Stereochemistry of Organic Compound

Stereochemistry of Organic Compound

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

Stereochemistry of Organic Compound

 

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.

Stereochemistry of Organic Compound

 

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

[α ]D 

 where α = observed rotation (D = sodium lamp, λ = 589 mμ).

[α ]D

=l * d

l = length (dm)

d = concentration (g/cc)

(+)-alanine   [ α ]D = +8.5

(-)-lactic acid   [α ]D = -3.8

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