1. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Sections 25.1-25.3 Organic Chemistry Chemistry, The Central Science, 11th edition Brown & LeMay

2. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Chemistry Organic chemistry is the chemistry of carbon compounds. Carbon has the ability to form long chains. Without this property, large biomolecules such as proteins, lipids, carbohydrates, and nucleic acids could not form.

3. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Carbon Compounds There are three hybridization states and geometries found in organic compounds: –sp 3 Tetrahedral –sp 2 Trigonal planar –sp Linear

4. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Hydrocarbons There are four basic types of hydrocarbons: –Alkanes –Alkenes –Alkynes –Aromatic hydrocarbons

5. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkanes Alkanes contain only single bonds. They are also known as saturated hydrocarbons. –They are “saturated” with hydrogens.

6. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Formulas Lewis structures of alkanes look like this. They are also called structural formulas. They are often not convenient, though…

7. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Formulas …so more often condensed formulas are used.

8. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Properties of Alkanes The only van der Waals force is the London dispersion force. The boiling point increases with the length of the chain.

9. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkanes Carbons in alkanes are sp 3 hybrids. They have a tetrahedral geometry and 109.5° bond angles.

10. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkanes There are only  - bonds in alkanes. There is free rotation about the C—C bonds.

11. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Isomers Isomers have the same molecular formulas, but the atoms are bonded in a different order.

12. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature There are three parts to a compound name: –Base: This tells how many carbons are in the longest continuous chain.

13. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature There are three parts to a compound name: –Base: This tells how many carbons are in the longest continuous chain. –Suffix: This tells what type of compound it is.

14. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature There are three parts to a compound name: –Base: This tells how many carbons are in the longest continuous chain. –Suffix: This tells what type of compound it is. –Prefix: This tells what groups are attached to the chain.

15. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. How to Name a Compound 1.Find the longest chain in the molecule. 2.Number the chain from the end nearest the first substituent encountered. 3.List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached.

16. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. How to Name a Compound If there is more than one type of substituent in the molecule, list them alphabetically.

17. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Cycloalkanes Carbon can also form ringed structures. Five- and six-membered rings are most stable. –They can take on conformations in which their bond angles are very close to the tetrahedral angle. –Smaller rings are quite strained.

18. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkanes Alkanes are rather unreactive due to the presence of only C—C and C—H  -bonds. Therefore, they make great nonpolar solvents.

19. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkenes Alkenes contain at least one carbon–carbon double bond. They are unsaturated. –That is, they have fewer than the maximum number of hydrogens.

20. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkenes Unlike alkanes, alkenes cannot rotate freely about the double bond. –The side-to-side overlap in the  -bond makes this impossible without breaking the  -bond.

21. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkenes This creates geometric isomers, which differ from each other in the spatial arrangement of groups about the double bond.

22. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Properties of Alkenes Structure also affects the physical properties of alkenes.

23. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Nomenclature of Alkenes The chain is numbered so the double bond gets the smallest possible number. cis-Alkenes have the carbons in the chain on the same side of the molecule. trans-Alkenes have the carbons in the chain on opposite sides of the molecule.

24. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkenes One reaction of alkenes is the addition reaction. –In it, two atoms (e.g., bromine) add across the double bond. –One  -bond and one  -bond are replaced by two  -bonds; therefore,  H is negative.

25. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions It is a two-step mechanism: –The first step is the slow, rate-determining step. –The second step is fast.

26. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions In the first step, the  -bond breaks and the new C—H bond and a cation form.

27. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions In the second step, a new bond forms between the negative bromide ion and the positive carbon.

28. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkynes Alkynes contain at least one carbon–carbon triple bond. The carbons in the triple bond are sp-hybridized and have a linear geometry. They are also unsaturated.

29. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Nomenclature of Alkynes The method for naming alkynes is analogous to the naming of alkenes. However, the suffix is -yne rather than -ene. 4-methyl-2-pentyne

30. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkynes Alkynes undergo many of the same reactions alkenes do. As with alkenes, the impetus for reaction is the replacement of  -bonds with  -bonds.

31. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Aromatic Hydrocarbons Aromatic hydrocarbons are cyclic hydrocarbons that have some particular features. There is a p-orbital on each atom. –The molecule is planar. There is an odd number of electron pairs in the  - system.

32. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Aromatic Nomenclature Many aromatic hydrocarbons are known by their common names.

33. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds In aromatic compounds, unlike in alkenes and alkynes, each pair of  -electrons does not sit between two atoms. Rather, the electrons are delocalized; this stabilizes aromatic compounds.

34. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds Due to this stabilization, aromatic compounds do not undergo addition reactions; they undergo substitution. In substitution reactions, hydrogen is replaced by a substituent.

35. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Aromatic Compounds Two substituents on a benzene ring could have three possible relationships: –ortho-: On adjacent carbons. –meta-: With one carbon between them. –para-: On opposite sides of ring.

36. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds Reactions of aromatic compounds often require a catalyst. Halogenation Friedel-Crafts Reaction