Chem 150 Unit 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 There are three forms of pure carbon Diamond Diamond Graphite Graphite

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

4 Hydrocarbons Organic molecules contain carbon combined with other elements. Organic molecules contain carbon combined with other elements. Organic molecules are grouped into families Organic molecules are grouped into families Members of a family share common structural, physical, and chemical characteristics. Members of a family share common structural, physical, and chemical characteristics. There are four families that contain molecules made of only carbon and hydrogen. There are four families that contain molecules made of only carbon and hydrogen. Hydrocarbons Hydrocarbons Alkanes Alkanes Alkenes Alkenes Alkynes Alkynes Aromatics 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 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. 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 in which the carbons are connected in a straight chain are called normal alkanes. Alkanes that are branched are called branched chain alkanes. Alkanes that are branched are called branched chain alkanes. n-hexanen-hexane 2-methyl-pentane2-methyl-pentane

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

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

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

12 Molecule in the News

13 Molecule in the News:Melamine

Organic Molecules in the News!! Carmoisine Quinoline yellow Sodium benzoate

15 Alkanes, cannot be named based on their molecular formulas For example, all of the molecules shown below share the same molecular formula, C 6 H 14 (hexacarbon tetradecahydride?) For example, all of the molecules shown below share the same molecular formula, C 6 H 14 (hexacarbon tetradecahydride?) Alkanes n-hexanen-hexane 2-methyl-pentane2-methyl-pentane3-methyl-pentane3-methyl-pentane2,2-dimethylbutane2,2-dimethylbutane2,3-dimethylbutane2,3-dimethylbutane

16 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. Alkanes n-hexanen-hexane 2-methyl-pentane2-methyl-pentane3-methyl-pentane3-methyl-pentane2,2-dimethylbutane2,2-dimethylbutane2,3-dimethylbutane2,3-dimethylbutane

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

18 When two or more molecules share the same molecular formula, but have different atomic connections, they are called constitutional isomers. Constitutional Isomers n-hexanen-hexane 2-methyl-pentane2-methyl-pentane3-methyl-pentane3-methyl-pentane2,2-dimethylbutane2,2-dimethylbutane2,3-dimethylbutane2,3-dimethylbutane

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

20 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 were generated by rotating the central carbon-carbon bond. They all share the same structural formula. They all share the same structural formula.

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 were generated by rotating the central carbon-carbon bond.

22 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. Switching from one isomer to another does require the breaking and making of covalent bonds. n-butanen-butane2-methylpropane2-methylpropane

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

24 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: 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: Skeletal structural formulas are used to represent the rings in structural formulas:

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

26 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 This leads to a new type of isomer Since the two structures share the same name, they are not constitutional isomers. Since the two structures share the same name, they are not constitutional isomers. Cycloalkanes

27 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 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. The prefix cis- and trans- are used to distinguish geometric isomers. Cycloalkanes

28 Questions Draw the condensed structural formulas for the following molecules: A)1-ethyl-2-methylcyclopentane B)1,1-dimethylcyclobutane C)1,1-dimethyl-2-propylcyclopropane Do any of these molecules have cis- and trans- geometric isomers?

29 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. Alkanes are saturated, which means they contain the maximum number of hydrogens per carbon. For alkanes C n H (2n+2) For alkanes C n H (2n+2) Alkenes, Alkynes and Aromatics are unsaturated, which means they contain less than the maximum number of hydrogens per carbon. 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 Structurally, this means that they have carbon-carbon double or triple bonds

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

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

32 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 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. They have an alternating pattern of double and single bonds within a ring. Benzene is an example Benzene is an example

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

34 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. 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 Pick the longest chain that also contains all double and triple bonds The -ene ending is used of alkenes The -ene ending is used of alkenes The -yne ending is used for alkynes. 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. 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. Number the parent chain from the end that is closes to the first double or triple bond.

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

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

37 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.

38 Practice Quiz 1 KEY Quiz-1-key.swf Quiz-1-key.swf

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

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

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

42 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. They exhibit a wide range of chemical and physical properties. The families are distinguished by a group of atoms called a functional group The families are distinguished by a group of atoms called a functional group

43 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”

44 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. A chemical property of a double is that it will absorb hydrogen in the hydrogenation reaction.

45 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. 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 The hydroxyl group comprises an oxygen with one single bond to a hydrogen and another single bond to an alkane- type carbon Alcohols, Carboxylic Acids & Esters hydroxyl group An alkane-type carbon atom ethanolethanol

46 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 Members of the carboxylic acid family contain a carboxylic acid group The carboxylic acid group comprises a hydroxyl group connected to a carbonyl group: The carboxylic acid group comprises a hydroxyl group connected to a carbonyl group: Alcohols, Carboxylic Acids & Esters ++ carbonyl group hydroxyl group carboxylic acid group

47 Alcohols, Carboxylic Acids & Esters Carboxylic acids The present of the hydroxyl group next to the cabonyl group completely changes it properties. 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. 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. Later in the semester we will learn about some of these chemical differences. ++ carbonyl group hydroxyl group carboxylic acid group

48 Carboxylic acids The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: Alcohols, Carboxylic Acids & Esters methanoic acid (formic acid) methanoic acid (formic acid) propanoic acid benzoic acid

49 We look now at three families that are distinguished by a functional group that contains the element oxygen. Esters Chemically, esters can be synthesized by reacting a carboxylic acid with and alcohol: Chemically, esters can be synthesized by reacting a carboxylic acid with and alcohol: Alcohols, Carboxylic Acids & Esters carboxylic acid alcoholalcoholesteresterwaterwater

50 We look now at three families that are distinguished by a functional group that contains the element oxygen. Esters Chemically, esters can be synthesize by reacting a carboxylic acid with and alcohol: Chemically, esters can be synthesize by reacting a carboxylic acid with and alcohol: Alcohols, Carboxylic Acids & Esters Ethyl propanoate

51 Carboxylic acids The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: Alcohols, Carboxylic Acids & Esters methanoic acid (formic acid) methanoic acid (formic acid) propanoic acid benzoic acid

52 As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another. With hydrocarbons, there is only one type of noncovalent interaction: With hydrocarbons, there is only one type of noncovalent interaction: Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) The presence of the electronegative oxygen makes alcohols, carboxylic acids and esters polar molecules, these families, therefore, have at least two types of noncovalent interactions: The presence of the electronegative oxygen makes alcohols, carboxylic acids and esters polar molecules, these families, therefore, have at least two types of noncovalent interactions: Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Dipole/Dipole Alcohols, Carboxylic Acids & Esters

53 As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another. Alcohols and Carboxylic acids also have a hydroxyl group with a hydrogen bonded to an oxygen. This allows them to form hydrogen bonds with each other. Therefore, carboxylic acids have at least three different noncovalent interactions: Alcohols and Carboxylic acids also have a hydroxyl group with a hydrogen bonded to an oxygen. This allows them to form hydrogen bonds with each other. Therefore, carboxylic acids have at least three different noncovalent interactions: Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Dipole/Dipole Hydrogen bond Hydrogen bond Alcohols, Carboxylic Acids & Esters

54 To summarize, the types of noncovalent interact ions that each family can participate in include: Hydrocarbons (Alkanes, Alkenes, Alkynes & Aromatics) Hydrocarbons (Alkanes, Alkenes, Alkynes & Aromatics) Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) Esters Esters Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Dipole/Dipole Alcohols & Carboxylic acids Alcohols & Carboxylic acids Induced dipole/Induced dipole (London dispersion force) Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Dipole/Dipole Hydrogen bond Hydrogen bond Alcohols, Carboxylic Acids & Esters

55 These interactions are illustrated in Figure 4.23 of your textbook. Alcohols, Carboxylic Acids & Esters alcoholsalcohols carboxylic acids estersesters

56 Boiling points are a good measure of the strength of the noncovalent interactions between molecules. The stronger the interactions, the higher the boiling point will be. The stronger the interactions, the higher the boiling point will be. Since all molecules have the London dispersion interaction, the boiling points of molecules is expected to increase with temperature. Since all molecules have the London dispersion interaction, the boiling points of molecules is expected to increase with temperature. The next slide shows a chart using the data found in Table 4.7 of Raymond, in which the boiling points for alcohols, carboxylic acids and esters are plotted against molecular weight. The next slide shows a chart using the data found in Table 4.7 of Raymond, in which the boiling points for alcohols, carboxylic acids and esters are plotted against molecular weight. Alcohols, Carboxylic Acids & Esters

57 Alcohols, Carboxylic Acids & Esters As expected, the boiling points for members of all three families increases with molecular weight due to the London dispersion interactions. As expected, the boiling points for members of all three families increases with molecular weight due to the London dispersion interactions. For a given molecular weight, the alcohols and carboxylic acids have a higher boiling point than esters, this is because they can form hydrogen bonds and esters cannot. For a given molecular weight, the alcohols and carboxylic acids have a higher boiling point than esters, this is because they can form hydrogen bonds and esters cannot. The carboxylic acids have a slightly higher boiling point than alcohols, because they can form two hydrogen bonds with a neighboring molecule (See Figure 4.23 in Raymond) The carboxylic acids have a slightly higher boiling point than alcohols, because they can form two hydrogen bonds with a neighboring molecule (See Figure 4.23 in Raymond)See Figure 4.23 in RaymondSee Figure 4.23 in Raymond Molecular Weight {g/mol} Boiling Point {°C}

58 Alcohols, Carboxylic Acids & Esters Another distinguishing characteristic of many of the families is odor. You nose is actually a highly sensitive chemical detector. You nose is actually a highly sensitive chemical detector. The members of different families can interact differently with the receptors in your nose to produce smells that are characteristic of the families they belong to. The members of different families can interact differently with the receptors in your nose to produce smells that are characteristic of the families they belong to. For example: For example: Carboxylic acids produce the pungent, sometime unpleasant odors associated with ripe cheeses, rancid butter and vomit. Carboxylic acids produce the pungent, sometime unpleasant odors associated with ripe cheeses, rancid butter and vomit. Esters, on the other hand, produce the sweet, often pleasant order associated with flowers, perfumes and various natural and artificial flavorings. The next slide shows Figure 4.24 from Raymond, which gives some specific examples. Esters, on the other hand, produce the sweet, often pleasant order associated with flowers, perfumes and various natural and artificial flavorings. The next slide shows Figure 4.24 from Raymond, which gives some specific examples.

59 Examples of some flavorable esters: Alcohols, Carboxylic Acids & Esters

The End