Organic Chemistry

Lesson 7: Organic Chemistry

Under this topic we will look at the homologous series one after the other, I mean the alkane, alkene, alkyne and so on. One after the other, there method of production, physical and chemical properties, test and uses.

INTRODUCTION

What is organic chemistry?

This is the branch of chemistry that deals with the compound of hydrocarbons.

Types of organic compounds

There are two major types of hydrocarbon which are

1.      Aliphatic hydrocarbon: these are the hydrocarbon that are made up of straight, branched or cyclic carbon atoms.   

2.      Aromatic hydrocarbon : these are the hydrocarbon that contains ring structure of carbon with Non- localized orbital. i.e. non-localized pi bond e.g. benzene, phenol, toluene and turpentine.

Aliphatic hydrocarbon carbon grouped into:

a.       Acyclic hydrocarbon: these are hydrocarbon with straight chain e.g. ALKANE and ALKENE   

b.      Cyclic hydrocarbons: these are hydrocarbons in cyclic form. e.g. Cyclo-pentane, Cyclo-hexane. They only form ring structures with single bond.

Acyclic can be group as saturated and unsaturated hydrocarbons

a.       Saturated hydrocarbons: these are hydrocarbons with single covalent bond e.g. the ALKANE family.

b.      Unsaturated hydrocarbons: these are hydrocarbons with double or triple covalent bond. E.g. ALKENES and ALKYNES.

CHEMISTRY OF ALKANE

            Alkanes are saturated, acyclic, aliphatic hydrocarbon with the general formula CnH2n+2. Where is an integer starting from 1.the functional group of alkane is (C-C).

THE FIRST TEN MEMBER OF THE FAMILY ARE:

Number of carbon	Name	Molecular Formula
1	Methane	CH4
2	Ethane	C2H6
3	Propane	C3H8
4	Butane	C4H10
5	Pentane	C5H12
6	Hexane	C6H14
7	Heptane	C7H16
8	Octane	C8H18
9	Nonane	C9H20
10	Decane	C10H22

MOLECULAR STRUCTURE

Name	Molecular Formula	Condensed structure
Methane	CH4	CH4
Ethane	C2H6	CH3-CH3
Propane	C3H8	CH3-CH2-CH3
Butane	C4H10	CH3-CH2-CH2-CH3
Pentane	C5H12	CH3-CH2-CH2-CH2-CH3
Hexane	C6H14	CH3-CH2-CH2-CH2-CH2-CH3
Heptane	C7H16	CH3-CH2-CH2-CH2-CH2-CH2-CH3
Octane	C8H18	CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3
Nonane	C9H20	CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3
Decane	C10H22	CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

 General Laboratory preparation alkane

Alkane are generally prepared in the laboratory by heating the mixture of  Alkanoate (salt made from Alkanoic acid and sodium metal like sodiumthanoate, sodiumpropanoate, sodiumbutanoate. E.t.c.) salt with soda lime (CaHNaO₂).

GENERAL PHYSICAL PROPERTIES OF ALKANE

1.      Methane and ethane are gas at room temperature, propane and butane are liquid at room temperature while others are solid

2.      They have no action on litmus paper

3.      They are slightly soluble in water. Solubility decreases as the the number of carbon atom increases.

GENERAL CHEMICAL PROPERTIES

1.      Combustion reaction: all alkane burns in air with a blue non-luminous flame to give carbon(iv)oxide and water. E.g. CH₄ + 2O₂  → CO₂ + 2H₂O

2.      Substitution reaction: substitution reaction is a kind of chemical reaction whereby an atom or a group of atom is replace by another atom of group of atom. Alkanes can undergo substitution reaction with the halogens. And the reaction is also called halogenation. For example methane undergoes substitution reaction with chlorine to give choloro-methane in the presence of sunlight.

Chemical test for alkane

1.      All members of alkane has no effect on bromine water

2.      All members of alkane has no effect on acidified and alkalined potassium heptaoxodichromate(vi). (K₂Cr₂O₇) and potassium tetraoxomanganates (vii).(KMnO₄).

USES OF ALKANES

1.      They can be used as fuel

2.      Methane is used in the production of water gas

3.      They can be used in the production of hydrogen, alkynes, chloroform and so on.

4.      Tetrachloromethane is used as organic solvent in industries for manufacturing process.

LESSON 6: ISOMERISM

What is isomerism?

This is the occurrence of two or organic compound having the same molecular formula but different but different structural formula. E.g. C4H10 is the molecular formula of butane. But I can have two different structural formula for the same compound.

CH3-CH2-CH2-CH3 this is butane.

CH3-CH-(CH3)-CH3 this 2-methlybutane.

But compound are of the same formula (C4H10) but their structure is different. So they are isomers of each other and their existence is referred to as isomerism.

Types of isomerism

There are basically two types of isomerism which are:

1.      Structural or constitutional isomer

2.      Stereo isomers

   

1. Structural isomers: these are isomers that are differ from one another due to their due to their form of attachment. E.g. CH3CH2CH2CH3 can also be written as 

And if you look at the two structure, it is still C4H10.

Structural isomers can be further divided into four (4) which are:

a.       Branched chain isomers: they are isomers having the same number and kind of atoms but different structures due to the presence of branched chain. e.g. 2-methlypropane and butane. CH3-CH-(CH3)-CH3 and CH3-CH2-CH2-CH3, 2-methylbutane and pentane. CH3-CH-(CH3)-CH2-CH3 and CH3-CH2-CH2-CH2-CH3.

b.      Positional isomers: they are isomers with the same substituent on different carbon chain. e.g. 3-methylpentane and 2-methylpentane. CH3-CH2-CH(CH3)-CH2-CH3 and CH3-CH(CH3)-CH2-CH2-CH3

c.       Functional group isomers: the functional group isomers are different from one another as a result of placement of the functional on different carbon atom of compounds having the same number of carbon. E.g. propan-1-ol and propan-2-ol are both alcohol but the location of the hydroxyl group is on carbon 1and 2 respectively. CH2(OH)-CH2-CH3 and CH3-CH(OH)-CH3.

d.      Tautomerism: this is a state of equilibrium between two functional groups on the same compound. There are some compounds like aldehyde and ketone that when they undergo certain reaction, they bear two functional group at the same time, the equilibrium point of these functional group is called tautomerism. ENOL-KETO tautomerism. It will be discussed later under the chemistry of carbonyl compounds.

2.      Stereo isomerism or stereo isomers: this type of isomers occurs as a result of different spatial orientation of the compounds despite the fact that they are having the same molecular formula, their structure differs as a result of how the atoms are being orientated. E.g. cis and trans isomers (it will discussed below.)

There are two types of stereo isomers, which are

a.       Geometric isomers: this occurs in compounds with double bond. The double bond restricts free rotation within a molecule and fixes the positions in space of those atoms or group link to it.

The geometric isomers can generally be represented as follows.

The Cis – isomer contains like groups on the same side of the double bond while the trans – isomer has like groups on opposite sides of the double bond.  

b.      Optical isomers: these are isomers that just like mirror image of each other on a plane polarized light. E.g. see the picture below.