=Sigma + loan pair

If the sum is 2: SP linear 180°

If the sum is 3:  SP2 trigonal plannar120°

If the sum is 4:  SP3 tetrahedral 109•4°

Example-

HCN

Sigma = 2 pie=2 loan pair=0

Hybrid orbital=Sigma + loan pair =2 + 0=2: SP

Shape=linear

Bond angle=180°

Hybrid orbital=2

Unhybrid orbital=2

Catenation property

The carbon atom has the self-linkage property means it attach to another carbon atom in a straight chain, branch chain and ring. This property of carbon is called the catenation property.

Concept of the degree of unsaturation (DU) or Hydrogen deficiency index (HDI)

DU Or HDI = Cn+1 – (H + X – N)/2

X= Halogen

N= Nitrogen

H= Hydrogen

Example

C4H4

DU= 5 – 6/2=2

Representations of an organic molecule

1. Structure formula:- When each atom represents in the form of a structure, this is called the structurel formula.

2. Condense formula:- when all hydrogen attaches to carbon written together, this representation is called condense formula, the organic compound is generally written in the form of condensed formula.

3. Bond line representation:- when carbon is denoted by Dot (.)  In zig Zag form. A single bond is denoted by a single line. The double bond is denoted by a double line. A triple bond is denoted by a triple line. The hydrogen atom is not mentioned and another atom is mentioned. This representation is called bond line representation.

4. Molecular formula:- When all carbon and hydrogen wrote together, this is called molecular formula.

To be continued…..

Upcoming topics in the next part

• 3-d representation of organic compound

• Size of hybrid orbital

• And more….

Some FAQs