PHYSICOCHEMICAL PROPERTIES
The molecular structure of the compound uniquely defines all its physical, chemical and biological
properties. It is generally recognized that physicochemical properties play an important role in
product development including studies on biological performance of drugs. A study of the physical
properties of drug molecules is a prerequisite for product preformulation, formulation development
and optimizing storage and usage conditions. It often leads to a better understanding of the
relationship between molecular structure and drug action. The most important physical properties
related to product formulation and biological performance is summarized below:
Physical properties of substances may be classified in to three types;
(i) Additive Properties: Additive properties are derived from sum of the properties of individual
properties of atoms or functional groups present within the molecule. The examples of this type
are mass or molecular weight, volume etc.
(ii) Constitutive Properties: These properties are depending on the structural arrangement of
atoms and functional groups as well as bond structure that exists within the molecules. The
examples of this type are optical activity, surface tension, viscosity etc.
(iii) Colligative Properties: Colligative properties are defined as the properties which depend
upon the total number of non-volatile solute particles present in the solution. Dilute solutions
which contain negligibly small amount of non-volatile solute exhibit colligative properties. The
examples of these properties are lowering of vapour pressure, freezing point depression, boiling
point elevation and osmotic pressure. These properties are used to determine molecular weights of
compounds.
• Refractive Index
• Optical Rotation
• Dielectric Constant
• Dipole Moment
• Dissociation Constant
1) REFRACTIVE INDEX
,Light passes more slowly through a substance than through a vacuum. As light enters a denser
substance, the advancing waves interact with the atoms in the substance at the interface and
throughout the thickness of the substance. These interactions modify the light waves by absorbing
energy, resulting in the waves being closer together by reducing the speed and shortening the
wavelength. If the light enters the denser substance at an angle, one part of the wave slows down
more quickly as it passes the interface, and this produces a bending of the wave toward the
, interface. This phenomenon is called refraction. The relative value of the effect of refraction
between two substances is given by the refractive index.
Determination :
Refractive index is determined by using instrument called refractometer. Abbes refractometer,
immersion refractometer and Pulfrich refractometer are used for this purpose. Abbes
The molecular structure of the compound uniquely defines all its physical, chemical and biological
properties. It is generally recognized that physicochemical properties play an important role in
product development including studies on biological performance of drugs. A study of the physical
properties of drug molecules is a prerequisite for product preformulation, formulation development
and optimizing storage and usage conditions. It often leads to a better understanding of the
relationship between molecular structure and drug action. The most important physical properties
related to product formulation and biological performance is summarized below:
Physical properties of substances may be classified in to three types;
(i) Additive Properties: Additive properties are derived from sum of the properties of individual
properties of atoms or functional groups present within the molecule. The examples of this type
are mass or molecular weight, volume etc.
(ii) Constitutive Properties: These properties are depending on the structural arrangement of
atoms and functional groups as well as bond structure that exists within the molecules. The
examples of this type are optical activity, surface tension, viscosity etc.
(iii) Colligative Properties: Colligative properties are defined as the properties which depend
upon the total number of non-volatile solute particles present in the solution. Dilute solutions
which contain negligibly small amount of non-volatile solute exhibit colligative properties. The
examples of these properties are lowering of vapour pressure, freezing point depression, boiling
point elevation and osmotic pressure. These properties are used to determine molecular weights of
compounds.
• Refractive Index
• Optical Rotation
• Dielectric Constant
• Dipole Moment
• Dissociation Constant
1) REFRACTIVE INDEX
,Light passes more slowly through a substance than through a vacuum. As light enters a denser
substance, the advancing waves interact with the atoms in the substance at the interface and
throughout the thickness of the substance. These interactions modify the light waves by absorbing
energy, resulting in the waves being closer together by reducing the speed and shortening the
wavelength. If the light enters the denser substance at an angle, one part of the wave slows down
more quickly as it passes the interface, and this produces a bending of the wave toward the
, interface. This phenomenon is called refraction. The relative value of the effect of refraction
between two substances is given by the refractive index.
Determination :
Refractive index is determined by using instrument called refractometer. Abbes refractometer,
immersion refractometer and Pulfrich refractometer are used for this purpose. Abbes
