12th Class Chemistry Chapter 7 Fundamental Principles of Organic Chemistry

First of all it was though that the organic compounds were synthesized in the bodies of plants and animals in the presence of vital force which is present in plants and animals as well.This concept is called vital force theory.W.F Whole discarded it by preparing urea in the laboratory.

In 1828 F.Wholer propared urea by heating ammonium xyanate in the laboratory.Urea is an organic compound present in the animal urine.

The study of the compounds containing carbon is called organic chermistry.The elements other than carbon and gydrogen present in various organic compounds are oxygen sulphur nitrogen phosphorus halogens and a few metals.

The following comounds have caron in them but they are not though to be  organic in nature.These compounds are CO.CO₂,CS₂,HCN,metal cyanides metal carbides carbonates and bicarbonates of metals.

Carbon has property to link with other atoms of carbon.This property of self-linkage is called catenation.Due to this property a separats branch of chrmistry called organic chemistry is developed.

The existance of more than one structures and having different physical and chemical properties with the same molecular formula is called isomerism.Butane has two isomers.Pentane has three and hexane has five.In this way,the number of possible molecules increases.

Organic compounds are mostly covalent in nature and insoluble in water.Their polarity is not so much pronouced so the reactions are slow.

Organic compounds are made up of such elements which have small differences of electronegativities.The bonds are very close to the covalent character and hence non-ionic.

The important solvents are ether methanol ehanol, benzene carbon tetrachloride chlorform acetone and petroleum ether.

The substances like our food clothing medicines vitamins antibiotics insecticides harmones pigments paper ink perfumes soaps detergents petroleum and plastics etc.are needed by the human beings and they are all organic substances .

Coal has plant origin and one of its fractions is coal tar.A large number of organic commpounds are present in coal tar.More than 215 organic compoounds can be extracted from four fractions of coal tar.

When coal undergoes destructive distillation between 1000- 1400 ᵒC the following five fractions are obtained.
Coal
Crude coal,       Ammonical liquor,        Coal tar ,    Coke,    Gas carbon

coal tar is one of the fractions obtained from destructive distillatin of coal.When it undergoes fractional distillation four fractions are obtained having aooroximately 215 organic compounds.
Coal Tar
Light oil,         Middle oil,                     Heavy oil            Anthracite oil.
(150-200ᵒC)      (200-250ᵒC)                (250-300ᵒC)       (300-350ᵒC)

Natural gas is consisted of 80-95% methane.It has small amounts of C₂H₆ C₃H₈ and C₄H₁₀.It also contains CO₂ H₂S and nitrogen gas.

Natural gas is used as a fuel to produce carbon black and acts as a raw material for the manfacture of urea.It is also used for power generation in cement and fertilizer industries.

Petroleum is naturally occuring brown or greenich black viscous oily liquid which is obrained from the Earth’s crust.It has biological origin and is formed due to decay and decomposition of marine animals.

When petroleum undergoes fractional distillation various fractions are natural gas petroleum ether light naphtha gasoline kerosene oil diesel oil lubrication oil and asphalt.

The industries which purify petroleum and separate different components are called oil refineries.In Pakistan we have Attack oil refinery at Rawalpindi,Pak-Arab refinery at Multan and two refineries at Karachi.

The process of decomposition of less volatile higher hydrocarbons into more volatile lower hydrocarbons with the applications of heat and catalyst is called cracking.Fractional distillation of petroleum only gives 20% gasoline.The rest of the deficiency is compensated by cracking.Approximately 50% of gasoline is now prepared by this method.

That cracking which is carried out by the application of heat and pressure is called thermal cracking.In liquid phase the temperature of 475-530ᵒC is maintained with a pressure of 7-70 atm.In vapour phase cracking the temperature is 600ᵒC and the pressure is 3.5 – 10.5 atm.

The type of cracking of hydrocarbons which is done in the presence  fo catalysts like siO₂ and AI₂O₃ is called catalytic cracking.

Higher hydrocarbons are converted to vapour and mixed with steam.This mixture is heated for a short time to about 900ᵒC and then cooled rapidly.This cracking gives us lower unsaturated hyrocarbons.

Knocking is the metallic sound during the combustion of gasoline in internal combustion engines.The gasoline having lower octane number produces knocking.

Octane number is the % age by volume of iso-octane and n-heptane which has the same knocking property as the fuel being tested under the similar experimental conditions in the special test engine.If we have greater % age of iso-octance the oxtane number is improved.

The members of homologous series contain same elements and same functional group.They have the same general formula and the members differ by – CH- units.Their properties and preparations are identical and their physical properties change gradually.

That phenomenon in which two or more than two compound have the same molecular formulae but differ at least in some physical or chemical properties is called isomerism. There are five types of structural isomerisms: i) Chain isomeris or skeletal isomerism. ii) Positional isomerism iii). Functional group isomerism. iv) Metamerism. v) Tautomerism

It has isomers which are chain isomers of each other.
CH₃.
CH₃ CH₂– CH₂– CH₃.          CH₃.CH – CH₃.
n-Butane                           2-Methyl propane

a) CH₃ – O-CH₃         CH₃– CH₂-OH are functional group.
Dimethyl ether              Ethyl alcohol    isomers of each other
O
II
b). CH₃-CH₂-CHO            CH₃– C-CH₃ are functional group
Propanal                    Propanone    isomers of each other.

Those structural in which a polyvalent atom is attached with different types of alkyl groups. CH₃ CH₂OCH₂ CH₃.and CH₃ OCH₂ CH₂  CH₃. Are metamers of each other.

The bonds are always rotating so a molecule can attain any conformation.If there is a double bond then the presence of bond does not allow the sigma bond to rotate and the rotation is hindered.In this way cis and trans geometrical isomers can exist.

It is that type of isomerism in which an atom is transferred from one part of the molecule to the other within same molecule.
O                                              OH
CH₃ –  C –  CH₃                                CH₂=C – CH₃
Acetone(keto form)                        (Enolic form)
H-atom has transferred from carbon to oxygen atom.This is called keto-enol tautomeris.

π bond are formed by parallel overlapping of p-orbitals.Two electrons give two lobs above and below the o-bond.It is weaker bond and less energy is required to break it.Its electronic cloud is more diffused as compared to electrons of o-bond.

It involves heating of coal at about 1270 K in the absence of air.It is also called destructive distillation of coal or pyrolysis.

a)Kerosene oil has B.P range of 175-325 ᵒC and its hydroxarbons vary form C₈H₁₈ .to C₁₄H₃₀.
b) Naphtha obtained from distillation of petroleum has a number of confusing names which are unscientific  and chemically erroneous.These names are petroleum ether  petroleum spirits mineral oil,mineral spirits.Their M.P may be between 50-60ᵒC and has compounds above C₂₃H₄₈.

There are two types of such compounds (i) Straight chain                (ii) Branched chain.
CH₃. CH₂– CH₂– CH₃. n-butane(st.chain)
CH₃– CH- CH₃.            Iso-butane(branched chain)
CH₃.