Element Elements and Compounds Fundamental Concepts in Organic Reaction Mechanism Structure of Atom Compounds A compound is a substance composed of two.

ElementElements and Compounds Fundamental Concepts in Organic Reaction MechanismStructure of Atom

Compounds

A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.

Water, sugar, salt, carbon dioxide, methane etc are the examples of compounds.

Basic Principles of Organic Chemistry

Objectives:

Electronic displacement in covalent bond.

Fission of covalent bond.

Carbocation and carbanion.

ElementElements and Compounds Fundamental Concepts in Organic Reaction MechanismStructure of Atom

Compounds



Basic Principles of Organic Chemistry

Electronic Displacement in Covalent Bond

Inductive effect

Four types of electronic displacement is found in mechanism of organic reactions:

Electromeric effect

Resonance or Mesomeric effect

Hyperconjugation

ElementElements and Compounds Extraction of SulphurNon-metals

Compounds



Mineral Coal and Mineral Oil PetroleumThe s-Block Elements Diagonal Relationship and

IrregularityLithium and SodiumCompounds of CalciumBasic Principles of Organic

Chemistry Homologus SeriesFundamental Concepts in Organic Reaction Mechanism

Inductive effect

Inductive effect may be defined as the permanent displacement of electrons forming a covalent bond towards the more electronegative element or group.The inductive effect is represented by the symbol, the arrow pointing towards the more electronegative element or group of elements.


Compounds



Mineral Coal and Mineral Oil PetroleumStructure of AtomThe s-Block Elements Lithium and SodiumCompounds of Calcium

Basic Principles of Organic Chemistry Homologus SeriesFundamental Concepts in Organic Reaction

Mechanism

Any atom or group, if attracts electrons more strongly than hydrogen, it is said to have a -I effect (electron-attracting or electron-withdrawing) while if atom or group attracts electrons less strongly than hydrogen it is said to have +I effect (electron repelling or electron-releasing).

Inductive effect


Compounds




Mechanism

Electromeric effect

Electromeric effect refers to a molecular polarizability effect occurring by an intramolecular electron displacement characterized by the substitution of one electron pair for another within the same atomic octet of electrons.

Negative electromeric effect (-E effect)

Positive electromeric effect (+E effect)


Compounds




Mechanism

Electromeric effect


Compounds




Mechanism


The electron withdrawing or releasing effect attributed to a substituent through delocalization of p or π electrons, which can be visualized by drawing various canonical forms, is known as mesomeric effect or resonance effect.

Resonance effect is shown by a symbol ↔.

Two resonance structures of Benzene


Compounds




Mechanism



Compounds




Mechanism

Hyperconjugation

Hyperconjugation is the interaction of the electrons in a sigma bond (usually C–H or C–C) with an adjacent empty (or partially filled) non-bonding p-orbital, antibonding π orbital, or filled π orbital, to give an extended molecular orbital that increases the stability of the system.

Only electrons in bonds that are β to the positively charged carbon can stabilize a carbocation by hyperconjugation.


Compounds




Mechanism

Hyperconjugation


Compounds




Mechanism

Fission of Covalent BondBreaking of covalent bond of the compound is known as bond fission. A bond can be broken in two ways.

Fission of Covalent BondHomolytic

FissionHeterolytic

Fission


Compounds




Mechanism

Homolytic Fission or Homolysis

The covalent bond is broken in such a way that each resulting species get its own electron. This leads to the formation of the odd electron species called free radicals.

The free radicals are highly reactive species and have a short life.


Compounds




Mechanism

Heterolytic Fission or Heterolysis

The covalent bond is broken in such a way that one species (less electronegative) is deprived of its own electron, while other species gains both the electrons. Thus, the formation of opposite charged species takes place.

Incase of organic compounds, if positive charge is present on the carbon, then cation is termed as carbocation. If negative charge is present on the carbon, then anion is termed as carbanion.


Compounds




Mechanism

Carbocation or Carbonium ion

A species in which a carbon atom has only six electrons in its valence shell and bears positive charge is called a carbocation.

Carbocations are classified as 1°, 2°, or 3° depending on the number of carbons bonded to the carbon bearing the positive charge.


Compounds




Mechanism


Bond angles about a positively charged carbon are approximately 120°.

Carbon uses sp2 hybrid orbitals to form sigma bonds to the three attached groups.

The unhybridized 2p orbital lies perpendicular to the sigma bond framework and contains no electrons.


Compounds




Mechanism


Methyl and 1° carbocations are so unstable that they are never observed in solution.


Compounds




Mechanism


The relative stability of carbocations can be explained using the fact that alkyl groups bonded to the positively charged carbon are electron releasing and thereby delocalize the positive charge of the cation.The electron-releasing ability of alkyl groups is accounted by (1) the inductive effect, and (2) hyperconjugation


Compounds




Mechanism

Carbanion

A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons.

When a negatively charged carbon atom is directly attached to one , two or three alkyl groups then these are called primary (1°), secondary (2°) and tertiary (3°) carbanions respectively.


Compounds




Mechanism

Carbanion

Carbanions are trivalent with sp3 hybridization. The lone pare of electrons occupies one of the sp3 orbitals. The geometery is thus tetrahedral. The tetrahedron can undergoinversion or retain its stereochemistry depending on the attached substitutents.


Compounds




Mechanism

Carbanion

Alkyl groups has electron releasing tendency (due to +I effect), and therefore, increases the electron density on the negatively charged carbon atom and hence stability decreases.

More the number of alkyl groups attached to the negatively charged carbon atom greater will be the electron density on the carbon atom and lower will be its stability.

Element Elements and Compounds Fundamental Concepts in Organic Reaction Mechanism Structure of Atom Compounds A compound is a substance composed of two.

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