Stereochemistry of Organic Compound
Chemistry in three dimensions
Isomers – different compounds with the same molecular formula is known as the Isomers of each other.
Structural Isomers – isomers that differ in which atoms are bonded to which atoms is known as the Structural Isomers.
Stereoisomers – isomers that differ in the way the atoms are oriented in space, but not in which atoms are bonded to which atoms are called Stereoisomers.
eg. cis-2-butene trans-2-butene
Optical activity – when a substance rotates the plane polarized light the substance is said to be optically active. (1815 by Biot)
Plane polarized light – light that has been passed through a Nicol prism or other polarizing medium so that all of the vibrations are in the same plane; then the light is said to be Plane polarized light.
Polarimeter – an instrument used to measure the optical activity of a substance is known as the Polarimeter.
Dextrorotatory – when the plane of polarized light is rotated in a clockwise direction when viewed through a polarimeter is known as the Dextrorotatory.
It is denoted by (+) or (d) ∗∗∗ do not confuse with D
levorotatory – when the plane of polarized light is rotated in a counter-clockwise direction when viewed through a polarimeter.
It is denoted by (-) or (l) ∗∗∗ do not confuse with L
The angle of rotation of plane-polarized light by an optically active substance is proportional to the number of atoms of the substance in the path of the light.
Specific rotation – the angle of rotation of plane-polarized light by a 1.00 gram per cm-3 sample in a 1 dm tube. the specific rotation is measured by the following equation
where, α = observed rotation (D = sodium lamp, λ = 589 mμ).
=l x d
where, l = length (dm), d = concentration (g/cc)
(+)-alanine [ α ]D = +8.5
(-)-lactic acid [α ]D = -3.8