Molecular models can be constructed in two main ways. Either researchers use an existing commercial force-field-based software package, or they build the molecule by assembling structural fragments stored in the molecular modeling program’s database.
Quantum mechanics is the branch of chemistry and physics that describes the behavior of matter and energy at the atomic and molecular scale.
Molecular Mechanics (MM) is a computational
method used to study molecules by applying classical physics laws instead of quantum mechanics.
OR
Molecular mechanics is a computational method that calculates molecular structure and energy using classical mechanics and force field equations without explicitly considering electrons.
Classical physics explains the motion and energy of large objects such as cars, balls, and planets.
Quantum mechanics explains the behavior of tiny particles like electrons and atoms where classical laws fail.
Why we use computational chemistry over experimental work?
We use computational chemistry to understand, predict, and design chemical systems using computers, often reducing the need for expensive and time-consuming laboratory experiments.
Computational Chemistry (Introduction)
Computational chemistry is a branch of chemistry that uses computer simulations, mathematical
models and theoretical chemistry methods to study the
structure, properties, and reactions of molecules. Instead of doing experiments
only in laboratories, scientists use computers to predict molecular behavior,
energies, and reaction mechanisms.
Or
Computational chemistry applies quantum mechanics, molecular mechanics, and statistical methods using computers to understand the chemical environment.
Stability of Alkenes
There are two factors for determining the stability of alkenes
Wittig Reaction
The Wittig Reaction is a very useful method for the synthesis of alkenes. In this reaction, aldehydes and ketones react with phosphorus ylides to form alkenes.
Cope Reaction
When
tertiary amine oxides are heated to about 150°C, they undergo thermal
elimination to form alkenes. This reaction is known as the Cope
Reaction.
Pyrolytic Eliminations
Pyrolytic
elimination reactions are those in which the elimination occurs through heating
and involves a cyclic transition state. These reactions occur
without requiring the addition of external reagents like acids or bases.
Instead, the heat provides the necessary energy to facilitate the elimination.
Preparation of Alkenes
1.
Dehydrohalogenation of alkyl halides:
Alkenes can be prepared by the elimination of hydrogen halide from an alkyl halide. Hydrogen and halogen are removed from adjacent carbon atoms, resulting in the introduction of a carbon-carbon double bond in the molecule.
Alkenes
Introduction
Alkenes
are hydrocarbons that contain at least one carbon-carbon double bond. They
follow the general formula CnH2n. A
double bond makes them unsaturated and more reactive than alkanes.
Olefins is another name for alkenes, derived from "olefiant gas" (oil-forming gas). This term historically referred to ethene () because it reacts with chlorine to form an oily liquid.
Reactions of Alkanes
1. Halogenation of Alkanes
Halogenation is a substitution reaction where hydrogen atoms in alkanes are replaced by halogens (Cl, Br). The reaction occurs via a free-radical mechanism involving initiation, propagation, and termination steps.
Preparation of Alkanes:
1. Hydrogenation
Hydrogenation involves the addition of hydrogen to
unsaturated hydrocarbons (alkenes or alkynes) in the presence of a metal
catalyst such as Ni, Pd, or Pt, under elevated temperature (250°C).
Synthesis of Tris(ethylenediamine)cobalt(III) Chloride
Objective:
To synthesize
tris(ethylenediamine)cobalt(III) chloride [Co(en)3]Cl3 ,
an octahedral coordination compound of cobalt(III) that exhibits optical
activity.
The
IUPAC (International Union of Pure and Applied Chemistry)
system provides systematic rules for naming alkanes and other organic
compounds. Here are the basic rules for naming alkanes:
Rule 1: Identify the longest continuous carbon chain in the molecule. This chain is referred to as the "parent chain," and its length determines the base name of the molecule (e.g., methane, ethane, propane, etc.).
Hydrocarbons
The branch of chemistry which
deals with the carbon and hydrogen derivatives is
called hydrocarbons.
They
can be classified into two broad categories:
Aliphatic:
These are open-chain molecules, meaning the
carbon atoms are arranged in straight or branched chains. They do not contain
aromatic rings.
Aromatic: These hydrocarbons have at least one benzene ring (a ring of six carbon atoms with alternating double and single bonds). Benzene rings provide special stability due to the delocalization of electrons.
Molecular Modeling Using Molecular Mechanics Molecular models can be constructed in two main ways. Either researchers use an existing co...
