Principles in STEREOCHEMISTRY

Prof.Dr \ Adel SelemBy: Mahmoud Galal Zidan

Lecture 1

Historical Background• What is the mean of specific optical rotation ?

• it’s the optical rotation for a solution one gram of soln. at concentration = 1 and length of the tube = 1

• Or it’s an optical rotation of substance solution of 1 gram/100ml concentration present in tube has distance 1 cm .

• Discuss the bonding in CH4 ?

• Carbon always Tetravalent except Carbon monoxide ( CO2 is divalent) • Carbon in excited state

مع الكربون يتفاعل به 4عندما الميثان مثل تداخل يعمل هيدروجين H 3ذراتال لكن و الكربون ذرة من أضعف أو أقوي األخرى و متساويين .4متساوين روابط

بين اإللكترونات ليس و المدارات بين تهجين يسمي s & pفيحدث ما هذا وhybridization .

أن متماثلة .s | sp3بما الروابط كل يبقي متماثلين

•Discuss the bonding in NH3 ?

Acidimetric carbon atom which attached with four different function

• 2-butanol

OH

C2H5OH

HH

OHC2H5 C2H5

H OH

C2H5

OH H

• 2 Cl – Butane

• Lactic acid (2-Hydroxypropionic acid )

athematric carbon

Cl

Isomerism 2n where n is the no of athemetric Carbon

O

OHOH

Carbon not athemetric because of C=O

Pair of enantiomers • Are two optically active isomers each one is the mirror image of

the other • They have identical properties • One of them rotate the light to the right an another rotate the

light to the left

Racemic Mixture • When two enantiomers are mixed together a rotation caused

by a molecule of one isomer is exactly canceled by an equal and opposite rotation caused by a molecule of its enantiomer

• Or it’s the mixture of equal amount of optical inactive .

Compound containing one asymmetric carbon atom

• Glyceraldehyde C3H6O3 ( CnH2nOn )

d(-)d(+)

d-glyceraldhyde

CHO

CH2OH

H OH

CHO

CH2OH

OH H

Compound containing two dissimilar asymmetric carbon atom

• aldoTetriose

D(+) L(-) D(-)L(+)

CHO

H OH

CH2OH

H OH

CHO

CH2OH

OH H

OH H

H OH

CHO

CH2OH

OH H

CHO

CH2OH

H

OH H

OH

OH In right DOH In left L

Diastereomers (1,4) . (2,3) one of the is not mirror image to other but they are non super possible – they have different physical properties .• 2,3 dichloropentane

• Amino Acid ( alanine )

CH2CH3

Cl

Cl

H

H

COOH

R

N2H H

Compound containing two similar asymmetric carbon atom

• 2,3 dichloropentane

Me

Me

Me

Me

Cl

Cl

H

H

HCl

Cl H

Me

Me

H

H

Cl

Cl

Me

M

ClH

HCl

• Aldopentose

OH

OH

OH

CH2OH

OH

H

H

H

O H

OH

OH

CH2OH

OH

H

H

H

O H

OH

H

CH2OH

OH

OH

H

H

O H

H

OH

CH2OH

H

H

OH

OH

O H

OH

OH

CH2OH

H

H

H

OH

O H

H

H

CH2OH

OH

OH

OH

H

O H

H

OH

CH2OH

OH

H

OH

H

O H

OH

H

CH2OH

H

OH

H

OH

Lecture 2

Absolute Configuration • Chloro Bromo Iodo Methane

• Mesoform : is the isomers containing plane of symmetry S R

S R

I

Br

H

Cl

I

Cl

H

Br

H

Cl

BrI

H

Cl

Br I

CH2OH

CH2OH

OHH

OHHPlane of symmetry

• Glyceraldehyde

S R S R

R SS R

Me

HOH2COH

HMe

HOH2COH

HMe

HOH2CCHO

OHMe

HOH2CCHO

OH

H

OH

HOH2C CHO

H

OH

CH2OHCHO

CHO

CH2OH

OH

CHO

CH2OH

HOHH

• Aldo Tetrose

• Tartaric acid (2R,3R) (2S,3S) (2R,3S) (2S,3R)

CHO

H OH

CH2OH

H OH

CHO

CH2OH

OH H

OH H

H OH

CHO

CH2OH

OH H

CHO

CH2OH

H

OH H

OH

(2R,3R) (2S,3S) (2R,3S) (2S,3R)

Mesoform

COOH

H OH

COOH

H OH

COOH

COOH

OH H

OH H

H OH

COOH

COOH

OH H

COOH

COOH

H

OH H

OH

• Aldopentose

(2R,3R,4R) (2S,3S,4S) (2R,3S,4R)

(2S,3S,4R) (2R,3R,4S) (2R,3S,4S) (2S,3R,4R)

(2S,3R,4S)

OH

OH

OH

CH2OH

OH

H

H

H

O H

OH

OH

CH2OH

OH

H

H

H

O H

OH

H

CH2OH

OH

OH

H

H

O H

H

OH

CH2OH

H

H

OH

OH

O H

OH

OH

CH2OH

H

H

H

OH

O H

H

H

CH2OH

OH

OH

OH

H

O H

H

OH

CH2OH

OH

H

OH

H

O H

OH

H

CH2OH

H

OH

H

OH

Racemic Mixture • Formation of ( Cyano hydrides )

• Formation of ( α – halo acid )

HCN

50% 50%

H / H2O

50% 50%

any aldhyde gives racemic mixture

O

HMe CN

H

OH

Me CN

H

OH

Me COOH

H

OH

Me COOH

H

OH

Br2/ FeBr3

Cl2/FeCl3

R COOH R COOH

Br

H

R COOH

Br

H

R COOH

Cl

H

R COOH

Cl

H

• Malonic Ester

NaEt/EtOH RX

NaEt/EtOH

RX

H/H2OHeat

-CO2

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

Na R

R1R

COOH

COOH

R1R

H

COOH

R1R

H

COOH

R1R

• Ethyl acetate

RX

H2O , heatLiAlH4/Na

Me COOEt O - Et C2H- COOEt OH Et

Me COOEt MeO

OEtMe

O -

OEt

COOEtMe

OCOOEt

Me

OCOOEt

Na OEt

OH Et Me

OCOOEt

Na

Me

OCOOEt

R

Na OEt

OH Et

Me

O

COOEt

R

R

Me

O

R

R

Me

OH

R

R