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CONSTITUTIONAL ISOMERS Isomers with a different order of attachment of the atoms in their molecules STEREOISOMERS Isomers with the same order of attachment,

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Presentation on theme: "CONSTITUTIONAL ISOMERS Isomers with a different order of attachment of the atoms in their molecules STEREOISOMERS Isomers with the same order of attachment,"— Presentation transcript:

1 CONSTITUTIONAL ISOMERS Isomers with a different order of attachment of the atoms in their molecules STEREOISOMERS Isomers with the same order of attachment, but a different configuration (3D arrangement) of groups on one or more of the atoms ISOMERS Different compounds with the same molecular formula cis/trans ISOMERS ENANTIOMERS Stereoisomers whose molecules are non- superimposible mirror images of each other DIASTEREOMERS Stereoisomers whose molecules are not mirror images of each other Each isomer could have stereoisomers double bond or ring both can apply with a ring TYPES OF ISOMERISM (geometric)

2 Relationship of Constitutional and Stereoisomers

3 Relationships of Stereoisomers

4 FISCHER PROJECTIONS

5 في الكيمياء ( وخاصة الكيمياء العضوية والحيوية), يعنى مسقط فيشر تمثيل ثنائي الأبعاد للجزيء العضوي ثلاثي الأبعاد كمسقط. يتم رسم جميع الروابط كخطوط أفقية أو عمودية.الكيمياء العضويةوالحيويةللجزيء العضوي ويتم تمثيل سلسلة الكربون رأسيا, وتمثيل ذرات الكربون بمركز الخطوط المتقاطعة. كما يتم تمثيل ذرة الكربون الأولى C1 في الأعلى. وقد تم تقديم مسقط فيشر بواسطة إيميل فيشر.الكربونإيميل فيشر

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7 فى مسقط فيشر, كل الروابط الأفقية يتم إسقاطها للأمام (كما لو كانت خارجة من الصفحة أو الشاشة). وعلى ذلك, لا يمكن تدوير مسقط فيشر (2n+1) × 90° في مستوى الصفحة أو الشاشة, حيث أن إتجاه الروابط متناسب لبعضه البعض ولذلك يتغير, محور الجزيء إلى مقابله الضوئي.مقابله الضوئي

8 CHO HOCH 2 H OH OHH CHO CH 2 OH H CH 2 OH CHO OH EVOLUTION OF THE FISCHER PROJECTION Substituents will stick out toward you like prongs Fischer Projection Main chain bends away from you Sawhorse Projection Orient the main chain vertically with the most oxidized group at the top.

9 ORIENTATION OF THE MAIN CHAIN AND THE SUBSTITUENTS IN A FISCHER PROJECTION continuation of the main chain OH H H H

10 HH CH 3 CH 3 ClBr CH 3 H H Cl Br main chain in red orient main chain vertically convert to Fischer Projection rotate 90 o Br Cl CH 3 H H

11 DETERMINATION OF DETERMINATION OF R / S CONFIGURATION R / S CONFIGURATION IN FISCHER PROJECTIONS تحديد الهيئة الفراغية المطلقة ( R و S ) من خلال مسقط فيشر

12 H CH 2 OH CHO OH PLACE THE PRIORITY=4 GROUP IN ONE OF THE VERTICAL POSITIONS, THEN LOOK AT THE OTHER THREE H OH OHC CH 2 OH R alternatively: H CH 2 OH CHO OH HOCH 2 CHO OH H R #4 at top position#4 at bottom position BOTH IN BACK SAME RESULT

13 H CH 2 OH CHO OH FOR THE MENTALLY AGILE WHY BOTHER INTERCHANGING? JUST REVERSE YOUR RESULT! H coming toward you Same molecule as on previous slide. S reverse R Same result as before.

14 * * 2 2 = 4 stereoisomers R R S S R S * * * 2 3 = 8 stereoisomers R R R R R S R S R S R R R S S S R S S S R S S S

15 Link to: Drawing Enantiomers and Diastereomers Tutorial and Exercises Tutorials Topic List Stereochemistry Practice Problems

16 Stereospecificity Stereospecificity and stereoselectivity

17 stereospecificity is the property of a chemical reaction that yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditionschemical reactionstereoisomeric reactants

18 stereoselectivity is the property of a chemical reaction that yields an unequal mixture of stereoisomers from a single reactantchemical reactionstereoisomersreactant

19 مقارنــة بـين stereoselectivity describes a reaction where the mechanism allows for the formation of both products, but the formation of one of the products is favored Stereospecificity describes a reaction that necessarily yields a given stereoisomer because of the mechanism of the reaction

20 مقارنة بين stereoselectivity yields an unequal mixture of stereoisomers from a single reactant. stereoisomersreactant Stereospecificity yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditions stereoisomeric reactants

21 مقارنة بين stereoselectivity may be partial, where the formation of one stereoisomer is favoured over the other, or it may be total where only one stereoisomer is formed Stereospecificity always yields 100% of a particular stereoisomer

22 مقارنة بين stereoselectivity An example of partial stereoselectivity is dehydrohalogenation of 2-iodo-butane which yields 80% trans-2-butene and 20% cis-2-butene dehydrohalogenation Stereospecificity For example, the addition of dibromocarbene to cis and trans-2-butene

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25 CONFIGURATION ABSOLUTE CONFIGURATION ( R / S )

26 CONFIGURATION The three dimensional arrangement of the groups attached to an atom Stereoisomers differ in the configuration at one or more of their atoms.

27 2 CONFIGURATION CONFIGURATION - relates to the three dimensional sense of attachment for groups attached to a chiral atom or group of atoms (i.e., attached to a stereocenter). clockwise counter clockwise (rectus)(sinister) view with substituent of lowest priority in back C C RS

28 CONFIGURATION Enantiomers are assigned a CONFIGURATION using the same priority rules we developed for E/Z stereoisomers. 1. Higher atomic number has higher priority. 2. If priority cannot be decided based on the first atom attached move to the next atom, following the path having the highest prioity atom. 3. Expand multiple bonds by replicating the atoms attached to each end of the bond. SPECIFICATION OF CONFIGURATION SEQUENCE RULE CAHN-INGOLD-PRELOG

29 RS Bromochlorofluoroiodomethane Enantiomers

30 How Many Stereoisomers Are Possible? maximum number of stereoisomers = 2 n, where n = number of stereocenters (sterogenic carbons) sometimes fewer than this number will exist

31 IMPORTANCE OF STEREOCHEMISTRY # AN ACHIRAL REAGENT REACTS IDENTICALLY WITH BOTH ENANTIOMERS. # AN ACHIRAL SOCK FITS ON EITHER FOOT # A CHIRAL REAGENT REACTS DIFFERENTLY WITH EACH ENANTIOMERS. # A CHIRAL SHOE FITS ON ONLY ONE FOOT.

32 RECEPTORS ARE PROTEINS THAT BIND PARTICULAR MOLECULES. BECAUSE A RECEPTOR WILL RECOGNISE ONLY ONE OF A PAIR OF ENANTIOMERS, ENANTIOMERS CAN HAVE DIFFERENT PHYSIOLOGICAL PROPERTIES.

33 RECEPTORS LOCATED ON THE EXTERIOR OF NERVE CELLS IN THE NOSE ARE ABLE TO PERCIEVE AND DIFFERENTIATE THE ESTIMATED SMELLS TO WHICH THEY ARE EXPOSED.

34 (R)-(-)-CARVONE IS FOUND IN SPEARMINT OIL AND (S)-(+)- CARVONE IS FOUND IN CARAWAY SEED OIL. EACH HAS A DIFFERENT SMELL AS IT FITS INTO DIFFERENT RECEPTORS.

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36 (S)-(-)-KETAMINE IS FOUR TIMES MORE POTENT THAN (R)-(-)-KETAMINE AND HAS LESS SIDE EFFECTS. THE ACTIVE INGREDIENT OF IBUPROFEN IS THE (S)-(+)-ISOMER.

37 THE STEREOCHEMISTRY OF REACTIONS ARE VERY IMPORTANT. A REGIOSELECTIVE REACTION FORMS MORE OF ONE CONSTITUTIONAL ISOMER THAN THE OTHER. A B + C MORE B IS FORMED THAN C, WHERE B AND C ARE CONSTITUTIONAL ISOMERS.

38 A STEREOSELECTIVE REACTION FORMS MORE OF ONE STEREOISOMER THAN THE OTHER. A B + C MORE B IS FORMED THAN C, WHERE B AND C ARE STEREOISOMERS.

39 IN A STEREOSPECIFIC REACTION, EACH STEREOISOMERIC REACTANT FORMS A DIFFERENT STEREOISOMERIC PRODUCT OR A DIFFERENT SET OF STEREOISOMERIC PRODUCTS. A B C D A AND C ARE STEREOISOMERS B AND D ARE STEREOISOMERS A STEREOSPECIFIC REACTION IS ALSO STEREOSELECTIVE. A STEREOSELECTIVE REACTION IS NOT NECESSARILY STEREOSPECIFIC

40 ALL THE REACTIONS THAT OCCUR IN BIOLOGICAL SYSTEMS ARE CATALYSED BY ENZYMES. AN ENZYME CATALYSED REACTION FORMS ONLY ONE STEREOISOMER BECAUSE AN ENZYME POSSESSES A CHIRAL BINDING SITE. THEY ARE COMPLETELY STEREOSELECTIVE. THE ENZYME FUMARASE, WHICH CATALYSES THE ADDITION OF WATER TO FUMARATE, FORMS ONLY (S)- MALATE.

41 ENZYME CATALYSIS IS STEREOSPECIFIC. AN ENZYME CATALYSES THE REACTION OF ONLY ONE STEREOISOMER. FUMARASE CATALYSE THE ADDITION OF WATER TO FUMARATE BUT NOT TO MALEATE AN ENZYME CAN DIFFERENTIATE STEREOISOMERS BECAUSE OF THE CHIRAL BINDING SITE

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