Chem 150 Unit 2 - Hydrocarbons & Functional Groups

1. Chem 150Unit 2 - Hydrocarbons & Functional Groups • Organic chemistry is the chemistry of carbon. The name “organic” reflect the fact that organic molecules are derived from living organisms. In this unit will start by looking at four families of organic molecules that are grouped together as the hydrocarbons. We will also look at some functional groups that define some of the other families of organic molecules.

2. Organic Chemistry • Organic chemistry is the chemistry of carbon. • There are three forms of pure carbon • Diamond • Graphite

3. Organic Chemistry • Organic chemistry is the chemistry of carbon. • There are three forms of pure carbon • Buckminsterfullerene“Bucky Balls”

4. Hydrocarbons • Organic molecules contain carbon combined with other elements. • Organic molecules are grouped into families • Members of a family share common structural, physical, and chemical characteristics. • There are four families that contain molecules made of only carbon and hydrogen. • Hydrocarbons • Alkanes • Alkenes • Alkynes • Aromatics

5. Hydrocarbons

6. Alkanes • Alkanes are hydrocarbons that contain only carbon-carbon single bonds. • Every carbon atom participates in 4 single bonds, either to another carbon or to a hydrogen. • Every hydrogen atom is bonded to a carbon by a single bond.

7. Alkanes • Alkanes are hydrocarbons that contain only carbon-carbon single bonds.

8. Alkanes • Alkanes in which the carbons are connected in a straight chain are called normal alkanes. • Alkanes that are branched are called branched chain alkanes. n-hexane 2-methyl-pentane

9. Alkanes • For a discusion on the structure of alkanes,see the Unit 2Elaboration - Alkane Structure

10. Alkanes • Alkanes, along with the other hydrocarbons, are non-polar. • They interact with each other only through London dispersion forces. • This is why they have relatively low boiling and melting points.

11. Alkanes • They interact with each other only through London dispersion forces. • Note how the boiling points increase with molecular weight.

12. Molecule in the News

13. Molecule in the News:Melamine

14. Organic Molecules in the News!! • http://www.cbc.ca/health/story/2007/09/06/additives-lancet.html?ref=rss • http://www.medpagetoday.com/Psychiatry/ADHD-ADD/tb/6610 Quinoline yellow Sodium benzoate Carmoisine

15. Alkanes • Alkanes, cannot be named based on their molecular formulas • For example, all of the molecules shown below share the same molecular formula, C6H14(hexacarbon tetradecahydride?) n-hexane 2-methyl-pentane 3-methyl-pentane 2,2-dimethylbutane 2,3-dimethylbutane

16. Alkanes • Organic chemists use a systematic set of rules, called the IUPAC rules, to name organic molecules based on their structural formulas instead of their chemical formulas. n-hexane 2-methyl-pentane 3-methyl-pentane 2,2-dimethylbutane 2,3-dimethylbutane

17. Alkanes • For a discussion on naming alkanes,see the Unit 2Elaboration - Naming Alkanes

18. Constitutional Isomers • When two or more molecules share the same molecular formula, but have different atomic connections, they are called constitutional isomers. n-hexane 2-methyl-pentane 3-methyl-pentane 2,2-dimethylbutane 2,3-dimethylbutane

19. Question (Clicker) • Which of the following is a constitutional isomer of this molecule: A) C) B) D)

20. Conformations • Carbon-carbon single bonds are free to rotate • This leads to different shapes for some molecules • These should not be confused with isomers.

21. Conformations • All of the 3-dimensional models shown below are for the n-butane. • They were generated by rotating the central carbon-carbon bond. • They all share the same structural formula.

22. Conformations • All of the 3-dimensional models shown below are for the n-butane. • They were generated by rotating the central carbon-carbon bond.

23. Conformations • Switching from one conformation to another does not require the breaking and making of covalent bonds. • Switching from one isomer to another does require the breaking and making of covalent bonds. n-butane 2-methylpropane

24. Conformations • For a discussion on conformations,see the Unit 2Elaboration - Conformations

25. Question (Clicker) • True or False? Constitutional isomers have the same IUPAC name. • True • False

26. Question (Clicker) • True or False? The different conformations of an alkane have the same IUPAC name. • True • False

27. Cycloalkanes • When there are three or more carbons in a straight chain, the ends can be joined to make rings. • In naming these molecules, the prefix cyclo- is used to indicate the ring: • Skeletal structural formulas are used to represent the rings in structural formulas:

28. As Parent Chain As Substituent Group Cycloalkanes • In naming these molecules, the prefix cyclo- is used to indicate the ring:

29. Cycloalkanes • The carbon-carbon single bonds for the carbons in a ring are no longer free to rotate. • This leads to a new type of isomer • Since the two structures share the same name, they are not constitutional isomers.

30. Cycloalkanes • Isomers which share the same atomic connections, and therefore, the same IUPAC name are called stereoisomers. • When this occurs due to restricted rotation about a covalent bond, they are called geometric isomers • The prefix cis- and trans- are used to distinguish geometric isomers.

31. Questions • Draw the condensed structural formulas for the following molecules: • 1-ethyl-2-methylcyclopentane • 1,1-dimethylcyclobutane • 1,1-dimethyl-2-propylcyclopropane • Do any of these molecules have cis- and trans- geometric isomers?

32. Alkenes, Alkynes & Aromatic Compounds • The remaining three families of hydrocarbons are unsaturated. • Alkanes are saturated, which means they contain the maximum number of hydrogens per carbon. • For alkanes CnH(2n+2) • Alkenes, Alkynes and Aromatics are unsaturated, which means they contain less than the maximum number of hydrogens per carbon. • Structurally, this means that they have carbon-carbon double or triple bonds

33. Alkenes, Alkynes & Aromatic Compounds • Alkenes are hydrocarbons that contain at least 1 carbon-carbon double bond. • Examples:

34. Alkenes, Alkynes & Aromatic Compounds • Alkynes are hydrocarbons that contain at least 1 carbon-carbon triple bond. • Examples:

35. Alkenes, Alkynes & Aromatic Compounds • Aromatics are unsaturated ring molecules • They are often drawn to look like alkenes, but they behave much differently than alkenes. • They have an alternating pattern of double and single bonds within a ring. • Benzene is an example

36. Alkenes, Alkynes & Aromatic Compounds • The physical properties of all hydrocarbons are the same • The have essentially one noncovalent interaction, which isthe London dispersion force. • They have no electronegative atoms and therefore have • No ion/ion interactions • No dipole/dipole interactions • No hydrogenbonding interactions

37. Alkenes, Alkynes & Aromatic Compounds • Naming of Alkenes and Alkynes work the same as for alkanes, with these added rules: • The parent chain must include both carbons in all double and triple bonds. • Pick the longest chain that also contains all double and triple bonds • The -eneending is used of alkenes • The -yne ending is used for alkynes. • The number of the first carbon in the double or triple bond is included in the name to locate the double or triple bond. • Number the parent chain from the end that is closes to the first double or triple bond.

38. Alkenes, Alkynes & Aromatic Compounds • Naming of Aromatics is based on benzene: • When the molecule is build on benzene, the parent name is “benzene”. • There are also many common names used to describe aromatic compounds.

39. Alkenes, Alkynes & Aromatic Compounds • Naming of Aromatics is based on benzene: • Aromatic compounds can contain multiple aromatic rings

40. Alkenes, Alkynes & Aromatic Compounds • Benzo(a)pyrene found in tobacco smoke is converted to carcinogenic products in the liver (see below) which link to DNA and cause mutations.

41. Practice Quiz 1 KEY • http://www.chem.uwec.edu/Chem150_S07/course/answers/C150-Quiz-1-key.swf

42. Alkenes, Alkynes & Aromatic Compounds • There are many aromatic molecules found in biology • Some aromatic compounds contain nitrogen and oxygen atoms • For example, the nucleotide base Adenine, which is used to make DNA and RNA

43. Alkenes, Alkynes & Aromatic Compounds • Like cycloalkanes, some alkenes can have cis and trans isomers • This is due to restricted rotation about the double-bond. • Not all double bonds produce cis and trans isomers • Each carbon participating in the double bond must have two different substituents attached to them A ≠ B AND X ≠ Y

44. Alkenes, Alkynes & Aromatic Compounds • Like cycloalkanes, some alkenes can have cis and trans isomers

45. Alcohols, Carboxylic Acids & Esters • In addition to the four families of hydrocarbons, there are also many other families of organic molecules. • These other families include elements other than carbon and hydrogen. • They exhibit a wide range of chemical and physical properties. • The families are distinguished by a group of atoms called a functional group

46. Alcohols, Carboxylic Acids & Esters • Functional Group • “A functional group is an atom, group of atoms or bond that gives a molecule a particular set of chemical and physical properties”

47. Alcohols, Carboxylic Acids & Esters • The carbon-carbon double bonds found in alkenes is an example of a functional group. • A chemical property of a double is that it will absorb hydrogen in the hydrogenation reaction.

48. Alcohols, Carboxylic Acids & Esters • We look now at three families that are distinguished by a functional group that contains the element oxygen. • Alcohols • Members of the alcohol family contain a hydroxyl group. • The hydroxyl group comprises an oxygen with one single bond to a hydrogen and another single bond to an alkane-type carbon hydroxyl group An alkane-type carbon atom ethanol

49. + carbonyl group hydroxyl group carboxylic acid group Alcohols, Carboxylic Acids & Esters • We look now at three families that are distinguished by a functional group that contains the element oxygen. • Carboxylic acids • Members of the carboxylic acid family contain a carboxylic acid group • The carboxylic acid group comprises a hydroxyl group connected to a carbonyl group:

50. + carbonyl group hydroxyl group carboxylic acid group Alcohols, Carboxylic Acids & Esters • Carboxylic acids • The present of the hydroxyl group next to the cabonyl group completely changes it properties. • The alcohol hydroxyl group and the carboxylic acid hydroxyl group are chemically quite different, which is why molecules that have the carboxylic acid group are placed in a separate family from the alcohols. • Later in the semester we will learn about some of these chemical differences.