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1 Types of Organic Compounds organic compounds.Vast majority of over 20 million known compounds are based on C: organic compounds. Generally contain C.

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Presentation on theme: "1 Types of Organic Compounds organic compounds.Vast majority of over 20 million known compounds are based on C: organic compounds. Generally contain C."— Presentation transcript:

1 1 Types of Organic Compounds organic compounds.Vast majority of over 20 million known compounds are based on C: organic compounds. Generally contain C and H + other elements

2 2 Isomerism Isomers have identical composition but different structuresIsomers have identical composition but different structures Two forms of isomerismTwo forms of isomerism –Constitutional (or structural) –Stereoisomerism ConstitutionalConstitutional –Same empirical formula but different atom- to-atom connections StereoisomerismStereoisomerism –Same atom-to-atom connections but different arrangement in space.

3 22.3 Isomers > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Look below at the structures of butane and 2- methylpropane. Constitutional Isomers Butane2-methylpropane

4 22.3 Isomers > 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Even though both compounds have the formula C 4 H 10, their boiling points and other properties differ. structuresBecause their structures are different, they are different substances. different structuresisomers have the same molecular formula but different molecular structures. Constitutional Isomers

5 22.3 Isomers > 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Butane and 2-methylpropane represent a category of isomers called constitutional isomers, or structural isomers. Constitutional isomers are compounds that have the same molecular formula but the atoms are joined together differently. Constitutional Isomers

6 22.3 Isomers > 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Constitutional isomers differ in physical properties such as boiling point and melting point. They also have different chemical reactivities. In general, the more highly branched the hydrocarbon structure is, the lower the boiling point of the isomer will be compared with less branched isomers. Constitutional Isomers

7 22.3 Isomers > 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Butane2-methylpropane Which of these molecules will have a lower boiling point and why? 2-methylpropane will have a lower boiling point because it has a more highly branched structure.

8 8 Structural Isomers

9 9 Hydrocarbons & Structural Isomerism C 5 H 12 has 3 structural isomers. Isomers of C 5 H 12 ? Note names of isomers

10 22.3 Isomers > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Stereoisomers What are two types of stereoisomers? Stereoisomers

11 22.3 Isomers > 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Because molecules are three- dimensional structures, molecules with the same molecular formula and with atoms joined in exactly the same order may still be isomers. Stereoisomers are molecules in which the atoms are joined in the same order but the positions of the atoms in space are different. Stereoisomers

12 22.3 Isomers > 12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Two arrangements are possible for the methyl groups and hydrogen atoms with respect to the rigid double bond in 2-butene. Stereoisomers Cis configurationTrans configuration Two types of stereoisomers are cis-trans isomers and enantiomers.

13 22.3 Isomers > 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Cis-trans isomers, also known as geometric isomers, have atoms joined in the same order but the spatial orientation of the groups differs. The most common example of cis-trans isomerism occurs in molecules with double bonds. Stereoisomers Cis-Trans Isomers

14 22.3 Isomers > 14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. In the cis configuration, similar groups are on the same side of the double bond. Stereoisomers Cis-Trans Isomers Cis configuration

15 22.3 Isomers > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. But, when similar groups extend from opposite sides of the double bond, the isomer is in the trans configuration. Stereoisomers Trans configuration

16 22.3 Isomers > 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Cis-trans isomers have different physical and chemical properties. You should be able to identify cis-trans isomers of alkenes when each carbon of the double bond has one substituent and one hydrogen. Stereoisomers Cis-Trans Isomers

17 17 Optical isomers are molecules with non-superimposable mirror images.Optical isomers are molecules with non-superimposable mirror images. Such molecules are called CHIRALSuch molecules are called CHIRAL Pairs of chiral molecules are enantiomers.Pairs of chiral molecules are enantiomers. Chiral molecules in solution can rotate the plane of plane polarized light.Chiral molecules in solution can rotate the plane of plane polarized light. Stereoisomers: Optical

18 18 Chiral Compounds and Polarized Light

19 22.3 Isomers > 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A carbon with four different atoms or groups attached is an asymmetric carbon. In the compound shown here, H, F, Cl, and Br atoms are attached to a single carbon atom, so the carbon is an asymmetric carbon. Stereoisomers Enantiomers CHFClBr

20 22.3 Isomers > 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Stereoisomers Enantiomers The relationship between the two molecules is similar to the relationship between right and left hands. Sometimes the terms right-handed and left- handed are used to describe compounds with an asymmetric carbon.

21 22.3 Isomers > 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. By contrast, a pair of hands is distinguishable even though the hands have identical parts. When you try to stack your hands on top of one another, the thumb of one hand lines up with the little finger of the other hand. No matter how you turn your hands, you can’t get them to look exactly alike. Stereoisomers Enantiomers

22 22.3 Isomers > 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Pairs of molecules that are mirror images and not superimposable are called enantiomers, or optical isomers. These molecules are examples of enantiomers. Stereoisomers Enantiomers

23 23 Stereoisomers Isomers Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid

24 24 Stereoisomers Isomers Lactic acid isomers are non-super- imposable

25 25 Chirality: Handedness in Nature These molecules are non-superimposable mirror images.

26 26 Chirality: Handedness in Nature These amino acids are non- superimposable mirror images.

27 27 Stereoisomers in Nature Right- and left- handed seashells The DNA here is right-handed

28 22.3 Isomers > 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Unlike other isomers, enantiomers have identical physical properties such as boiling points and densities. Enantiomers do, however, behave differently when they interact with other molecules that have asymmetric carbons. Many molecules in your body have asymmetric carbons, so each enantiomer can have a different effect on the body. Stereoisomers Enantiomers

29 22.3 Isomers > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 22.4 Identifying Asymmetric Carbon Atoms Which compound has an asymmetric carbon? a. b.

30 22.3 Isomers > 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 22.4 Analyze Identify the relevant concepts. An asymmetric carbon has four different substituents attached. 1

31 22.3 Isomers > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 22.4 Solve Apply the concepts to this problem. Draw the structure in a way that makes it easier to compare the four different groups attached to the central carbon. a.b. 2

32 22.3 Isomers > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solve Apply the concepts to this problem. Compare the groups. If all four groups are unique, the central carbon is asymmetric. If any two are the same, the central carbon is not asymmetric. a.b. Compound (b) is asymmetric. Sample Problem

33 22.3 Isomers > 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Constitutional isomers differ in physical properties such as boiling point and melting point. They also have different chemical reactivities. Two types of stereoisomers are cis-trans isomers and enantiomers. Key Concepts

34 22.3 Isomers > 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. isomers: compounds that have the same molecular formula but different molecular structures constitutional isomers: compounds that have the same molecular formula, but whose atoms are bonded in a different order stereoisomers: molecules that have atoms in the same order, but which differ in the arrangement of the atoms in space cis-trans isomers: compounds that have atoms in the same order, but differ in the orientation of groups around a double bond Glossary Terms

35 22.3 Isomers > 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. cis configuration: the configuration in which substituent groups are on the same side of a double bond trans configuration: the configuration in which substituent groups are on the opposite sides of a double bond asymmetric carbon: a carbon atom that has four different atoms or groups attached enantiomers: molecules that differ from one another in the way that four different groups are arranged around a carbon atom Glossary Terms


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