Isomerism Molecules with same molecular formula but diff arrangement of atom Two types of Isomerism Positional Chain Isomer Functional Gp Isomer C – C – C – C – OH C 4 H 10 O 1 Structural Isomerism • Same molecular formula • Diff structural formula • Diff arrangement of atom Diff hydrocarbon chain skeleton • Same molecular formula • Same structural formula/ same connectivity • Diff spatial arrangement of atom Stereoisomerism Hydrocarbon Chain Isomer Diff functional gp position Diff functional gp C – C – C – OH ׀CH 3 C – C – C –C ׀OH C – C – C – C ׀OH C – C – C – C ׀OH C – C – C – O – C Optical Isomer Geometric Isomer Click here khan organic videos. Compound Ethane Ethanoic acid Empirical formula CH 3 CH 2 O Molecular formula C 2 H 6 C 2 H 4 O 2 Full SF Condensed SF CH 3 CH 3 CH 3 COOH Stereochemical formula (3D) Isomer Physical property Chemical property Structural isomer - Hydrocarbon chain - Functional gp position - Functional gp Different Different Different Similar Similar Different Geometrical isomer Different Similar Optical isomer Similar Similar H H ׀ ׀H - C – C – H ׀ ׀H H H O ׀‖ H - C - C - OH ׀H Structural formula – arrangement atoms in molecule (2/3D) H H ׀ ׀H - C – C – H ׀ ׀H H CH 3 CH 3 ethane Display full SF Condensed SF Ball/stick model Spacefilling Click here chemical search. same connectivity but diff spatial arrangement
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IB Chemistry on Stereoisomers, E/Z, Cis Trans, Geometric, Optical and Polarimetry
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Isomerism Molecules with same molecular formula but diff arrangement of atom
Two types of Isomerism
Positional Chain Isomer Functional Gp Isomer
C – C – C – C – OH
C4H10O1
Structural Isomerism
• Same molecular formula • Diff structural formula • Diff arrangement of atom
Diff hydrocarbon chain skeleton
• Same molecular formula • Same structural formula/ same connectivity • Diff spatial arrangement of atom
Stereoisomerism
Hydrocarbon Chain Isomer
Diff functional gp position Diff functional gp
C – C – C – OH
׀
CH3
C – C – C –C
׀
OH
C – C – C – C
׀
OH
C – C – C – C
׀
OH
C – C – C – O – C
Optical Isomer Geometric Isomer
Click here khan organic videos.
Compound Ethane Ethanoic acid
Empirical formula CH3 CH2O
Molecular formula C2H6 C2H4O2
Full SF
Condensed SF CH3CH3 CH3COOH
Stereochemical formula
(3D)
Isomer Physical property
Chemical property
Structural isomer - Hydrocarbon chain - Functional gp position - Functional gp
Different Different Different
Similar Similar
Different
Geometrical isomer Different Similar
Optical isomer Similar Similar
H H
׀ ׀
H - C – C – H
׀ ׀
H H
H O
‖ ׀
H - C - C - OH
׀
H
Structural formula – arrangement atoms in molecule (2/3D)
H H
׀ ׀
H - C – C – H
׀ ׀
H H
CH3CH3
ethane
Display full SF Condensed SF Ball/stick model Spacefilling
• Same molecular formula • Diff structural formula • Diff arrangement of atom
• Same molecular formula • Same structural formula/same connectivity
• Diff spatial arrangement of atom
Stereoisomerism
Hydrocarbon Chain Isomer
Optical Isomer Geometric Isomer
Requirement for geometric isomers • Presence of C=C double bond - prevent bond rotation • Presence of ring structure - prevent bond rotation • Carbon atom in double bond bonded to diff atom
Cis Isomers Atom located on same side
Trans Isomers Atom located on diff side
Presence C=C Presence of ring structure
CI CI
׀ ׀
C = C
׀ ׀
H H
Cis 1, 2 dichloroethene
CI H
׀ ׀
C = C
׀ ׀
H CI
Trans 1, 2 dichloroethene
Cis 1, 2 dichlorocyclopropane Trans 1, 2 dichlorocyclopropane
Carbon atom bond to diff atom
double bond
C – C – C – C – OH C – C – C –C
׀
OH
C – C – C – O – C
C – C – C – OH
׀
CH3
CI CI CI
CI
H
H H H
CI CI
H H
H
H
CI
Cis 1, 3 dichlorocyclobutane Trans 1, 3 dichlorocyclobutane
same atom
different atom χ
✓
No geometric isomers
Geometric isomers
same connectivity but diff spatial arrangement
• Same molecular formula • Same structural formula/same connectivity
• Diff spatial arrangement of atom
Stereoisomerism
Geometric Isomer
Requirement for geometric isomers • Presence of C=C double bond - prevent bond rotation • Presence of ring structure - prevent bond rotation • Carbon atom in double bond bond to diff atom
Cis Isomers Atom located on same side
Trans Isomers Atom located on diff side
Presence C=C Presence of ring structure
CI CI
׀ ׀
C = C
׀ ׀
H H
Cis 1, 2 dichloroethene
CI H
׀ ׀
C = C
׀ ׀
H CI
Trans 1, 2 dichloroethene Cis 1, 2 dichlorocyclopropane Trans 1, 2 dichlorocyclopropane
1. Light pass through 1st polariser – plane polarised light produced
2. Sample introduce to tube. Sample is optically active
Rotate plane of polarised light to one direction
3. Turn analyzer either clockwise/anticlock wise to give light of max intensity again
4. If sample rotate light 120 clockwise – Analyzer need to rotate anticlock wise 120
5. If one enantiomer rotate light 120 clockwise
Another enantiomer rotate light anticlock wise 120
How polarimeter detect optical isomer ?
6. Racemic Mix = enantiomers in equal amt (equimolar) , cancel each other rotation
1st polarizer
1st polarizer
sample optically active
sample optically inactive = Optical activity ability- to rotate plane of polarised light Optically active isomers – presence of asymmetrical/chiral centre - carbon bond to 4 diff gp
Product from natural sources/catalysed by enzyme • give 1 pure optically active enantiomer • chiral and found in single enantiomer – optically active
Products synthesised chemically • give 2 enantiomer in equal amt /racemic mix • optically inactive rotation cancel out each other
Light source
1st polarizer
Tube containing sample which able to rotate polarized light
Product from natural source/catalysed by enzyme • give 1 pure optically active enantiomer • chiral and found in single enantiomer – optically active
Product synthesised chemically • give 2 enantiomer in equal amt /racemic mix • optically inactive rotation cancel out each other
R – inactive Racemate mix ibuprofen
S – active Racemate mix ibuprofen
Ibuprofen (painkiller) R limonene S limonene
CH3
CH3
CH3
Stereoisomerism
Mirror image / enantiomers Same chemical/physical property except rotation of polarized light
Source/smell orange
Source/smell lemon
Mirror image / enantiomers Same chemical/physical property except rotation of polarized light
R carvone S carvone
Mirror image / enantiomers Same chemical/physical property except rotation of polarized light
Source/smell spearmint
Source/smell caraway seed
R Thalidomide (sedative) S Thalidomide (teratogenic)
• Drug company make drug with R and S (racemic mix) • Thalidomide exist as optical isomers • Enantiomers (R) and (S) • (R) effective against morning sickness • S teratogenic, birth and limb defect
Our body synthesise enzyme which have active site for only one enantiomer
Mirror image / enantiomers
Thalidomide (pregnancy)
• (S) cause limb defect / shortening of arm /leg • (R) is effective drug • Body convert (R) to (S) by racemisation process, produce racemic mix (R)/(S)
• Most drug in racemic mix equal (R) and (S)
• Cheaper to synthesise racemic mix than pure enantiomer
• Single enantiomer appear to be more effective than racemic mix
• Clinical trial is essential to ensure no harmful side effect
(S), effective as pain relief (R) has no side effect!
March 2010 - Published in Science by Takumi Ito. Click HERE for info
Defect Limb due to Thalidomide • (S) bind /inactivate protein cereblon, which involve in limb formation. • Inactivation, lead to a teratogenic effect on LIMB DEFORMITIES
Published in Science ..... • Hiroshi Handa /Takumi Ito - Developed tiny beads with Thalidomide attach. • Thalidomide beads mix with cells extract • Protein Cereblon was bounded on beads • Lack Protein Cereblon during embryo development, cause limb deformities
Scientist discovered how Thalidomide caused Malformed Limb
History of Thalidomide 1954 - Thalidomide for morning sickness. 1961 - Withdrawn, teratogenicity, birth defects result .
1990 - FDA approved for leprosy (skin disease) 1998 - FDA approved for multiple myeloma, (cancer of plasma cells in blood)
2004 - Lenalidomide derived from Thalido able to strengthen immune cells and effective against blood cancers 2011 - Thalidomide + Lenalidomide inhibit formation of new blood vessels ( anti-angiogenic) of tumor cells, Tumors unable to grow due to lack of nutrition. Researchers testing thalidomide in trials for other HIV and Crohn’s disease.