Chapter Fourteen

Organic Compounds With Oxygen, Sulfur, or a Halogen

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What you will learn

1. structures and uses of alcohols, phenols, ethers, thiols, and alkyl halides

2. Writing systematic names structures3. Describing properties (polarity, hydrogen bonding, and

water solubility).4. Understanding the slightly acidic nature of alcohols and

phenols5. Predicting the products of the dehydration of alcohols 6. Predicting products of oxidation of alcohols and thiols

Alcohols, Phenols, and Ethers

Alcohol has an –OH bonded to an alkyl group

R-OH

Ether has an O bonded to two organic groups, it is an oxygen “bridge” between R groups

R-O-R

Phenol has an –OH bonded directly to an aromatic ring

R =

Hydrogen bonding

• the bond is very polar, • Strong intermolecular

forces exist.

• When hydrogen is bound to an electronegative atom (oxygen, nitrogen fluorine or chlorine),

• High boiling point

• Low vapor pressure

Alcohols have hydrogen bonding

The high boiling point of Ethyl alcohol (and water), is due to hydrogen bonding.

Do Ethers Have Hydrogen Bonding?

1 2 3

33% 33%33%

1. Yes2. No3. Depends

on what ether

Do Ethers Have Hydrogen Bonding?

1. No2. No

hydrogen's are bound to oxygen

Ethers have a hydrogen, but not as part of a hydroxyl group – they cannot form hydrogen bonds.

As a result, they have lower boiling points. Ethers, in fact, resemble alkanes in many of their properties.

Do Phenols Have Hydrogen Bonding?

1 2 3

33% 33%33%

1. Yes2. No3. Depends on

what phenol

Water (HOH) is

1. An acid2. A base3. An amphoteric substance

For an alcohol or phenol to act as an acid – it must give up the H bound to oxygen.

While alcohols will act as an acid if in the presence of a STRONG base, The phenol is much more capable of acting as an acid

Functional Groups with Oxygen

• When hydrogen is bound to oxygen:– expect hydrogen bonding, – high boiling point– Expect some ability to act as an acid

• Ability to act as a acid also depends on the ability to “share” a delocalized charge

The More Charge Sharing – the more reactive

• Ability to act as a acid also depends on the ability to “share” a delocalized charge

1o

2o

3o

• The high boiling point of Ethyl alcohol (and water), is due to hydrogen bonding.

• Alkanes lack the electronegative oxygen, and do not have hydrogen bonding

• Ethers have a hydrogen, but not as part of a hydroxyl group – they cannot form hydrogen bonds.– As a result, they have lower boiling points. Ethers, in

fact, resemble alkanes in many of their properties.

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Common Alcohols

1. Simple alcohols : solvents, antifreeze agents, and disinfectants – They are involved in the metabolic processes of all

living organisms.2. Methyl alcohol is commonly known as wood

alcohol –Once prepared by heating wood in the absence

of air

Ethyl Alcohol

• Ethyl alcohol; or ethanol is produced by fermentation, and is called “grain alcohol”, or “denatured alcohol”. – Gasohol is a blend of ethyl

alcohol and gasoline Fermentation of grain and sugar.

• All table wines and beers, and distilled liquors

• Isopropyl alcohol, or rubbing alcohol, is used for rubdowns, as a solvent, or to sterilize for instruments– Less toxic than methyl alcohol,

isopropyl alcohol is more toxic than ethyl alcohol.

Toxicity

Diols – have two hydroxyl groups

• Ethylene glycol: a toxic, colorless liquid,

• miscible with water– used as antifreeze and

as a material for making polyester

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Triol’s: Three hydroxyl groups

• Glycerol (glycerin) triol• sweetener,• moisturizer, • plastics manufacture,• Antifreeze & shock-

absorber fluids

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Naming AlcoholsSTEP 1: Name the parent compound. 1. Find the longest chain that has the hydroxyl

substituent attached.2. name the chain by replacing the –e ending of the

corresponding alkane with -ol:

Name as hexanol: it has a six carbon chain containing the hydroxyl group

STEP 2: Number the carbon atoms in the main chain.

• Begin at the end nearer the hydroxyl group, – If the compound is a cyclic alcohol, add the -ol ending

to the name of the parent cycloalkane.– In a cyclic alcohol, begin with the carbon that bears

the –OH group and proceed in a direction that gives the other substitutes the lowest possible numbers.

.STEP 3: Write the name,1. place the number that locates the hydroxyl group immediately

before the parent compound name.2. Number the positions of all other substituents, and list them

alphabetically. Note that in a cyclic alcohol, it is not necessary to use the number “1” to specify the location of the –OH group

5-Methyl-3-hexanol

Note that in a cyclic alcohol, it is not necessary to use the number “1” to specify the location of the –OH group

• Dialcohols, or diols, are often called glycols.– Ethylene glycol is the simplest glycol; propylene glycol is

often used as a solvent for medicines that need to be inhaled or rubbed onto the skin.

• Numbering starts from the end closer to an –OH group, and the -diol name ending is used.

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

• one substituent primary, • Two substituents secondary• three substituents tertiary.

Chapter Fourteen 25Copyright © 2010 Pearson Education, Inc.

14.4 Properties of Alcohols• Alcohols are much more polar than hydrocarbons.

Hydrogen bonding also occurs and has a strong influence on alcohol properties.

• Straight-chain alcohols with up to 12 C’s are liquids, and each boils at a considerably higher temperature than the related alkane.

• Alcohols with a small organic part resemble water. Methanol and ethanol are miscible with water and they can dissolve small amounts of many salts.

• Alcohols with a large organic part are more like alkanes. 1-Heptanol is nearly insoluble in water and can’t dissolve salts but does dissolve alkanes.

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Alcohols with 2 or more –OH groups can form more than one hydrogen bond. They are higher boiling and more water soluble than similar alcohols with one –OH group.

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Reactions of Alcohols

• Alcohols undergo loss of water (dehydration) on treatment with a strong acid catalyst.

• An alkene and water are produced

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• When more than one alkene can result from dehydration of an alcohol, a mixture of products is usually formed.

• The major product has the greater number of alkyl groups attached to the double-bond carbons.

• Primary and secondary alcohols are converted into carbonyl-containing compounds on treatment with an oxidizing agent. – A carbonyl group is a functional group that has a C=O.

The symbol [O] will indicate a generalized oxidizing agent.• An organic oxidation is one that increases the

number of C-O bonds and/or decreases the number of C-H bonds.

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

Secondary alcohols are converted into ketones 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.

Phenols• Phenol is the name both of a specific compound,

hydroxybenzene, and of a family of compounds. • Phenols are usually named with the ending -phenol

rather than -benzene even though their structures include a benzene ring.

• Phenol is a medical antiseptic first used by Joseph Lister in 1867. – Lister showed that the occurrence of postoperative

infection dramatically decreased when phenol was used to cleanse the operating room and the patient’s skin.

– Many mouthwashes and throat lozenges contain alkyl-substituted phenols such as thymol as active ingredients for pain relief.

• Alkyl-phenols are disinfectants in hospitals. (Antiseptics safely kill microorganisms on living tissue, disinfectants should only be used on inanimate objects).

Acidity of Alcohols and PhenolsAlcohols and phenols are weakly acidic. – They dissociate slightly in water and establish

equilibrium between neutral and anionic forms:

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• Methanol and ethanol are about as acidic as water, with Ka 10-15 .Their aqueous solutions are neutral.

• An anion of an alcohol, is as strong a base as hydroxide ion.

• Phenols are considerably more acidic than water,• Phenol itself has Ka = 1.010-10

Why is phenol basic?

• The aromatic ring has a great deal of stability due to resonance this leads to a delocalization of charge

The general rule-of-thumb is that if a charge is very localised (all concentrated on one atom) the ion is much less stable than if the charge is spread out over several atoms

Ethers

Ethers are named by identifying the two organic groups and adding the word ether.

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Cyclic Ethers

• Compounds that contain the oxygen atom in a ring are classified as cyclic ethers

• They are often given common names

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Alkoxy GroupOrganic compounds will often have more than one functional group. When the ether group (an oxygen bridge) is present the compound is named as an alkoxy, using the name of the R group.

-OCH2CH3 is an ethoxy group

Alkoxy Group

OCH3 is a methoxy group; so this compound is either ortho methoxyphenol, or 2-methoxyphenol

Recall that the benzene ring is challed a phenol group

Properties of Ethers

1. Polar, but not enough to form hydrogen bonds – so , a much lower boiling point and lower vapor point than alcohols

2. The polarity leads to moderate solubility, the larger the R group – the less soluble in water

3. The simple ethers are highly flammable. On standing in air, many ethers form explosive peroxides, compounds that contain an O-O bond

Thiols and DisulfidesThiols are sulfur analogs of alcohols. 1. The systematic name of a thiol is

formed by adding -thiol to the parent name.

2. Skunk scent is caused by the two thiols shown below

1. Thiols (R-SH) react with mild oxidizing agents to yield a disulfide (R-S-S-R).

2. The reverse reaction (R-S-S-R 2R-SH) occurs when a disulfide is treated with a reducing agent.• Hair protein is rich in S-S and –SH groups. When hair is

‘permed’ some disulfide bonds are broken and new ones are formed giving hair a different shape.

The Alkyl Halides:Halogen Containing Compounds

1. R, bonded to a halogen, X (R-X)2. Common names consist of the alkyl group

followed by the halogen name with an -ide ending.

3. Systematic names consider the halogen atom as a substituent on a parent alkane.

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• Halogenated organic compounds have a variety of medical and industrial uses:

-Anesthetics-Solvents, Propellants, Degreasing agents-Fire extinguishers-Herbicides, Fungicides, Insecticides

• Despite the enormous benefits of halogenated organic compounds, their use has been restricted, and sometimes banned altogether because:

-They persist in the environment and are not broken down rapidly. -They accumulate in some animals to

harmful levels.-They can damage the ozone layer.

Halogen Compounds: KI• Halogen-containing organic compounds are important

in marine organisms, few are significant in human biochemistry.

– One exception is thyroxine, an iodine-containing hormone secreted by the thyroid gland.

A deficiency of iodine in the diet leads to a low thyroxine level, which causes a swelling of the thyroid gland called goiter. To ensure adequate iodine in the diet KI is sometimes added to table salt.

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Chapter Summary• An alcohol has an –OH group bonded to a saturated,

alkane-like carbon atom; a phenol has an –OH group bonded directly to an aromatic ring; and an ether has an oxygen atom bonded to two organic groups.

• Phenols are notable for their use as disinfectants and antiseptics; ethers are used primarily as solvents.

• Thiols are sulfur analogs of alcohols, with unpleasant odors. Thiols are found in proteins.

• Alkyl halides contain a halogen atom bonded to an alkyl group. Halogenated compounds are widely used in industry as solvents and in agriculture as herbicides, fungicides, and insecticides.

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Chapter Summary Contd.

• Alcohols are named using the -ol ending, and phenols are named using the -phenol ending. Ethers are named by identifying the two organic groups attached to oxygen, followed by the word ether. Thiols use the name ending -thiol, and alkyl halides are named as halo-substituted alkanes.

• Both alcohols and phenols are like water in their ability to form hydrogen bonds. As the size of the organic part increases, alcohols become less soluble in water. Ethers do not hydrogen-bond and are more alkane-like in their properties.

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Chapter Summary Contd.

• Alcohols and phenols are weak acids that can donate H+ to a strong base. Alcohols and water have similar acidity; phenols are more acidic than water.

• Alcohols dehydrate to yield alkenes when treated with a strong acid, and they undergo oxidation to yield compounds that contain a carbonyl group. Primary alcohols are oxidized to yield either aldehydes or carboxylic acids, secondary alcohols are oxidized to yield ketones and tertiary alcohols are not oxidized.

• Thiols react with mild oxidizing agents to yield disulfides (RSSR), a reaction of importance in protein chemistry. Disulfides can be reduced back to thiols.