Prepared byLawrence Kokhttp://lawrencekok.blogspot.com

Stereoisomerism, Geometrical, Cis Trans and Optical Isomerism 

Stereoisomerism are isomer with same Molecular Formula + Structural Formula but different in spatial arrangement ( different 3 Dimensional shapes )

2 types of Stereoisomers for ORGANIC compounds• geometrical• optical 

• Chiral carbon • 4 different gps attached to carbon central• Non superimposable• Mirror image ( right, left handed )• Asymmetrical carbon • Enantiomers• Identical chemical/physical properties • 2 enantiomers rotate plane of polarised light to diff directions

Optical Isomers (Organic)

Geometrical Isomers (Organic)

• Cis, gps on adjacent sides• Trans, gps on opposite sides• Restricted movement• Double bond• Ring structured

• Non superimposable• Mirror image, Enantiomers• Identical chemical/physical properties • 2 enantiomers rotate plane of polarised light to diff directions

Optical Isomers (Inorganic)

• Coordination compounds with ligands attach• Central atom is Transition metal• Ligands are electrons donors• Cis / trans 

Geometrical Isomers (Inorganic)

picture taken fromhttp://www.chemguide.co.uk/inorganic/complexions/shapes.html

• Pi bonds to prevent free rotation• Different gps attached to carbon 

• Ring formation, restricted rotation ( CI are located on top and cannot be rotated to bottom)

3 Criteria for Geometrical isomerism

picture taken fromhttp://www.freewebs.com/hydrocarbons_chemistry/cyclichydrocarbons.htmhttp://www.chemguide.co.uk/basicorg/isomerism/geometric.html

IB examples on Geometrical Isomerism1st Cis Butenedioic /maleic acid

• Low m/p, soluble• Strong intramolecular H2 bonding• Weak intermolecular H2 bonding• Anhydride formation(heated)

• High m/p, insoluble• Weak intramolecular H2 bond• Strong intermolecular H2 bond• No anhydride formation

Click HERE for Synthesis and Answers for m/p and b/ppicture fromhttp://courses.chem.indiana.edu/c122/documents/Experiment2.pdf

Trans Butenedioic/fumaric acid

2nd Cis/Trans (1,2 dichloroethene)

 m/p                    b/p

Trans         -50 (higher)       48 (lower)Cis             -80 (lower)         60 (higher)

3rd Cis/Trans (but 2ene)

  m/p                     b/pTrans         -106 (higher)       1 (lower)      Cis             -139 (lower)         4 (higher)

Why Cis/Trans have diff b/p and b/p?

Differences in m/p and b/p Cis/Trans (1,2 dichloroethene)

Cis b/p high - polar (net dipole moment )Cis m/p low - unable to pack (bend/kink)

Trans b/p low - non polar (bond polarity cancel)Trans m/p high - pack together ( linear )

Packing causes molecules to align/pack closer together, greater surface area, stronger VDF, higher m/p

Cis m/p low - no packing ( bend/kink)Cis b/p high - polar ( net dipole moment)

Trans m/p high - packing ( linear )Trans b/p low - non polar (bond polarity cancel)

Packing cause molecules to align closer together, greater surface area, stronger VDF, higher m/p

Cis/Trans (but 2ene)

Medical Uses Cis/Trans (Geometric Isomer) in Cancer Treatment.

Cisplatin, chemotherapy drug for cancers of testicular, ovarian, stomach and prostate cancers.(killing tumor cells that are rapidly dividing. Platinum complexes works as an alkylating agents binding to DNA, prevent DNA replication and triggers apoptosis( cell death)  

picture fromhttp://withfriendship.com/user/vinus/cisplatin.php

How Cisplatin works

• Cisplatin, (Pt2+ with 2Cl−) neutral molecule enters the cell• Cl− dissociate, replaced by water ( ligand displacement, aquation rxn )• Cisplatin becomes positively charged Pt2+ (loss of Cl− ligand)• Attracted to DNA (negatively charged)• Water ligand form H2 bond with G base of DNA• Chelate / alkylate the DNA, prevent DNA replication

• Cisplatin , neutral and square planar, penetrate cell membrane easily• In the cell, CI ligand will be replaced by H2O ( ligand substitution )• H2O will hydrogen bond ( intramolecular H bond) with guanine (G)• DNA unable to replicate properly• Attack normal cells, rapid multiplying cell like bone marrow cells ( side effect)

Keywords for IB HL

New version now includes Carboplatin and OxaliplatinHow new version platinum anticancer works

• Ligands COOH group is used• Water replaces COOH group• H2 bonding with DNA• Mechanism very similar with Cisplatin

Mechanism for Carboplatin

• Binds to tumor replicating DNA• H2 bond with Guanine base (G)• DNA replication stops

Source:https://www.llnl.gov/str/March07/Felton.html

Advantages of Carboplatin over Cisplatin

Lower reactivity, Less toxic, Longer half life, Less side effect, Less kidney damaged

Disadvantages of Chemotherapy DrugsDestroy rapid multiplying cell of mouth, stomach, bowel, hair follicles and bone marrow cells - resulting in low blood counts.

• Side effect is hair loss due to destruction of rapid dividing hair cells• Cisplatin and chemotherapy drug, unable to differentiate tumor cells from normal dividing cells.

Picture taken fromhttp://science.kukuchew.com/2008/10/06/chemotherapys-side-effect-hair-loss/

Video on the mechanism of Cisplatin (Chemotherapy Drug)

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com