ISOMERISM AND STERIOCHEMISTRY

“Different compound having same molecular formula are called isomers and phenomenon are called isomerism”.

Greek=isos—to same or equal,

 merisis—part or constituents.     

Isomerism is classified in to two parts-----

     1=structural isomerism

     2=stereo isomerism

structural isomerism—Same molecular formula but different structural formula.

               Ex=n-butane & iso - butane

structural isomerism are 7 types—

1=chain ,nuclear & skeleton isomerism—same molecular formula but different carbon chain.

      Ex--             n-pentane , iso pentane & neo pentane,

                          Butanol-1 2-methyl propenol-1,                                                                            Butene-1 & 2-methyl propene ,                                                                              Pentynene-1 & 3-methyl butyne-1,                                                                         Pentanol-1 & 3-methyl butanol-1,                                                                        Ethyl benzene & xylene [o ,m ,& p] .

2=position isomerism— Same molecular formula but different in position of functional group.

       Ex--              butene-1 & butene-2.

                            Butyne-1 & butyne-2.

                           1-chloropropane & 2-chloropropane.

                           1,1-di chloroethane & 1,2-di chloroethane.

                           Propanol-1 & propanol-2.

                          O-xylene , p-xylene & m-xylene.

                          Pentanone-2 & pentanope-3.

3=functional group isomerism— same molecular formula but different functional group.  Ex--

Alcohol  & ether  -- Ethyl alcohol & di methyl ether  Acid & ester       --  Acitic acid & Ethyl formate Aldehyde & ketone--   Propyl aldehyde & Acitone & Allyl alcohol                                                                                                      4=Metamerism—Same molecular formula ,same functional group but different in alkyl group joint by functional group. Ex— Amine—Methyl propyl amine & di ethyl amine & Methyl iso propyl amine , Ether—Methyl propyl ether & di ethyl ether & Methyl isopropyl ether , N-group—di methyl propyl amine,  di methyl iso propyl amine , Methyl di ethyl amine, Ketone— di methyl ketone  , Methyl propyl ketone , Methyl isopropyl ketone, 5=Cyclic or ring isomerism= Same molecular formula but different in chain open & close ring. Ex=Butene-1 & cyclo butene & methyl cyclo propane. NOTE=Ring chain isomerism are always functional isomerism. 6=Isotopic isomerism= Same molecular formula but different in isotopes of element.                    Ex=Methane-=C-12 & C-14,                           Water—H-1 & H-2,                          Formaldehyde —O-16 & O-18.         7= Tauomerism or Dynamic equilibrium=Same molecular formula but different dynamic nature of hydrogen ion or ring substituents. It also called “DESMOTROPISM”.                    Desmo = Bond & Tropos = Convertation. Tautomerism can be classified as-                                                       1-Open system tautomerism—                                                       2-Ring chain tautomerism—                                                       3-Valance tautomerism—                       NOTE—Acito acitic ester is the best example of tautomerism. & Benzophenone (C6H5—CO—C6H5) does not show tautomerism because not dynamic hydrogen .  stereo isomerism=Same constitution but different spatial arrangememt. Sterioisomers are 2 types---1-Cofigurational isomerism—                                                2-Conformational isomerism— 1-Configurational isomerism= The different spatial arrangement of atoms in a molecule which are not interconvertable without breacking of bonds & formation of bonds are called configurational isomerism. 2-Conformational isomerism=The different spatial arrengement of atoms in a molecules which are radily interconvertable by rotation single bonds are called conformational isomerism. 1-CONFIGURATIONAL ISOMEREISM=Configurational isomers are 2 types— A>   Enantiomers—Non superimposible mirror image B>   Diastereoisomers— Not mirror image. “CONFIGURATIONAL ISOMERISM “Are 2 types—                                                                      1—Optical isomerism-                                                                              2—Geometrical isomerism- 1-Optical isomerism-Same molecular formula, Same structural formula but different in configuration of valance ligands are called optical isomers & the phenomenon is called optical isomerism. NECCESSORY POINTS FOR OPTICAL ISOMERISM— A>    Plane polarized light--If Ordinary light is passed through a nicol prism ( 2-prisms of Iceland spar,CaCo3 ) ,then light vibrates only one plane is called plane polarized light & that plane is known as “plane of polarization” The whole process is called “polarization”. B> Optical activity-- BIOT(1815) passed organic solution of substances( like Glucose, Fructose, Sucrose ,Lactic acid etc.) in plane polarized light. He found a certain property to rotate with angle “This property is called optical activity.