OPTICAL ISOMERISM

1. 2.) R/S NOMENCLATURE :- --> Absolute configuration at chiral centre. --> Not Related with optical rotation. STEPS :- # Assign Cip priority. # Least priority group must back from the observer & then go from 1-2-3 * If rotate clockwise => 'R' will assign at the chiral centre. * If rotate anticlockwise => 'S' will assign at the chiral centre.

1.1. R/S NOMENCLATURE IN WEDGE/ DASH :- # If 4th group is on dash then directly go from 1-2-3. # अगर 4th group dash पर नाही हैं तो उसे dash पर लयेगे with first exchange ऑर फिर 2nd exchange. * अगर 2nd exchange नाही करना तो 1st exchange के बाद जो भी answer अयेगा उसका उलटा बता देना.

2. SYMMETRIC OPERATION ALLOWED FOR CORRECTING FICHER PROJECTION :- 1.) Rotation of either ficher lrojection by 180° in plane is allowed. 2.) Even no.of exchange of chiral centre is allowed. (by 90°) Note:- किसी भी chiral centre पर एक valency को hold करके उसे घुमा सकते हैं Like Sir Ne notes mein Q:-2 me bataya hai Jake dekhlo.

3. Chiral Centre

3.1. 1.) Sp3 atom with bonded with 4 different Atoms / groups. 2.) A≠B≠C≠D 3.) Consider L.P as a group. 4.) Consider isotopes as different group.

4. Asymmetric Molecules:- No POS, No COS, No AOS, No AAOS

5. Symmetric Elements

5.1. 1.) Plane Of Symmetry:- An imaginary plane along which a molecule can be divided into two equal halves and both halves are mirror images of each other.

5.2. 2.) Centre of Symmetry :- Given molecule ke centre point se straight line har ek direction me pass karna aur vo straight line ke terminals identical molecules ko meet karege at equal distance from the point.

5.3. 3.) Axis Of Symmetry :- If a rotation of a molecule by (360°/n) through an imaginary line gives the molecule indistinguishable from the original, then it is said to have 'n' fold Axis Of Symmetry.

5.4. 4.) Alternating Axis Of Symmetry :- An imaginary line along which a compound is first rotated by (360°/n) and then reflected along a mirror which is perpendicular to initial line, if same appearance is obtained then the line is known as Alternating Axis Of Symmetry

6. Disymmetric Molecules :- AOS- YES , REST ALL- NO

7. Prediction Of CHIRAL AND ACHIRAL MOLECULE

7.1. 1.) अगर given molecule मे POS & COS मे से कोई एक हो या दोानो हो तो वो molecule 100% "ACHIRAL MOLECULE".

7.2. 2.) अगर POS & COS मे से कोई भी नहीं तो वो molecule 100% "CHIRAL MOLECULE"

7.3. 3.) CHIRALITY IN ALLENES :- X P \ / T1 = T2 = T3 (X≠Y , P≠Q) / \ 100% "CHIRAL" Y Q

7.4. 4.) CHIRALITY IN SPIRANES :- X /\ /\ P \ / \/ \ / / \ /\ / \ " CHIRAL " Y \/ \/ Q " SPIRANE " --> Even No of rings --> X≠Y , P≠Q

8. ENANTIOMERS :- 1. Stereoisomers which are non-superimposible mirror image. 2. Every chiral compound has one Enantiomer.

9. DIASTEREOMERS :- 1. Stereoisomers which are not mirror Image of each other and also non-superimposible. 2. Diastereomers may be chiral or achiral. 3. G.I are usually diastereomers.

10. OPTICAL ISOMERS :- Stereoisomers which have different behaviour towards PPL. (Plane Polarize Light).

11. RACEMIC MIXTURES :- 1. Equimolar mixture of enantiomeric pairs. 2. It is optically inactive.

12. MESO COMPOUND :- 1. Achiral Compounds with chiral centres. FOR STRUCTURE IS MESO :- * 2 or more chiral centres. * Structure must be divided into two equal parts after passing an imaginary line from the structure.

13. FISHER PROJECTION :-

13.1. 1. 2D representation. 2. Total no.of horizontal lines equal to total no.of chiral centre. * CRITERIA FOR CORRECT FICHER :- 1. Largest C- chain must be present at vertical line. 2. Most oxidising group must be present at top or near to top.

14. CONFIGURATION AT CHIRAL CENTRE :-

14.1. 1.) D/L NOMENCLATURE:- [ NOTE:- Not related with d & l.] STEPS :- # Compound must be in correct ficher projection. # If -OH / -NH2 / (heteroatoms) present at right side it is assign as " D-". # If ----------||----------- present at left side it is assign as "L-".

14.1.1. LIMITATIONS :- # D/L not used in symmetrical compounds. # In projection , R--> alkyl :- No heteroatom ( D/L not applicable)

14.1.2. ERYTHO AND THERO :- --> Used in compound containing two chiral centres. --> Both Chiral centre must be unidentical. # ERYTHO :- Similar groups (heteroatom) must be present on same side at unidentical chiral centre. # THREO :- Similar groups (heteroatom) must be present on opposite side at unidentical chiral centre. * If FICHER PROJECTION is given it must be Correct . √

15. STEREOGENIC UNIT :- It is a system across which any type of stereoisomerism is possible. # INCLUDES :- 1. G.I across double bond. 2. All chiral centres ( except N, C^- ) 3. Allene G.I 4. Allene ( chiral ) 5. Biphenyl ( chiral ) 6. Spirane ( chiral ) 7. Spirane ( G.I ) 8. Hemispirane NOTE :- If you find chiral centre in ring donot Include ring G.I

16. CALCULATION OF TOTAL NUMBER OF STEREOISOMERS

16.1. CHECK WHETHER THE GIVEN MOLECULE IS DIVISIBLE BY A LINE INTO TWO STRUCTURALLY EQUIVALENT HALVES OR NOT.

16.1.1. -------------------------"YES"-------------------------- # EVEN :- 1.)Total no.of optically active compounds, a = 2^ n-1 2.) Total no.of MESO compound (M = 2^ n/2-1) 3. Total no.of stereoisomers = a+M # ODD :- 1.) a = (2^ (n-1)) - (2^ (n-1/2)) 2.). M = 2^ (n-1/2) 3.) Total = a+M

16.1.2. # ODD:- 1.) a = 2^n 2.) M = 0 3.) TOTAL = a+M