Some Compounds with Oxygen, Sulfur, or a Halogen

Some Compounds with Oxygen, Sulfur, or a Halogen
Chapter 14 Lecture Fundamentals of General, Organic, and Biological Chemistry 8th Edition McMurry, Ballantine, Hoeger, Peterson Chapter Fourteen Some Compounds with Oxygen, Sulfur, or a Halogen Christina A. Johnson University of California, San Diego © 2017 Pearson Education, Inc.

Outline Alcohols, Phenols, and Ethers Naming Alcohols Properties of Alcohols Reactions of Alcohols Phenols Acidity of Alcohols and Phenols Ethers Thiols and Disulfides Halogen-Containing Compounds 14.10 Stereochemistry and Chirality

Outline Concepts to Review Polar Covalent Bonds Section 4.9
Oxidation and Reduction Section 5.5 Hydrogen Bonds Section 8.2 Acid Dissociation Constants Sections 10.6 and 10.7 Functional Groups Section 12.2 Naming Alkanes Section 12.6 Types of Organic Reactions Section 13.5

14.1 Alcohols, Phenols, and Ethers
Outline 14.1 Alcohols, Phenols, and Ethers An alcohol is a compound that has an –OH group bonded to a saturated, alkane-like carbon atom. Learning Objectives: Describe the structural differences between alcohols, phenols, and ethers. Explain why alcohols have higher boiling points than compounds of similar molecular weight (MW).

Outline 14.1 Alcohols, Phenols, and Ethers Phenol is a compound that has an –OH group bonded directly to an aromatic, benzene-like ring. Ether is a compound that has an oxygen atom bonded to two organic groups, R–O–R.

Outline 14.1 Alcohols, Phenols, and Ethers The structural similarity between alcohols and water leads to similarities in physical properties. The high boiling point of ethyl alcohol and water is due to hydrogen bonding.

Outline 14.1 Alcohols, Phenols, and Ethers The high boiling point of water is due to hydrogen bonding. Hydrogen bonds also form between alcohol (or phenol) molecules.

Outline 14.2 Naming Alcohols
Alcohols can have both common and IUPAC names. Learning Objectives: Write systematic names for simple alcohols. Draw the structure of an alcohol given its name, in both condensed and line structure format. Classify an alcohol as primary, secondary, or tertiary. Define and identify a glycol.

Common names of many alcohols containing one hydroxyl (–OH) group identify the alkyl group and then add the word alcohol.

Outline 14.2 Naming Alcohols The International Union of Pure and Applied Chemistry (IUPAC) system names alcohols in a similar manner to that used for alkanes but uses the index number of the hydroxyl (–OH) group and the –ol ending for the parent compound.

STEP 1: Name the parent compound. Find the longest chain that has the hydroxyl substituent attached, and name the chain by replacing the -e ending of the corresponding alkane with -ol.

If the compound is a cyclic alcohol, add the –ol ending to the name of the parent cycloalkane.

STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the hydroxyl group, ignoring the location of other substituents.

In a cyclic alcohol, begin with the carbon that bears the –OH group and proceed in a direction that gives the other substituents the lowest possible numbers.

STEP 3: Write the name, placing the number that locates the hydroxyl group immediately before the compound name. Number all other substituents, and list them alphabetically. In a cyclic alcohol, do not use the number 1 to specify the location of the –OH group.

Outline 14.2 Naming Alcohols

Outline 14.2 Naming Alcohols Dialcohols, or diols, contain two hydroxy groups in the same molecule. The IUPAC names of these alcohols are formed by attaching the ending diol to the alkane name.

The names will contain two numbers indicating the carbons bonded to the two –OH groups, with the numbering starting at the end closest to one of the –OH groups.

Diols with two –OH groups on adjacent carbons are often referred to by the common name glycols. This is preferably reserved for two compounds, ethylene glycol and propylene glycol.

Alcohols are classified as primary, secondary, or tertiary according to the number of carbon substituents bonded to the hydroxyl-bearing carbon.

Outline Worked Example 14.1 Give the systematic name of the following alcohol, and classify it as primary, secondary, or tertiary:

Outline Worked Example 14.1 Cont.
Analysis: First, identify the longest carbon chain, and number the carbon atoms beginning at the end nearer the –OH. The longest chain attached to the –OH has 5 carbon atoms:

Solution: Because the –OH group is bonded to a carbon atom that has three alkyl substituents, this is a tertiary alcohol.

Outline Worked Example 14.2 Draw the structures of: (a) 2,3-dimethyl-2-butanol (b) 3-ethylcyclopentanol Classify each as primary, secondary, or tertiary.

Outline Worked Example 14.2 Cont. Analysis: For both, begin by determining the longest carbon chain; number the carbon atoms and put groups on appropriate atoms. If no index number is given for the –OH group, it is assumed to be on the first carbon.

Outline Worked Example 14.2 Cont. Solution:
The alcohol is a butanol, so it has a longest chain of 4 carbons: Because it is a 2-butanol, the –OH group is bonded to carbon 2; the methyl groups are bonded to carbons 2 and 3:

Outline Worked Example 14.2 Cont. Solution Continued:
(Continued) Filling out the remaining Hs gives us the following (in both condensed and line structure formats): Because the –OH group is bonded to a carbon that has three other carbons bonded to it, this is a tertiary alcohol.

Outline Worked Example 14.2 Cont. Solution Continued:
The name tells us that the –OH group is bonded to a cyclopentane ring; because no position number is given, the –OH group is on carbon 1. Putting in the ethyl group on carbon 3 gives us the following: Because the –OH group is bonded to a carbon atom that has two other carbons bonded to it, this is a secondary alcohol.

14.3 Properties of Alcohols Outline
Alcohols are much more polar than hydrocarbons, which influences the properties of alcohols. Learning Objectives: Describe the properties of alcohols. Describe the hydrophobic and hydrophilic alcohols.

Outline 14.3 Properties of Alcohols Alcohols are polar because of the electronegative oxygen atom. Hydrogen bonding occurs and has a strong influence on alcohol properties.

Outline 14.3 Properties of Alcohols Straight-chain alcohols with up to 12 carbons are liquid. Methanol and ethanol are miscible with water and can dissolve small amounts of ionic compounds. Both are also miscible with many organic solvents.

14.3 Properties of Alcohols
Outline 14.3 Properties of Alcohols All alcohols are composed of a hydrophilic part and a hydrophobic part.

14.3 Properties of Alcohols
Outline 14.3 Properties of Alcohols Alcohols with two or more –OH groups can form more than one hydrogen bond. They are, therefore, higher boiling and more water-soluble than similar alcohols with one –OH group.

14.4 Reactions of Alcohols Alcohols are one of the most important classes of organic molecules because of their versatility in the preparation of other organic molecules. Learning Objectives: Predict the products obtained upon dehydration of an alcohol. Predict the oxidation products of a primary, secondary, and tertiary alcohol.

Outline 14.4 Reactions of Alcohols
Dehydration: Alcohols undergo loss of water on treatment with a strong acid. The reaction is driven to completion by heating. The –OH group is lost from one carbon, and an –H is lost from an adjacent carbon to yield an alkene.

When more than one alkene can result, a mixture of products is formed. The major product has the greater number of alkyl groups directly attached to the double-bond carbons.

Outline Worked Example 14.3
What products would you expect from the following dehydration reaction? Which product will be major and which will be minor?

Analysis: Find the hydrogens on the carbon next to the OH bearing carbon, and rewrite the structure to emphasize these hydrogens:

Outline Worked Example 14.3 Cont. Analysis Continued:
Then, remove the possible combinations of –H and –OH, drawing a double bond where each –H and –OH could be removed: Finally, determine which alkene has the larger number of alkyl substituents on its double-bond carbons and is, therefore, the major product.

Outline Worked Example 14.3 Cont. Solution:

Which alcohol(s) yield 4-methyl-2-hexene on dehydration? Are there any other alkenes that arise from dehydration of these alcohols?

Analysis: The double bond in the alkene is formed by removing –H and –OH from adjacent carbons of the starting alcohol. This removal occurs in two possible ways, depending on which carbon is bonded to the –OH and to the –H.

Solution Continued: Dehydration of 4-methyl-2-hexanol yields 4-methyl-2-hexene as the major product, along with 4-methyl-1-hexene. Dehydration of 4-methyl-3-hexanol yields 4-methyl-2-hexene as the minor product, along with 3-methyl-3-hexene as the major product.

Oxidation occurs when primary and secondary alcohols are converted into carbonyl-containing compounds by an oxidizing agent. A carbonyl group is a carbon attached to an oxygen by a double bond (C=O).

In organic chemistry, a more general definition of oxidation and reduction is used. An organic oxidation is one that increases the number of C–O bonds and/or decreases the number of C–H bonds. An organic reduction is one that decreases the number of C–O bonds and/or increases the number of C–H bonds.

Primary alcohols are converted into aldehydes under controlled conditions, or carboxylic acids, if an excess of oxidant is used.

Secondary alcohols (R2CHOH) are converted into ketones (R2C=O) on treatment with oxidizing agents.

Tertiary alcohols do not normally react with oxidizing agents because they do not have a hydrogen on the carbon atom to which the –OH group is bonded.

What is the product of the following oxidation reaction?

Analysis: The starting material is a primary alcohol, so it will be converted first to an aldehyde and then to a carboxylic acid. To find the structure for these products, first redraw the structure of the starting alcohol to identify the hydrogen atoms on the hydroxyl-bearing carbon:

Outline Worked Example 14.5 Cont. Analysis Continued:
Next, remove two hydrogens, one from the –OH group and one from the hydroxyl-bearing carbon. In their place, make a C=O double bond. This is the aldehyde product that forms initially. Finally, convert the aldehyde to the carboxylic acid by replacing the hydrogen in the –CH=O group with an –OH group.

Outline 14.5 Phenols The word phenol is the name both of a specific compound (hydroxybenzene, C6H5OH), as well as a family of compounds. Learning Objective: Identify a phenol.

Outline 14.5 Phenols Phenol itself, formerly called carbolic acid, is a medical antiseptic that also numbs the skin. It was first used by Joseph Lister, who showed that the instance of postoperative infection dramatically decreased when phenol was used to cleanse the operating room and the patient’s skin. The presence of an alkyl group lowers the absorption through skin, rendering alkyl-substituted phenols less toxic than phenol.

Outline 14.5 Phenols Phenols are usually named with the ending -phenol rather than -benzene.

Outline 14.5 Phenols The properties of phenols are influenced by the electronegative oxygen and hydrogen bonding. Most phenols are somewhat water-soluble and have higher melting and boiling points than similar alkylbenzenes. They are less soluble in water than alcohols.

Outline 14.5 Phenols Many biomolecules contain a hydroxyl-substituted benzene ring.

14.6 Acidity of Alcohols and Phenols
Outline 14.6 Acidity of Alcohols and Phenols Alcohols, such as methanol and ethanol, are about as acidic as water itself. Learning Objective: Explain why alcohols and phenols are weak acids.

Outline 14.6 Acidity of Alcohols and Phenols Alcohols and phenols are very weakly acidic because of the positively polarized –OH hydrogen. They dissociate slightly in solution and establish equilibria between neutral and anionic forms.

Outline 14.6 Acidity of Alcohols and Phenols An alkoxide ion, or anion of an alcohol, is as strong a base as a hydroxide ion. An alkoxide ion is produced by reaction of an alkali metal with an alcohol.

Outline 14.6 Acidity of Alcohols and Phenols Phenols are about 10,000 times more acidic than water. A phenoxide ion is produced by reaction of a phenol with dilute aqueous sodium hydroxide.

Outline 14.7 Ethers The maturation of this silkworm moth is controlled by a hormone that contains a three-membered ether ring. Learning Objectives: Identify an ether. Distinguish between an ether and an alcohol.

Outline 14.7 Ethers Simple ethers are compounds with two organic groups bonded to the same oxygen atom. Ethers are named by identifying the two organic groups and adding the word ether.

Outline 14.7 Ethers Cyclic ethers are often referred to by their common names.

Outline 14.7 Ethers An –OR group is referred to as an alkoxy group.

Outline 14.7 Ethers Ethers do not form hydrogen bonds to one another.
They are higher boiling than alkanes but lower boiling than alcohols. The oxygen atom in ethers can hydrogen bond with water, causing dimethyl ether to be water-soluble and diethyl ether to be partially miscible with water. Ethers make good solvents for reactions where a polar solvent is needed but no –OH groups can be present.

Outline 14.7 Ethers Ethers are alkane-like in many properties and do not react with acids or bases. Simple ethers are highly flammable. On standing in air, many ethers form explosive peroxides, compounds that contain an O–O bond. Ethers must be handled with care and stored in the absence of oxygen. Diethyl ether was a mainstay of the operating room until the 1940s. It acts quickly and is very effective, but has a long recovery time and often induces nausea.

Outline 14.7 Ethers Ethers are found throughout the plant and animal kingdoms. Some are present in plant oils and are used in perfumes; others have a variety of biological roles.

Draw the structure for 3-methoxy-2-butanol.

Analysis: First, identify the parent compound and then add numbered substituents to appropriate carbons in the parent chain.

Solution: The parent compound is a 4-carbon chain with the –OH attached to C2.

Solution Continued: The 3-methoxy substituent indicates that a methoxy group (–OCH3) is attached to C3.

Solution Continued: Finally, add hydrogens until each carbon atom has a total of four bonds.

Outline 14.8 Thiols and Disulfides
Skunks repel predators by releasing several thiols with appalling odors. Learning Objectives: Identify a thiol. Explain how a thiol is converted into a disulfide and vice versa.

Many oxygen-containing compounds have sulfur analogs. Thiols, also called mercaptans, are compounds that contain an –SH group. The systematic name of a thiol is formed by adding -thiol to the parent hydrocarbon name.

Outline 14.8 Thiols and Disulfides The most outstanding characteristic of thiols is their appalling odor. Skunk scent and the odor when garlic and onions are being sliced are thiols. Natural gas is odorless, but methanethiol is added to make leak detection easy.

Thiols react with mild oxidizing agents to yield disulfides. Two thiols join in this reaction, the hydrogen from each is lost, and a bond forms between the sulfurs. The reverse occurs when a disulfide is treated with a reducing agent.

Thiols are important because they occur in the amino acid cysteine, which is part of many proteins. The easy formation of bonds between cysteines helps shape large protein molecules.

The proteins in hair are unusually rich in S–S and S–H groups. Figure Chemistry can curl your hair. A permanent wave results when disulfide bridges are formed between -SH groups in hair protein molecules.

14.9 Halogen-Containing Compounds
Outline 14.9 Halogen-Containing Compounds The simplest halogen-containing compounds are alkyl halides, RX. Learning Objective: Identify an alkyl or aryl halide.

Outline 14.9 Halogen-Containing Compounds The common names of alkyl halides consist of the name of the alkyl group followed by the halogen name with an -ide ending. The compound CH3Br is commonly called methyl bromide.

14.9 Halogen-Containing Compounds
Outline 14.9 Halogen-Containing Compounds The systematic (IUPAC) names of alkyl halides treat the halogen atom as a substituent on a parent alkane. The parent alkane is named in the usual way. The halo-substituent name is then given as a prefix, just as if it were an alkyl group.

Outline 14.9 Halogen-Containing Compounds Aryl halides are compounds that have an aromatic group bonded to a halogen atom, Ar-X.

14.10 Stereochemistry and Chirality
Outline 14.10 Stereochemistry and Chirality Stereochemistry is the study of the relative three-dimensional spatial arrangement of the atoms in a molecule. Learning Objective: Identify a chiral carbon.

Outline 14.10 Stereochemistry and Chirality Stereiosomers: Isomers that have the same molecular and structural formulas but different spatial arrangements of their atoms Configurations: Stereoisomers that cannot be converted into one another by rotation around a single bond

Outline 14.10 Stereochemistry and Chirality The mirror images of your hand cannot be superimposed on each other; one does not completely fit on top of the other. Objects that have handedness in this manner are said to be chiral (pronounced ky-ral, from the Greek cheir, meaning “hand”).

Outline 14.10 Stereochemistry and Chirality Not all objects are chiral. There is no such thing as a right-handed tennis ball or a left-handed coffee mug. Objects that lack handedness are said to be nonchiral, or achiral. Their mirror images are superimposable because they have a plane of symmetry.

Outline 14.10 Stereochemistry and Chirality All that is required for a molecule to be achiral is one plane of symmetry.

Outline 14.10 Stereochemistry and Chirality A chiral carbon atom, or a chiral center, is a carbon atom that is BOTH tetrahedral AND has four different groups attached to it.

Outline 14.10 Stereochemistry and Chirality The two mirror-image forms of a chiral molecule like 2-butanol are called enantiomers or optical isomers (“optical” because of their effect on polarized light). Enantiomers are one kind of stereoisomer. Pairs of enantiomers have many of the same physical properties: the same melting point, solubility in water, isoelectric point, and density.

Outline 14.10 Stereochemistry and Chirality Pairs of enantiomers differ in their effect on polarized light. One enantiomer will rotate the light to the right (and is called the d or (+) enantiomer), and the other will rotate the light to the left (and is called the l or (–) enantiomer).

Outline 14.10 Stereochemistry and Chirality Pairs of enantiomers differ in their biological activity, odors, and tastes.

Outline 14.10 Stereochemistry and Chirality Most importantly, however, pairs of enantiomers often differ in their activity as drugs.

Outline Worked Example 14.7(a)
(a) Glyceraldehyde-3-phosphate is a key intermediate in the metabolism of glucose (both glycolysis and gluconeogenesis). Determine which (if any) of the carbons in this molecule are chiral. (The carbons have been numbered for clarity.)

Worked Example 14.7(a) Cont.
Outline Worked Example 14.7(a) Cont. Analysis: Identify the tetrahedral carbons in the molecule; a carbon will be chiral if it is tetrahedral AND is bonded to four different groups.

Worked Example 14.7(a) Cont.
Outline Worked Example 14.7(a) Cont. Solution: We can ignore Cl, as it is not tetrahedral (carbons that are part of a double bond are trigonal planar). List the groups attached to each of the remaining carbon atoms. Looking at the lists, we see that only carbon 2 has four different groups attached. Therefore, only C2 is chiral.

Outline Worked Example 14.7(b)
(b) 2-Deoxyribose is a carbohydrate that makes up the backbone of the biomolecule ribonucleic acid (RNA). Determine which (if any) of the carbons in this molecule are chiral. (The carbons have been numbered for clarity.)

Worked Example 14.7(b) Cont.
Outline Worked Example 14.7(b) Cont. Analysis: As in part (a), begin by identifying the tetrahedral carbons in the molecule and then list what is attached; use R, R’, and R” to represent different carbon chains when the groups are complex and not as easy to list.

Outline Worked Example 14.7(b) Cont. Solution: When dealing with molecules in line structure format, it is sometimes easier to actually put the carbons in to avoid confusion: All carbons in this molecule are tetrahedral. List the groups attached to each of the remaining carbon atoms.

Outline Worked Example 14.7(b) Cont. Solution Continued: Comparing the groups on each carbon, we see that C2 and C5 are both achiral; note that both have only three different groups attached. The other carbons have four different groups attached. Therefore C1, C3, and C4 are chiral.

Outline Concept Map

Some Compounds with Oxygen, Sulfur, or a Halogen

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