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 is called Stereoisomers.
eg. cis-2-butene trans-2-butene
Optical activity – when a substance rotates the plane 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 optical activity of 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 * d
l = length (dm)
d = concentration (g/cc)
(+)-alanine [ α ]D = +8.5
(-)-lactic acid [α ]D = -3.8