Preliminary ideas about reaction and Fundamental principles

Preliminary ideas about reaction and Fundamental principles

Bond fission

The process of breaking of the bond is called bond fission. It is of two types :

1. Homolytic bond fission: In this process, each atom acquires one of the bonding electron i.e. equal distributions of the electron between two atoms. Homolytic bond fission forms free electrons.

$$Cl_2\longrightarrow Cl^⋅+Cl^⋅$$

2. Heterolytic bond fission: In this process, one of the atoms acquires both of electrons bonding i.e. unequal distribution of electron takes place between two atoms. Heterolytic bond fission gives rise to electrophile and nucleophile.

$$CH_3-{Cl}\longrightarrow{CH^{+}_{3}}+{Cl}^{-}$$

• Electrophile: Electrophiles are electron deficient atom or group of the atom which attacks electron rich center. Electrophiles are electron loving species. Electrophiles are formed by heterolytic bond fission. It is indicated by E⁺. It may be positive species or neutral species or neutral molecule with electron deficient center.

Types

• Neutral electrophile: AlCl₃, BF₃, SO₂
• Positively charged ions: H⁺, CH₃⁺, No₂

• Nucleophile: Atoms or group of atoms which are able to be attracted towards electron deficient centre are called nucleophiles.

Free radicals

The atom or group having an odd number of the electron is called free radical. They are formed by homolytic bond fission.

$$Cl_2\longrightarrow Cl^⋅+Cl^⋅$$

Inductive effect

When a covalent bond is formed between two electronegative atoms, the electrons slightly shift towards more electronegative atom and bear a partial negative charge and from which the electron shifts bears partial positive charge. As a result, the polarity is produced in a molecule. So, the permanent polarity is produced in a molecule due to the different electronegativity of covalently bonded atoms called inductive effect. It is also known as field effect. It is the permanent shifting of electron pair of covalent bond towards more electronegative atom. It is denoted by (I).

The inductive effect is shown by pointing in the direction of electron displaced.

Types

• + I effect:Atom or group of the atom which donates electron towards carbon atom are said to have + I effect. Such groups are called electron donating or electron releasing group.

• – I effect: Atoms or group of the atom which withdraws electron from carbon atom are said to have – I effect. Such groups are called electron withdrawing or an electron-attracting group.

Fundamental principle

Organic chemistry and Organic Compound:

The branch of chemistry which deals about hydrocarbon and their derivative is called organic chemistry. The organic compound is the compound of hydrocarbon and their derivative in which carbon is covalently bonded.

Vital force theory

In earlier development of chemistry, compounds were classified into two types:

• Inorganic compound: compounds derived from non-living things are termed as the inorganic compound.
• Organic compound: compounds derived from living things are termed as the organic compound.

Chemist tried to synthesize organic compound in the lab but they failed. Their failure led them to believe that organic compound could be prepared within the living organism and couldn’t be synthesized in a lab like inorganic compounds. Berzelius in 1815, purposed that organic compound could only be prepared by some mysterious force existing in living organism. This force was called vital force and theory was called vital force theory.

Limitation of vital force theory

In 1825, German scientist Friedrick Wohler accidently prepared Urea heating inorganic compounds ammonium sulphate and potassium cyanide.

$$ (NH_4) _2SO_4+KCNO\longrightarrow 2NH_4CNO$$

$$NH_4CNO\longrightarrow NH_2-CO-NH_2$$

After synthesis of urea numerous organic compound like acetic acid, methane, formic acid was synthesized in lab i.e. no vital force is essential and thus in 1850 vital force theory was rejected.

Classification of organic compound

Organic compound is classified into two classes:

• Open chain compound: the organic compound which possesses the open chain of carbon atoms are called open chain compound. They are classified into two types:

1. Saturated hydrocarbon: Hydrocarbons which consists single bond between carbon atoms are called saturated hydrocarbons. E.g. methane (CH₄), ethane (C₂H₆) etc.
2. Unsaturated hydrocarbon: Hydrocarbons which consists double bond and the triple bond between carbon atoms are called unsaturated hydrocarbons. They are two types:
3. Alkene: Hydrocarbons containing the double bond between carbon atoms are called alkene. E.g. ethane (CH₂ = CH₂), propene (CH₂ = CH – CH₃) etc.
4. Alkyne: Hydrocarbons containing the triple bond between carbon atoms are called alkyne. E.g. ethyne (CH CH)

• Closed chain compound or Ring compound: the organic compound which contains a ring of carbon atoms are known as cyclic or ring compound. They are two types:

Homocyclic compound: Cyclic compound made up of carbon and hydrogen only are called the homocyclic compound. They are further classified into two types:

a. Alicyclic compound: the cyclic compound which resembles aliphatic hydrocarbon in most of their properties are called the alicyclic compound. E.g.

1. 

2. Aromatic compound: The cyclic hydrocarbon which has alternate carbon – carbon single bond and carbon − carbon double bond and similar to the benzene ring is known as aromatic compound. E.g.

   

   ,

   

3. Heterocyclic compound: The cyclic compounds which are composed of the carbon atom as well as other elements like CO, N, S etc. are known as the heterocyclic compound. E.g. oxirane pyridine

Functional group

An organic compound contains two parts i.e. hydrocarbon part (non – reacting part) and functional group (reacting part). All the compounds having the same functional group show similar chemical behavior.

Importance of functional group

• It is the basis of nomenclature.
• The functional group helps to classify organic compound in different classes or families.
• It is the site of chemical reactivity in a molecule.

Reference

Pulse, Tracy. Introduction to chemistry. u.s.a: flex book, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. Kathmandu: Vidhyarthi Pustak Bhandar, 2012.