Chapter 22. Organic and Biological Molecules

Chapter 22 Organic and Biological Molecules

The Bonding of Carbon Organic chemistry is the chemistry of compounds containing carbon. Because carbon can form single, double, and triple bonds, the following bonding combinations are possible for carbon: Copyright Cengage Learning. All rights reserved. 23 2

Three types of hydrocarbons exist. Saturated hydrocarbons: contain only carbon carbon single bonds. They may be cyclic or acyclic. Unsaturated hydrocarbons: contain at least one carbon carbon double or triple bonds. Aromatic hydrocarbons: contain benzene rings or similar features. Copyright Cengage Learning. All rights reserved. 23 4

Alkanes and Cycloalkanes Alkanes are acyclic saturated hydrocarbons. Cycloalkanes are cyclic saturated hydrocarbons. The simplest alkane is methane. It can be represented by its molecular formula, CH 4, or by its structural formula: Copyright Cengage Learning. All rights reserved. 23 5

The Alkane Series Alkanes are also called paraffins. They have the general formula C n H 2n+2. This general formula gives no information about how the atoms are connected, however. We will assume that the carbons are bonded together in a straight chain. These compounds are called straight chain or normal alkanes. Copyright Cengage Learning. All rights reserved. 23 7

The structural formulas for the first four alkanes are shown to the right. These alkanes condensed structural formulas are written as follows: Methane: CH 4 Ethane: CH 3 CH 3 Propane: CH 3 CH 2 CH 3 Butane: CH 3 CH 2 CH 2 CH 3 Copyright Cengage Learning. All rights reserved. 23 8

The alkanes constitute a homologous series, a series of compounds in which one compound differs from a preceding one by a fixed group of atoms. Members of a homologous series have similar properties that vary systematically, as shown in Table 23.1. Copyright Cengage Learning. All rights reserved. 23 11

Constitutional Isomerism and Branched Chain Alkanes In addition to straight chain alkanes, branched chain alkanes are possible. Isomers of butane are shown on the next slide. Copyright Cengage Learning. All rights reserved. 23 13

Concept Check 23.1 In the model shown here, C atoms are black and H atoms are light blue. a. Write the molecular formula. b. Write the condensed structural formula. a. C 7 H 16 b. CH 3 CH 2 CH(CH 3 )CH(CH 3 ) 2 Copyright Cengage Learning. All rights reserved. 23 17

Sources of Alkanes and Cycloalkanes Petroleum, or crude oil, is a mixture of alkanes and cycloalkanes with small amount of aromatic hydrocarbons. Crude oil from different regions differ in their compositions of these compounds. Copyright Cengage Learning. All rights reserved. 23 20

Oil from the Canadian north slope contain molecules composed of 20 to 40 carbon atoms. Oil from Saudi Arabia contain molecules composed of 5 to 20 carbon atoms. This oil is more desirable as a source because it is easier to transport crude oil containing low molecular mass molecules. Hydrocarbon mixtures in crude oil are separated by a process known as fractional distillation. This process separates molecules according to molecular mass. Copyright Cengage Learning. All rights reserved. 23 21

Alkenes and Alkynes Alkenes and alkynes are unsaturated hydrocarbons. Alkenes contain carbon carbon double bonds. They have the general formula C n H 2n. Alkynes contain carbon carbon triple bonds. They have the general formula C n H 2n 2. Copyright Cengage Learning. All rights reserved. 23 22

Alkenes and Geometric Isomers In an alkene, all of the atoms connected to the double bonded carbons are in one plane. Rotation around the carbon carbon double bond is restricted due to the side to side overlap of the p orbitals to form the p bond. This makes geometric isomers that is, cis and trans isomers possible. Copyright Cengage Learning. All rights reserved. 23 23

Alkynes Alkynes are unsaturated hydrocarbons containing a carbon carbon triple bond. The general formula is C n H 2n 2. The simplest alkyne is acetylene, C 2 H 2. It is very reactive with oxygen, so it is used in torches for welding to give a very hot flame (~3000 C). Copyright Cengage Learning. All rights reserved. 23 25

Naming Hydrocarbons 1. Determine the longest continuous chain of carbon atoms. 2. Name any chain branching off of the longest chain as an alkyl. 3. Locate the branch on the longest chain by counting the carbon to which it is attached so that it has the lowest number possible. 4. For more than one of a group, use prefixes. Copyright Cengage Learning. All rights reserved. 23 27

? Write the condensed structural formula of 2,3,5 trimethylhexane. Hexane is a six carbon chain. 2,3,5 Trimethyl means three methyl groups: one each at the 2, 3, and 5 carbons. Copyright Cengage Learning. All rights reserved. 23 29

IUPAC Rules for Naming Alkenes and Alkynes Identify the longest chain containing the multiple bonds. Alkenes have contain carbon carbon double bond(s) and alkynes contain carbon carbon triple bond(s). The longest chain provides the stem name followed by the ending ene for alkenes or yne for alkynes. Copyright Cengage Learning. All rights reserved. 23 30

Number the longest chain from the end neared the multiple bond. The multiple bond is given the number of the first carbon atom involved in the multiple bond. This number is written in front of the alkene or alkyne name, separating the number from the name by a dash. Branched chains are named using the same method used in naming alkanes. If the multiple bond is in the middle of the longest chain, number the chain from the end that gives the branches the lowest number. Copyright Cengage Learning. All rights reserved. 23 31

The simplest alkene, CH 2 CH 2, is ethene and has a common name of ethylene. The simplest alkyne, CHCH, is ethyne and has a common name of acetylene. Copyright Cengage Learning. All rights reserved. 23 32

Concept Check 23.3 In the model shown here, C atoms are black and H atoms are light blue. a. Write the molecular formula. b. Write the condensed structural formula. c. Write the IUPAC name. a. C 5 H 10 b. CH 3 CH=CHCH 2 CH 3 c. 2 pentene Copyright Cengage Learning. All rights reserved. 23 33

Aromatic Hydrocarbons Aromatic hydrocarbons usually contain benzene rings: six membered rings of carbon atoms with alternating carbon carbon single and carbon carbon double bonds. The molecular orbital description of benzene utilizes a p molecular orbital that is delocalized across the entire molecule. The result is that the double bonds in benzene do not behave as isolated double bonds. Copyright Cengage Learning. All rights reserved. 23 36

Some polycyclic aromatic hydrocarbons are shown on the next slide. Naphthalene is the simplest member of the series. This white, crystalline substance is used in manufacturing plastics and plasticizers (to keep plastic pliable). Small amounts are used for mothballs. Copyright Cengage Learning. All rights reserved. 23 39

The term aromatic indicates that compounds containing a benzene ring have aromas. Flavoring agents that can be made in the lab or are found in nature and that contain benzene rings include cinnamaldehyde, which is the source of the cinnamon flavor, and methyl salicylate, which is the source of the wintergreen flavor that is used in candies and gum. Benzene rings are also found in pain relievers such as acetylsalicylic acid (aspirin), acetaminophen (Tylenol), and the illegal drug mescaline. Copyright Cengage Learning. All rights reserved. 23 41

Nomenclature of Aromatic Hydrocarbons Simple benzene compounds have one group substituted on the benzene ring. They are named by using the attached group name as the prefix. For example, this compound is ethylbenzene: Copyright Cengage Learning. All rights reserved. 23 43

When two groups are on the benzene ring, the three are isomers are named by the relative position of the two groups. The following three isomers are called ortho dimethylbenzene or o xylene (left); meta dimethylbenzene or m xylene (center); and para dimethylbenzene or p xylene (right). Copyright Cengage Learning. All rights reserved. 23 44

1 ethyl 3 methylbenzene Numbers are also used to show the positions of two or more groups so that they have the lowest possible numbering. 1,3,5 trimethylbenzene Copyright Cengage Learning. All rights reserved. 23 45

Derivatives of Hydrocarbons Certain groups of atoms in organic molecules are especially reactive and have characteristic chemical properties. A functional group is a reactive portion of a molecule that undergoes predictable reactions. Table 23.7 lists some common functional groups. Copyright Cengage Learning. All rights reserved. 23 47

Alcohols and Ethers We can think of an alcohol as a compound obtained by substituting a hydroxyl group ( OH) for a hydrogen atom ( H) on a tetrahedral (sp 3 hybridized) carbon atom of a hydrocarbon group. Alcohols are named by IUPAC rules similar to those for naming the hydrocarbons, except the stem name is the longest chain that contains the OH group and the name ends with the suffix ol. Copyright Cengage Learning. All rights reserved. 23 50

Common Names of Ethers Ethers have common names formed from the hydrocarbon groups followed by the word ether. The hydrocarbon groups are listed alphabetically. For example, CH 3 OCH 2 CH 2 CH 3, has a common name of methyl propyl ether. Copyright Cengage Learning. All rights reserved. 23 52

Alcohols are classified according to the number of carbon atoms attached to the carbon with the hydroxyl group. A primary alcohol has only one other carbon bonded to the hydroxyl carbon. A secondary alcohol has two other carbons bonded to the hydroxyl carbon. A tertiary alcohol has three other carbons bonded to the hydroxyl carbon. Copyright Cengage Learning. All rights reserved. 23 54

An ether can be thought of as a derivative of an alcohol in which the hydrogen of the hydroxyl group is replaced with an alkyl group. Hydrocarbon groups are symbolized by using the letter R. R O H An alcohol R O R An ether Copyright Cengage Learning. All rights reserved. 23 55

Aldehydes and Ketones A carbonyl group is composed of a carbon oxygen double bond (right). An aldehyde is a compound that contains a carbonyl group with at least one hydrogen attached to it. A ketone is a compound containing a carbonyl group with two hydrocarbons attached to it. Copyright Cengage Learning. All rights reserved. 23 56

Some Aldehydes of Aromatic Hydrocarbons Note: there is also an alcohol and ether group. Benzaldehyde (oil of almond) Vanillin (extract of vanilla) Cinnamaldehyde (oil of cinnamon) Copyright Cengage Learning. All rights reserved. 23 57

Carboxylic Acids and Esters A carboxylic acid is a compound that contains the carboxyl group, COOH. An ester is a derivative of a carboxylic acid in which the hydrogen of the carboxyl group is replaced with an alkyl group. The ester, RCOOR, is formed from the reaction of a carboxylic acid, RCOOH, and an alcohol, R OH. Copyright Cengage Learning. All rights reserved. 23 58

IUPAC Names for Carboxylic Acids and Esters Carboxylic acids are named by IUPAC rules like those for aldehydes, except the ending on the stem name is oic followed by the word acid. For example, the structure below is ethanoic acid. Copyright Cengage Learning. All rights reserved. 23 59

Organic Compounds Containing Nitrogen Most organic bases are amines that is, compounds structurally derived by replacing one or more of the hydrogen atoms of ammonia with hydrocarbon groups. A primary amine has replaced one hydrogen. A secondary amine has replaced two hydrogens. A tertiary amine has replaced all three hydrogens. Amines act as Brønsted Lowry bases by accepting a proton from water, producing a derivative of an ammonium ion and the hydroxide ion. Copyright Cengage Learning. All rights reserved. 23 61