Stereo Chemistry Preparation and Properties
Summary of the chapter and glossary :
→ Isomerism : The compounds which have the same molecular formula but different in physical and chemical properties are called isomers and the phenomenon is called isomerism.
→ Stereoisomerism : The compounds that have the same constitution and sequence of covalent bonds but differ in relative positions of their atoms or groups in space are called stereoisomers and the phenomenon is called stereoisomerism.
→ Geometrical Isomerism : The compounds in which two different configuration of different atoms or groups attached with C = C bond in space due to restricted rotation are called geometrical isomers and this phenomenon is called geometrical isomerism.
→ Optical Isomerism : Those compounds which can rotate the plane of polarised light are called optically active compounds or optical isomers and this phenomenon is called optical isomerism.
→ Dextro rotatory : The isomer which can rotate the plane of polarised light to the right or clockwise is called dextro rotatory. It is represented by d or (+).
→ Laevo rotatory : The isomer which can rotate the plane of polarised light towards left or anticlockwise is called laevo rotatory. This is represented by I or (—).
→ Colour Dispersion : When white monochromatic light is passed through Nicol prism and distributed in mixture of seven colours are called colour dispersion.
→ Plane of Polarised Light: If the light waves pass through a polarizer which is made up of Nicol prism then only electric vibrations emerge in one plane, such beam of light is called plane of pol an sed light.
→ Specific Rotation : The optical property of the compound can be expressed by specific rotation.
where αobs observed angle of rotation
l = length of polarimeter
C = Concentration of solution
→ Plane of Symmetry : It represents the plane bisecting the molecules such that each half of the molecule is the mirror image of the other.
→ Axis of Symmetry: It represents a n-fold axis of symmetry such that when molecule possessing such an axis is rotated through an angle of 360°/n about this axis.
→ Centre of Symmetry : A molecule is said to have a centre of symmetry if any line drawn from the centre of the molecule meets identical atoms at equal distance from the centre.
→ Chiral Compounds : If the compounds in which elements of symmetry is not present, are called chiral compounds and these compounds are non-superimposable to their mirror images. This property is known as chiral.
→ Internal CompensatIon : In meso compounds, rotations are equal to upper and lower position due to plane of symmetry that’s why compounds are optically inactive and this property is called internal compensation.
→ Racernic Mixture : When equal amounts of dextrorotatory and laevo rotatory isomers are present in a compound then their type of mixture is called raemic mixture.
→ External Compensation : Racemic mixtures are optically inactive because half part rotates plane of polarised light towards right and other part rotates in opposite direction. So, they balanced each other, so it is called external compensation.
→ Optical Resolution : The process of separation of racemic mixture (dl) mixture into d and ¡ form is called optical resolution.
→ Auto Racemisation : Sorne compounds are auto racemised at room temperature, this phenomenon is called auto racemisation.
→ Chemical Racemisation : When any other chemical is mixed with d and 1 enantiomers to prepare a racemic mixture than this process is called chemical racemisation.
→ ConformatIon : The free rotation of one carbon with respect to another gives rise to various arrangements of the atoms differing in relative position of hydrogen atoms attached to these carbon atoms. These different spatial arrangements of atoms in space resulting due to free rotation around a single bond are called conformations.