Stereochemistry- Notes PDF

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STEREOCHEMISTRY

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STEREOCHEMISTRY 1. General description of stereochemistry. 2. Basic terminology of stereochemistry. 3. Conventions for configurations R– S system. 4. Stereoisomers and interconversion between i) Enantiomers,

(ii) Diasteceoisomers

(iii) Homomers.

5. Representation of three Dimensional molecules and interconversion i) Fischer Profections representations. ii) Flying wedge representation iii) Sowhore representtions iv) Newmann projection representations. 6. Symmetry element 7. Stereoisomerism resulting from more than one stereogenic unit i) Threo and erythro Nomenclature. ii) Meso and d-l pair system. iii) Conventions for configuration D and L pair. 8.

Chirality i) Allenes ii) Spirans iii) Atropisomers iv) Helicity

9. Geometrical Isomerism 10. Topicity / Prochirality i) Enantiotopic. ii) Diastereotopic iii) Homotopic  Cram’s rule  Anti Cram’s rule  Prelog’s rule 11. Conformations – i) Conformation in acyclic system Ethene , n-propane, n Butane ii) Conformations of cyclic system Cyclo propane Cyclo Butane Website for CSIR-UGC-NET/JRF, GATE, IIT-JAM, B.Sc. & M.Sc. notes

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Cyclo pentone Cyclo hexane iii) Conformation of cyclohexane derivatvery:iv) Factor affeeting the cyclohexane derivatues:12. Deealins system and its stability:13. Perhydro phenanthrenes and its stability:14. Conformation of perbydroanthracenes: Specific rotation and

15. General Description of Stereoselectivity

Enantiomeric erces

Stereospecipicity Regioseleitivity Chemo selectivity 16. Questions for practice 17. NET / JRF preleions year Questions. 18. GATE Preleious year Questions. Stereochemistry Stereo  Spatial arrangement / 3 D arrangement of atoms or group. It involves the study of relative 3D arrangement of atoms or go. CH 3

CH3

C C2 H5

HO

OH

C

H

C2 H5

H

. 3 d Arrengment / Spatialarrergrrent

2 D arcengmen

ISOMERISM  In Which Different having the same molecule formula ISOMERS

Structural /Constitutional Isomers Diff erent sequ. ence of Bonding of their atoms

Ste reoisomers But redatiue arrengrrent of atoms will be diff ernt .

. Ex

CH3

CH3

C

C

H OH

CH2CH3

H OH s + ( ) ( ) 2 Butanol

CH3 CH2 - (R) ( ) 2 Butano

Types of Constitutional isomers

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i) Chain isomerism ii) Position isomerism iii) Metamerism iv) Tautomerism v) Valenee isomerism vi) Functional group isomeridm Stereoisomers

Conformational Isomer or

Configurational Isomers

Rotomers Enantiomers Enantiomers

Diastereomers

Diastereomers

 Conformational Isomers. Different shapes of molecule by rotation around single bond. zz (I)

and (II) are not mirrop image to each other so they are conformational Diastereaisomers. CH3 H

H

CH3

CH3

CH3 (II) - Trans 2 Butene . as Di tereomers

H

H

(I) cis -2- Butene

Configurational CH3

CH3 D

C D

HO

CH2

C

CH3 CH3

CH2

OH

There two are enantiomens. CH3

CH3

CH3 CH2

H

CH3 C

C H

CH3 CH2

OH

CH3 H

CN

R

H

H

. Conf igurational Diastereoisomers

Some terminology  Optical activity

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H CN

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Those compound which rotate the plane polarized light either left Secretion or right section known as optical active compound and this process as optical activity.  Symmetric atoms archival Compound having minimum any one symmetry. Object or molecule which are super imposable on their mirror image. Br

H Cl

H

H σ + nt

H

Cl

Cl H H

H

Cl Atternate axis of Symmetry.

Plane of symmetry

H Br i + nt

cantce of symmetry

No any symmetry + nt in the molecule. CH 3

CN

Cl C C2 H5

R

H

H

c e tr i mm sy A

con

OH

tre COOH

H

*

H

*

OH

COOH

Plane of symmetry OH Assymmetric contre

. Achiral molecule with two asymmetric contre

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Chiral centre Compound, central atom attached with four different groups and no any symmetry + not on atom. H

Chiral centre

OH

Br

C

C

H3 C

CH3

Cl

Chiral centre

OH

H

H

CH3

achiral centre

Stereogenic Centre Stereocentre.  A stereagenic centre is an atoms having groups of such nature that interchanges of any two groups will produs stereo isomers. Ex:CHO H

CHO OH

C

HO

C

CH 2OH

H

CH 2OH

D Glyceraldehyde (R)

. L Glyceraldehyde (S)

A carbon atom that is a steneocenter is also called steneogenic carbon. R and S Designation from three dimensional Drawing R  Rectus = clockwise S  Sinister = Anticlockwise Acc. to cip rule (Cohn ingold Grelog’s rule) 1) Assign the priority of group attached to stereo cent follow the order of degreasing atomic number. 2) Lowest priority substituent must be away from obseruen 3) Rotate eyes in the decreasing order of priority  Clockwise –R  Anticlockwise –S Sequence rule1) Assign the priority of group Acc. to atomic number of atom directly attached to the centre atom. Heauer atoms should be assign the highest priority. I, (1)

Br, (2)

Cl, (3)

F 4 ( )

(2) F

H (4) C

Cl (1)

CH3 3 ( )

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2) If isotopes of an elements are +nt assign the priority according to mass numbers. 1H ( 3)

1

17H

1H

3 1H ( 1)

2

( 2) 35

17H ( 1)

( 3)

( 3) D

T

( 2)

C CH3 ( 1)

H ( 4)

37

3) It atoms are attached to central atom, then go for the near heaceir atom, Br

(1) CH3 CH3

H

OCH

(4)

(2)

C

C

Br

C

CH 3 CH 2 CH

CH3 (3)

Br

(1) HO

NO 2 (2) CH2 CH

I

CH2 (1)

OH (2)

NH 2

(4) H

(2)

C

(3) CH 3

OH CH

CH 2 (1)

CH3

H

4) If atom attached to double or triple bond, they should be considered as duplicates and triplicates. CH3

CH3

CH3

(1)C CH3 (4) C CH2 (3) C (2) H

CH2 CH3

CH3

C

C

H3C

CH3

C

C

CH

C

C CH3

OH

CH2

CH3 C

C

C

C

 Double bonded attached carbon Count will be double carbon. CH3

C

C

H

CH3

C

C

C

C

C

C

 Triple bonded Carbon atom count triple carbon. (3) CH3 (1) C C H C CH3 CH2 (4) H (2)

C

C

C

C

C

C

C

H

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5)

O

O

C

C

C

C (4 )

CH H

O

CH2 HO 3 ( )

C

H

Br CH 3 (1) (4 )

6) Lone pain should be taken as lower priority of subs his (4) (2) N (3) CH3 H (1) CH2 CH3 (R)

7) If lowest priority group present on herizentas position, rotation of substituent will be opposite direction. (2)COOH ( 3) D

H ( 4) OH ( 1)

'S'

In that care fourth clowej priority group +nt on horizontal position, direction of rotation taken opposition. Rotation arice ‘R’ But actual contusion is ‘S’. 8) If open chain and ring having identical atom then prefer gives to ring always. 2

O

(3 )

(4 ) O

(2 )

(1 )

3

'R' lowest Priority on hozizontal positoin So 'R'

O

4

3

1

(4 )

O

O O

2

2

1

'S'

1

3 4

O OH 3

2

1 O

Br

4

Br 'S '

Cl 3

NO 2 'S '

O 2

4

'R '

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In fuced ring system, assign the configuration Acc. To above or below the plane of group. Firstly pertinence the group attael to stereagenic centre then follow as trick. 1

2

3

4

(+) = as it is

Above the plane

(+)

(-)

(+)

(-)

(-) = opposite

Below the plane

(-)

(+)

(-)

(+)

Q

. N

N

NO2 H

Q

Br

NO2

H

H

B

Br

= CA S = CB R

H

. Br

Br B C A

OH O

OH

H

H

O

H

O

CA = R = CB R = CC R

In this case view from the cavity, so carbons towards the observer and endo bond away from the obscure. O

(1)

( 2)

H ( 2)

C

CH3 CH3 ( 2)

H3C

OH (1)

H ( 4)

C

H CH2OH ( 3)

C ( 1)

C ( 3) ( 4)

( S)

H3C ( 3)

H3C

CH3

( 4)

C ( 3)

C ( 1) ( 2)

( 5)

C O

( 3) NH2OC

H

( S)

C ( 3) O

HS

( 7)

C

NHR O

CH3

CH3 4 C ( )

N

H

C

(6) CH3

CHO (4) COOH ( 2) COOR ( 1) ( S)

CH2 CH3 ( 3)

C NR2 ( 2) ( S) H ( 4)

HO ( 1) (4) CH2

OH

H

CH2

CH2

C ( 2)

N ( S)

CH3

O ( 8) H

( R)

( R)

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O

CH3

(10)

H

CH3 NH2

I II H (R) Is , II R

(11) Me

(R) H

(12)

H

(13)

H

I II (R)

Cl

8

H

(16)

6

1 2

4

Br

H

H

HO

II

II

III

III

Cl H Is , II S III R

(17)

H

IR, IIS

OH

Br

3

5

7

II I

IS, II S

(15) H

H

H

H , IIS IS ] [

Cl

(14)

I II

H

H

Me

COOH

HO

HOOC

(18)

IR, IIR, IIIS

H3C

HO

OH

OH

CH 3

H

H

'R' 'S'

(17)

H

COOH

HO

H 3C

H

Me

HOOC

OH

HO

OH

H

H 'S'

(19) H 3C

CH3

'R'

CH3

(20)

H 3C

I

I II

II CH3 H3C OH IS, IIS

2 CH3

H 3C

OH

IR, IIR

H 3C H 3C

H 3C CH3

H 4

3

O

O

CH3

1 H

H

H 3C

CH3

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(22)

CH3

HO

CH3

(23)

H

HO

HO CH3

H3C

Isomenthol

CH3

H3 C

Neomenthol , , (1S RS 5S)

CH3

Neoiso menshol , , (1R 2R 5R)

(24) CH3

CH3 H H

HO HO

OH

H CH3

H3 C

CH3

H3 C

Menther

I R, 2S, 5R

CH3

(25)

I

I

H

H

III

II

Br

H

III

II

H Cl O 2N IR, IIR , III R

H

NO2

Cl IS, IIS, IIIS

(26)

(27) NH3

NH3

Br

Cl

CH3

H

H

Br

Cl

H

H

Cl Cl CR'

C S'

(28)

Br

(29)

Br Br H

IR, IIR

H

HO H

OH IS, IIS

(30)

IS, IIS

H

H

OH

IR, IIR

H

H O

H

OH

Br

H H

H

O

H IR, IIS

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H 3C

H

H

O

O

I

(32)

CH 3 CH3 I

II

II

(32) H I

H

H

O

H IS, IIR

O I

II H IS, IIR

H

I II III

I

OH

H

OH

CHO H

OH

HO

OH

H

OH

H

CH2OH

(36)

H

IS, IIS, IIIS

(36)

H

H

H

CHO OH

II

III

OH

OH

IR, IIR, IIIR

H

CH3

H

H

H

IR, IIS

CH3

CH3 H

(35)

H IS, IIR

(33)

H

IR, IIS

(34) H3C

II

H IS, IIS

II H

I

O

II

H IR, IIS

H IS, IIS

H H I

OH

CH2OH - ucec D gl l

HO H HO HO

CHO S R S S

OH OH H H

CH2OH L glucocl

OH

H (4)

H

O OH

(5)

OH

HO (3)

(6) H (2) H

H OH , , IIIS, IV S, V R 1R IIR ) (

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Symmetry with molecular f ormula

No

Yes

Isomers

Homomers

some bonding Coonnectivity No

Yes

Constitutional isomer (Onisometric)

Stereoisomers object and mirror image No

Yes

Diastereomers (anicometric) Energy barrier

Enantiomers (Isometric) Energy barrier High

Conf ormational Enantiomers

Conf igurational Enantiomers

low

High

low

Conf igurational Diasteceomers

Conf ormational Diastereomer

Enantiomers  Enantiomers are structures that are Non – sperimposable. But they are mirror image to each other. Br

Br Cl

Cl

F

F

* The physical and chemical Properties of enantiomers are . identical

I (B)

I A ( )

* A pair Enontiomers are mirror image f orm of some compound and have opposite absolute Steceochemistry.

 These structure (A) and (B) mirror image to each other but they are Non sperimposable to each other. So they are enantiomers. mirror HO

Et

CN

CN

Me

Me

OH

me = CH 3 Et = CH2 CH3

Et

Enantiomers. mirror

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H

C

O

C

OH

O

CH2OH

H

CH 2OH

D Glycoraldehyde

L Glyceraldehyde

O

C

HO

C

H

H

C

OH

OH

HO

C

H

OH