A first-order reaction can be defined as a chemical reaction in which the reaction rate is linearly dependent on the concentration of only one reactant. A second kind of second-order reaction has a reaction rate that is proportional to the product of the concentrations of two reactants

1. FIRST ORDER AND SECOND
ORDER KINETICS
Md Altamash Ahmad
1850951001
Pharm. D 1st year

2. NUCLEOPHILE
• Nucleophile is a chemical species that donates an electron pair
to an electrophile to form a chemical bond in relation to a
reaction.
• All molecules or ions with a free pair of electrons or at least one
pi bond can act as nucleophiles.
• Because nucleophiles donate electrons, they are by definition
Lewis bases.

3. LEAVING GROUP
• A leaving group, is an atom (or a group of atoms) that is displaced as
stable species taking with it the bonding electrons.
• Typically the leaving group is an anion (e.g. Cl-) or a neutral molecule
(e.g. H2O).
• Good leaving groups are weak bases.
• Weak bases have strong conjugate acids.
• The best leaving groups "want" electrons. They don't want to share
them with other atoms.

4. FIRST ORDER REACTION
KINETICS
• A first order reaction depends on the concentration of only one
reactant.
• Like Sn¹ reaction ( substitution nucleophilic unimolecular)
• An Sn¹ reaction proceeds in two steps. The first step is the rate
determining step & form a carbocation intermediate. Its slow
step reaction.
• In the second step (fast step) ,the intermediate carbocation is
attacked by the nucleophile to give the final product.

5. SN1 REACTION

6. SECOND ORDER REACTION KINETICS
• Rate depends on the product of two concentration terms
• When you have two components reacting with each other or one
component reacting with itself
• E.g. –
2HI  H2 + I2 , here the reaction is not simply a matter of an
HI molecule falling apart, but relies on the collision of two HI
molecules.
• The rate of reaction from the law of mass action is given by-
Rate = k[HI][HI] = k[HI]2

7. SN2 REACTION AND MECHANISM
• The SN2 reaction(also known as bimolecular nucleophilic substitution) is a
type of nucleophilic substitution, where a lone pair from a nucleophile attacks
an electron deficient electrophilic centre and bonds to it, expelling another
group called a leaving group.
• SN2 process proceeds in one step via a transition state.
• The rate of reaction is proportional to both the substrate and nucleophile
concentration.
Rate = k[RX][nu-]

8. MECHANISM OF SN2 REACTION
• In SN2 process there is attack by the nucleophile from the opposite
side of the carbon atom of substrate bearing the leaving group, such
that C-X bond of the substrate breaks only as the new C-Nu bond of
the product is forming
• Therefore, in transition state, the nucleophile-carbon bond is partially
formed and the C-X bond is partially broken.
• The approach of the nucleophile from the side of the molecule
bearing the leaving group is unfavourable due to electrostatic
repulsion and also due to steric hindrance.

11. STEREOCHEMISTRY
• The branch of chemistry that studies the properties of
stereoisomers
Stereoisomers :
• Isomers that have same formula and connectivity but differ in
the position of the atoms in space
• Isomers that differ only in the position of atoms in space, and
that cannot be interconverted by rotation around a single
bond.
Stereocenter : A carbon atom bearing 4 different atoms or
group of atoms.

14. • Optically Active: the ability of some compounds to rotate
plane polarized light.
• Chiral: any molecule that is non superimposable with its
mirror image (i.e. A and B are chiral).
• Achiral: any molecule that is not chiral.
• Racemic mixture: a 1:1 (equimolar) mixture of two
enantiomers

15. • Enantiomers: stereoisomers that are non superimposable mirror
images.
• Distereomers : stereoisomers that are not mirror images.

16. • Meso compound :
A compound with at least 2 Stereocenter that is achiral due to the
presence of a plane of symmetry

17. • Cis and trans
• R and S

18. • E and Z

19. PHASE TRANSFER CATALYSIS
• Phase transfer catalysis (PTC) uses catalytic amounts of phase
transfer agents which facilitate interphase transfer of species,
making reactions between reagents in two immiscible phases
possible.
• PTC is used widely in the synthesis of various organic
chemicals in both liquid-liquid and solid-liquid systems.

21. ROLE OF SOLVENTS
1. Solvents need to get everything into solution - both the
substrate (that which is undergoing the reaction) and the
nucleophile (that which is reacting with the substrate to form
product).
2. It is best if the solvent is not reactive with either the substrate
or nucleophile.
3. SN2 reactions uses Polar Aprotic Solvents like DMSO, DMF,
tetrahydrofuran
4. SN1 reactions uses Polar Protic Solvents like Ethanol, water, acids