Lecture 6 MUST - Isomersism, empirical and molecular formula.ppt

Lecture 5: Introduction to Organic Chemistry – A Comprehensive Guide for Undergraduate Students
This PowerPoint presentation, Lecture 5: Introduction to Organic Chemistry, is an essential resource designed for undergraduate students pursuing chemistry, biology, pharmacy, and other science-related disciplines. It provides a structured and detailed introduction to the fundamental concepts of organic chemistry, ensuring a solid foundation for further studies in the field.

Organic chemistry is a crucial branch of chemistry that focuses on the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. It plays a pivotal role in various scientific fields, including medicine, pharmaceuticals, biochemistry, environmental science, and materials science. This lecture presentation covers the core principles necessary to understand organic molecules and their transformations, making it an invaluable tool for students and educators alike.

Key Topics Covered in this Lecture:
1. Introduction to Organic Chemistry
Definition and significance of organic chemistry in the scientific world.
Historical development of the field and major contributors.
The distinction between organic and inorganic compounds.
2. Structure and Bonding in Organic Compounds
Atomic structure and electronic configuration.
Covalent bonding and hybridization (sp, sp², sp³).
Molecular orbital theory and resonance structures.
The concept of electronegativity and polarity in organic molecules.
3. Functional Groups and Their Importance
Overview of key functional groups: alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, and aromatic compounds.
How functional groups determine the chemical properties and reactivity of organic molecules.
The role of functional groups in biological and industrial applications.
4. Nomenclature of Organic Compounds
Systematic IUPAC naming conventions for aliphatic and aromatic compounds.
Common names vs. IUPAC names.
Rules for naming branched-chain hydrocarbons, cyclic compounds, and complex organic molecules.
5. Isomerism: The Different Forms of Organic Molecules
Structural isomerism: Chain, positional, and functional group isomers.
Stereoisomerism: Geometrical (cis-trans) and optical isomerism.
Chirality and enantiomers in biological systems.
6. Reaction Mechanisms in Organic Chemistry
Introduction to reaction mechanisms and their importance in predicting product formation.
Classification of organic reactions:
Substitution reactions (SN1, SN2)
Addition reactions (electrophilic and nucleophilic addition)
Elimination reactions (E1, E2 mechanisms)
Rearrangement reactions
Oxidation and reduction reactions in organic synthesis
The role of catalysts and reaction conditions in determining reaction outcomes.
7. Organic Chemistry in Everyday Life
The impact of organic chemistry on medicine and drug development.
The significance of polymers and plastics in modern mater

1. Hydrocarbons: IsomerismHydrocarbons: Isomerism
Lecturer:
Applied studies
MIT, MUST
February, 2017

2. Isomers
Isomers are molecules that have the same molecular
formula but different structural formulas
Structural isomers are also known as constitutional
isomers
Constitutional or structural isomers have their atoms
joined together in a different sequence.

3. Isomerism in Alkanes
Structural isomers are possible in all alkanes containing four or
more carbon atoms.
Isomers are deduced by drawing the different possible
arrangements of carbon atoms
Arrangements that may be interconverted by rotating the carbon
framework are not structural isomers.
 For example: the different structural isomers for butane, C
4
H
10
, a
straight chain and a branched chain isomer:
Straight- chain Branched-chain

4. Examples of Isomerism in Alkanes:
Pentane
Practice: How many isomers of hexane are there? Draw and
name them appropriately
Draw all isomers of heptane and name them using IUPAC
rules of nomenclature
pentane 2-methylbutane 2,2-dimethylpropane

5. Classes of Carbon atoms: Primary (1),
Secondary (2), Tertiary (3) and Quaternary
(4) Carbons
In straight chain alkanes the non-terminal carbon atoms
are bonded to two other carbon atoms.
In a branched alkane one or more carbons are bonded to
three or four other carbon atoms.
CH
3CC CH
3
CH
3
CH
3
H
CH
3
C bonded to three other C atoms
C bonded to four other C atoms
CH
3CC CH
3
H
H
H
H
Terminal Carbon
Terminal Carbon
non-terminal Carbon

6. 1, 2, 3 and 4 Carbon
atoms....
Primary carbon atom: A carbon atom bonded to only one other
C atom.
Secondary carbon atom: One bonded to two other C atoms.
Tertiary carbon atom: One bonded to three other C atoms.
Quaternary carbon atom: One bonded to four other C atoms.
It therefore follows that hydrogen atoms bonded to primary,
secondary and tertiary carbon atoms are referred to as primary,
secondary and tertiary hydrogen atoms, respectively

7. Isomerism in alkyl groups
Isomerism also exists in alkyl groups mainly due to:
•Branching of the chain
•Differing points of attachment to the parent chain
For example: isomers of propyl group
•The propyl group can be attached through a terminal carbon
•The propyl group can also be attached through secondary
carbon
propyl group
CH
3CH
2CH
2
isopropyl group
CH
3CHCH
3

8. Isomerism in alkyl groups: Examples of
isomerism in alkyl groups
butyl group
CH
3CH
2CH
2CH
2
isobutyl group
CH
3CHCH
2
CH
3
sec-butyl group
CH
3CH
2CH
CH
3
tert-butyl group
CH
3C
CH3
CH
3
pentyl group
CH
3CH
2CH
2CH
2CH
2
isopentyl group
CH
3CHCH
2CH
2
CH
3
neopentyl group
CH
3CCH
2
CH
3
CH
3
tert-pentyl group
CH
3CH
2C
CH
3
CH
3

9. Isomerism in Alkenes: Geometric Isomers
Alkenes and alkynes differ from alkanes in shape because of their
multiple bonds.
For example methane is tetrahedral, ethene is flat and ethyne is
linear (predicted by the VSEPR model).
Further there is no rotation around the double bonds unlike the
situation in alkanes, where free rotation around the single bond
occurs,
Consequently , Geometric Isomerism exists for alkenes
◦due to lack of free rotation around the carbon-carbon double bond
Consequently if both carbon atoms of the double bond have two
different groups attached, cis and trans isomers exist

10. Isomerism in Alkenes: Geometric Isomers
Cis: when the two substituted groups are on the same side of the
double bond
Trans: when the two substituted groups are on the opposite sides of
the double bond
The two but-2-enes are called cis–trans isomers. They have the
same formula and connections between atoms but different
structures
cis-but-2-ene
CH
3
CC
CH
3
H H
trans-but-2-ene
CH
3
C C
CH
3
H
H

11. Isomerism in Alkenes: Geometric Isomers
Cis–trans isomerism occurs in an alkene whenever each double-
bond carbon is bonded to two different substituent groups.
If one of the double-bond carbons is attached to two identical
groups, cis–trans isomerism is not possible.
Reflection: Can ethene and propene exhibit geometric Isomerism?

12. More examples of Geometric Isomers
cis-pent-2-ene
CH
3
CC
CH
2CH
3
H H
trans-pent-2-ene
CH
3
C C
CH
2CH
3
H
H