The document discusses hydrophobic interactions and effects. It defines hydrophobicity as molecules that do not interact well with water, such as nonpolar substances. When these molecules are introduced into water, they aggregate together to minimize contact with water molecules. This occurs because breaking hydrogen bonds between water and the hydrophobic molecules is entropically unfavorable. The hydrophobic effect is driven by this entropy change and causes nonpolar substances to cluster together in aqueous solutions.

1. GUIDED BY-
Dr. ASHISH KUMAR BHUI
PRESENTED BY-
SUBHI PATEL

2. •Introduction
•Definition
•Causes
•Thermodynamics
•Formation
•Strength
•References

3.  Hydrophobic interaction describes the relation between
water and hydrophobes.
 Hydrophobes are non polar molecule and usually have a
long chain of carbons that do not interact with water
molecule.
 The mixing of fat and water is a good example of this
interaction.

4.  The hydrophobic effect is the observed tendency of
non polar substances to aggregate in an aqueous
solution and exclude water molecules.
A droplet of water forms
a spherical shape, minimizing
contact with hydrophobic leaf.

5. The tendency of non-polar molecule in
a polar solvent (usually water) to
interact with one another is called
hydrophobic effect.
 The interaction between the non-
polar molecule are called hydrophobic
interaction.

6.  The non-polar substance like fat molecules tend
to clump up together rather than distributing itself
in a water medium, because this allow the fat
molecules to have minimal contact with water.

7.  When a hydrophobe is dropped in an aqueous
medium hydrogen bonds between water molecules
will be broken to make space for the hydrophobe.
 This considered an endothermic reaction, because
when bonds are broken heat is put into the system.
 Water molecules that are distorted by the pressure of
the hydrophobe will make a new Hydrogen bonds
and form an ice like cage structure called a clathrate
cage around the hydrophobe.

8.  This orientation makes the system more structured with an
decreases of the total entropy of the system; ΔS < 0.
 The change in enthalpy (ΔH) of the system can be positive,
negative or zero because new H-bond can partially, completely
or over compensate for the H-bond broken by the entrance of
the hydrophobe.

9.  The change in enthalpy, however is insignificant in
determining the spontaneity of reaction (mixing of
hydrophobic molecule and water) because the
change in entropy is large ΔS.
 According to Gibb’s formula,
ΔG = ΔH – TΔS ---------- ( I )
In case if ΔH is small and ΔS is more negative
then ΔG will be positive , hence hydrophobic
interaction is not spontaneous.

10.  The mixing hydrophobes and water is not
spontaneous, however, hydrophobic interaction
between hydrophobes are spontaneous.
 When hydrophobes come together and interact with
each other, enthalpy increase (ΔH is positive)
because some of hydrogen bonds that form the
clathrate cage will be broken.
 Tearing down a portion of clathrate cage will cause
the entropy to increase (ΔS is positive) since
forming it decreases the entropy.

11. According to equation ( I )
If ΔH is small positive value and ΔS is large positive
value then ΔG will be negative hence hydrophobic
interaction is spontaneous.

12. 1. TEMPRATURE- Strength of hydrophobic
interaction increases with in temperature.
2. NO. OF CARBONS IN HYDROPHOBES-
Molecules with greater number of carbon will have
the strongest hydrophobic interaction.
3. SHAPE- aliphatic organic molecules have
stronger interaction than aromatic compound.

13. Branches on a carbon chain will reduce
the hydrophobic interaction of that
molecule and linear carbon chain can
produce the largest hydrophobic
interaction.
This is because carbon branches produce
steric hindrance. So it is harder for two
hydrophobes to have very close
interactions with each other.