Hydrogen bonds These require both positive hydrogens · PDF file-Hydrogen bonds These require both positive hydrogens ... have lower densities and lower boiling points ... Chapter

Copyright © Houghton Mifflin Company. All rights reserved. 13–1

The Rules for Boiling Points

• The boiling points of compounds depend on how strongly they stick together: The more strongly they stick together, the higher the boilingpoint (the more heat it takes to rip them apart).

• There are two main forces that hold molecules together:-Hydrogen bonds

These require both positive hydrogens (from O-H or N-H bonds) and electron lone pairs (found mainly on O and N atoms)

-London forces (see Chapter 6, pages 169-170)-Bigger molecules have stronger intermolecular forces, and higherboiling points, other things being equal.-These forces are very short-range, so this also depends on how close the molecules can get together. The more branches in an alkane, the harder it is for them to get close. Branched alkanes thus have lower densities and lower boiling points (see page 257).


Recent NewsRecent News

• A recent report asserts that dogs have been trained to detect cancer by sniffing samples taken from the breaths of healthy persons and cancer victims.

• Dogs can detect odors at the low parts per billion (ppb) level.

• It is claimed that tumor cells emit different chemicals--alkanes and benzene derivatives--than healthy cells.

• Reference: The New York Times, January 17, 2006, p. D5.


ADVICE

• It is very important that you begin to study the material as early as possible.

• Working the practice problems and answering the practice questions is absolutely essential.

Chapter Thirteen

Hydrocarbon Derivatives II:

Carbon Oxygen Double Bonds


Functional Groups Containing the Carbon-Oxygen Double Bond


13.1 The Carbonyl Group

• A Carbonyl Group consists of a carbon atom and an oxygen atom joined by a double bond. This is by definition a carbonyl group (C=O).

» Acetone for example contains a carbonyl group.

• Carbonyl groups are strongly polarized, with a partial positive charge on carbon and partial negative charge on oxygen.

H3C CH3

O

Pronounced carbon-EEL


Because oxygen is more electronegative than carbon,it pulls the electrons in the double bond toward oxygencreating a partial negative charge on oxygen and a partialpositive charge on the carbonyl carbon atom. Much of the reactivity of carbonyl groups results from this polarization.

E.N. = 3.5

E.N. = 2.5


• The polarity of the carbonyl group contributes to its reactivity.

• The carbonyl carbon is bonded to oxygen and two other atoms. The bond angles between the three components on carbon are 120o or close to it.

• Carbonyl compounds are broadly divided into two groups: (1) aldehydesand ketones are in one group and (2) the second group contains carboxylic acids, esters, and amides.



Structural Characteristics and Naming of Aldehydes


An aldehyde is a compound that has at least onehydrogen atom attached to the carbon atom of acarbonyl group.

H

O

CH 3

O

an aldehyde a ketone

R H

OThe R group in an aldehyde can beH, alkyl, or aryl.


Some Common Aldehydes

• Formaldehyde, H(C=O)H: Toxic but useful. It kills viruses, fungi, and bacteria. It is used in disinfecting and sterilizing equipment.

• Acetaldehyde CH3(C=O)H: Sweet smelling and narcotic. Present in ripe fruits, especially in apples. It is less toxic than formaldehyde.

• Benzaldehyde Ph(C=O)H: Oil of almonds; used to make dyes, perfumes, and specific flavors.


H

OH

O

OHO

CH3

H

HO

H

oil of almonds cinnamaldehyde vanillin

Some Common Aldehydes

Some aldehydes are present in nuts and spices.


Naming Aldehydes

The simplest aldehydes are known by their common names, formaldehyde, acetaldehyde, benzaldehyde, and so on. To name aldehydes systematically in the IUPAC system, the final –e of the name of the alkane is replaced by –al.


When a compound contains more than one type offunctional group, the suffix for only one of them canbe used as the ending of the name. The IUPAC rulesdefine priorities that specify which suffix should beused:

1. Carboxylic acid2. Aldehyde3. Ketone4. Alcohol5. Amine6. Alkene7. alkyne

Remember that alkoxy (ether), halogen (halide), and alkylGroups are treated as substituents and listed in alphabetical order.


1. To name an aldehyde, select the longest chain whichcontains the aldehyde functional group.2. Then name the parent chain by changing the -e endingto -al.3. Number the parent chain starting with 1 for the aldehydecarbon atom.4. Determine the identity of the substituents, and add thisinformation to the front of the parent chain name.

H

OOH

pentane pentanal

pentanal 3-hydroxypentanal

Note that the aldehydeis the primary functionalgroup and so this isnamed as an aldehyde andnot as an alcohol.


Properties and Reactions of Aldehydes


Properties of Aldehydes and Ketones

• The polarity of the carbonyl group makes aldehydes and ketones moderately polar compounds. As a result, they have boiling points higher than alkanes and are reactive.

• Aldehydes and ketones do not form hydrogen bonds to each other, however, they form hydrogen bonds with water using the lone pairs of electrons on oxygen.

• Aldehydes and ketones have boiling points intermediate between alkanes and alcohols of similar size.


Aldehydes and ketones are soluble in common organic solvents, and those with fewer then five carbons are also soluble in water.


Rules for Solubility• “Like dissolves like.” This means that polar compounds dissolve best in polar solvents (like water and alcohols) and nonpolarcompounds dissolve best in nonploar solvents (like hexane and benzene).

• Some compounds, like alcohols, have a polar part (the -OH group) and a nonpolar part (the hydrocarbon portion). Solubility in water depends on which part dominates. Alcohols with a large “organic” (hydrocarbons) portion are not very soluble in water.

• Carbonyl compounds will be soluble in water if their hydrocarbon portion is not too large. The water can form hydrogen bonds to the electron lone pairs on the oxygen. But if the organic portion is too large, solubility is decreased.

• Acetone, CH3-(C=O)-CH3, is an excellent solvent for both polar and nonpolar compounds.


--Simple ketones are excellent solvents because they dissolve both polar and nonpolar compounds; acetone(CH3HC=O) is an example.--The lower boiling aldehydes and ketones are flammable.--The simple ketones have low toxicity, however, many simple aldehydes are toxicbecause they react with proteins and otherbiomolecules; example -formaldehyde.


Oxidation of Aldehydes

• Primary alcohols can be oxidized to aldehydes and secondary alcohols to ketones.

• Aldehydes can be further oxidized to carboxylic acids.

• Since ketones cannot be further oxidized, application with a mild oxidizing agent can be used as a test to distinguish between aldehydes and ketone.


Primary alcohol:

CH3CH2OH + [O] → CH3CH=O + H2O [oxidation to analdehyde]

CH3CH=O + [O] → CH3COOH + H2O [further oxidationto an organic acid]

Secondary alcohol:OH [oxidation to a| ketone]

CH3CH-CH3 + [O] → CH3(C=O)CH3 + H2O

The ketone cannot be further oxidized.


A positive Tollens test for aldehydes involves the formation of a silver mirror. (a) An aqueous solution of ethanal is added to a solution of silver nitrate in aqueous ammonia and stirred. (b) The solution darkens as ethanal is oxidized to ethanoic acid, and Ag+1 ion is reduced to silver. (c) The inside of the beaker becomes coated with metallic silver.

Tollens test: Ag+ (soluble) Ag metal (mirror).

The aldehyde is oxidized and the metal is reduced.


Benedict’s solution, which is blue in color, turns brick red when an aldehyde reacts with it.

Benedict’s test: Cu++ (blue) Cu+ (brick red).

The aldehyde is oxidized andthe metal is reduced.


Reduction of Aldehydes and Ketones

• Reduction is the reverse of the oxidation reaction. Reduction of a carbonyl group is the addition of hydrogens across the double bond to produce an –OH group.

• Aldehydes are reduced to primary alcohols, and ketones are reduced to secondary alcohols.

• Reduction of the carbonyl group occurs by formation of a bond to the carbonyl carbon by a hydride, H:-, ion accompanied by bonding of a H+ ion to the carbonyl oxygen atom.


Structural Characteristics and Naming of Ketones


Acetone, CH3(C=O)CH3): It is one of the most widely used solvents. It can dissolve most organic compounds and is also miscible with water. Acetone is highly volatile and is also highly flammable. Ketones, like aldehydes, occur widely in Nature.

OO

2-heptanonecloves

carvonespearmint flavoring


• Some ketones are best known by their common names which give the names of the two alkyl groups bonded to the carbonyl group followed by the word ketone. For example, ethyl methyl ketone =

CH3-(C=O)-CH2-CH3

• Ketones are named systematically (IUPAC) by replacing the final –e of the corresponding alkane name with –one. The numbering of the alkane chain begins at the end nearest to the carbonyl group. The location of the carbonyl group is indicated by placing the number of the carbonyl carbon in front of the name; e.g. 2-propanone = acetone. The above compound is … 2-butanone


Properties and Reactions of Ketones


The physical properties of ketones closely parallelthe properties of aldehydes; i.e. their boiling pointsare intermediate between alkanes and alcohols.

Ketones are not readily oxidized.

Ketones are readily reduced to secondary alcohols.O

H 2

N i c a ta ly s t

O H


Chemistry at a Glance:Reactions Involving Aldehydes and Ketones


Carboxylic Acids


Carboxylic Acids and Their Derivatives: Properties and Names

• Caboxylic acids have an –OH group bonded to a carbonyl group. In their derivatives, OH is substituted by other groups. Such as,Esters have an –OR group bonded to a carbonyl group. Amides have an –NH2 group bonded to a carbonyl group.


Carboxylic Acidsare acidic

• Carboxylic acids donate a proton to bases.

• Carboxylic acids hydrogen bond with each other. As a result of hydrogen bonding, they have higher boiling points than similar alkanes.


Learn these names


Two common NSAID’s (non-steroidal anti-inflammatorydrugs) are Ibuprofen (a.k.a. Motrin and Advil) andNaproxen (a.k.a. Naprosyn and Aleve). They are bothcarboxylic acids.

CO2H CO2H

O

ibuprofen naproxen

Chronic long term used of these OTC drugs has recentlybeen shown to increase the risk of heart disease.


Advil and Aleve


--Carboxylic acids have a sharp and strong odor.--Up to four carbon containing carboxylic acids are water soluble.--Carboxylic acids are named systematically (IUPAC) by replacing the –e at the end of the alkane name with – oic acid. If alkyl or other substituents are present, the chain is numbered beginning at the COOH end.


O H

O O

Carboxylic acids have a higher priority when naming.Therefore, this molecule is not named as a ketone, butinstead is named as a carboxylic acid.

5-oxohexanoic acid

O

O H

2-ethyl-5-methylbenzoic acid


Dicarboxylic acids, which contain two –COOH groups, include the biochemicalssuccinic acid, HOOC-CH2-CH2-COOH, and glutaric acid, HOOC-CH2-CH2-CH2-COOH.

Unsaturated acids are named systematically in the IUPAC system with the ending –enoic acid.

Acids with larger saturated alkyl groups are waxy, odorless solids.

Water solubility decreases as the size of the alkyl group increases.


Chemical Portraits:Commonly Encountered Carboxylic Acids


Properties and Reactions of Carboxylic Acids


Notes on Some Common Carboxylic Acids

• Formic acid, HCOOH: Chemical that is present in the sting of ants.

• Acetic acid, CH3COOH: dilute (5%) aqueous acetic acid is known as vinegar.

• Butyric acid, CH3CH2CH2COOH: Chemical responsible for odor of rancid butter.

• Amino acids, the building blocks of proteins, have the general formula R-CH(NH2)-COOH.

• Citric acid: Present in citrus fruits and blood.


Acidity of Carboxylic Acids

• Carboxylic acids are weak acids.• Acid strengths of common carboxylic

acids are about the same as that for acetic acid.

• Carboxylic acids undergo neutralization reactions with bases and produce water and a carboxylic acid salt.

• The sodium and potassium salts of carboxylic acids are ionic solids that are more soluble in water than the carboxylic acids themselves.


Carboxylic acids are acids because they donatea proton to a base; e.g. water.

OH

O+ H

OH O

O+ H3O+

carboxylate ion

hydronium ion

A carboxylate ion is a negative ion produced when acarboxylic acid loses a proton (acidic hydrogen atom).In this case the equilibrium lies far to the left becausecarboxylic acids are weak acids and therefore do notcompletely ionize.

butyric acid


A given carboxylic acid molecule can form two hydrogen bonds to another carboxylic acid molecule, producing a “dimer.” Dimers have twice the mass of a single molecule, and a higher temperature is needed to boil carboxylic acids than would be needed if no

dimers were present.


The boiling points of monocarboxylic acids compared to those of other types of compounds. All compounds in the comparison have unbranched carbon chains.


The solubility of saturated unbranched-chain carboxylic acids decreases as carbon-chain length increases.


OH

O+

O

O+ H2ONaOH Na+

HCl+ NaCl

Carboxylic acids react completely with strong basessuch as NaOH. The resulting carboxylate salts areconverted back to the carboxylic acid with strong acids.

Carboxylic acids react with alcohols to produce esters.

OH

O+

O

OCH3OH + H2O

H+


Carboxylic acids react with amines to produce amides.

OH

O+

NH2

ONH3 + H2O

high temp

Amides will be discussed in more detail in sections 13.10 and 13.11.


Esters


• The simple esters are colorless, volatile liquids with a pleasant smell.

• Esters are neither acids nor bases in aqueous solution.

• An ester’s name consists of two words. The name of the alkyl group in the ester group, -COOR, and the name of the parent carboxylic acid with the family name –oic replaced with –ate; e.g. ethyl acetate: CH3(C=O)OCH2CH3

ethylacetate


Properties and Reactions of Esters


Esters

To create an ester the OH group of a carboxylic acid is replaced by an OR group. Esters cannot form hydrogen bonds with each other. Therefore, esters have lower boiling points than the carboxylic acids from which they are derived.


FORMING ESTERS FROM CARBOXYLIC ACIDS

The reactions of alcohols (R-OH) and amines(R-NH2) with carboxylic acids follow the same pattern – both replace the –OH group in the acid with another group.

Esterification: Esterification is carried out by warming a mixture of a carboxylic acid and an alcohol in the presence of a catalytic amount of a strong acid catalyst.

O O This is an elimination║ ║ reaction. Water is

R-C-OH + HO-R’ → R-C-O-R’ +H2O split outacid alcohol ester water


Aspirin and Other Over-the-Counter Carboxylic Acid Derivatives

Aspirin: A member of a group of drugs known as salicylates. Aspirin is an analgesic (relieves pain), antipyretic (reduces fever), and anti-inflammatory (reduces inflammation). Salicylates are esters of salicyclic acid.

Early people knew that chewing willow bark could relieve pain. Itwas salicylic acid in the bark that caused the effect. But the acid was bitter and caused stomach problems. In 1897 German chemists at Bayer acetylated salicylic acid and gavethe world Aspirin.


COOH

OH

+ CH3COOHCOOH

O

O CH3

H+

heat

salicylic acid aspirin

Esterification

Hydrolysis

= forward reaction (remove water)

= reverse reaction = addingwater to break a bond

acetic acid


Selected Esters That Are Used as Flavoring Agents.


Amides


Amides

• Amides may contain an –NH2 group or one or both of the hydrogens can be replaced with alkyl groups.

• Unsubstituted amides, RCONH2, can form three hydrogen bonds to other amide molecules and thus have higher melting and boiling points than the acids from which they are derived.


• Unsubstituted amides, RCONH2, are named by replacing the –oic acid by –amide.

• Substituted amides are named by first specifying the alkyl group and then identifying the amide name. The alkyl substituents are preceded by the letter N to specify that the alkyl groups are attached to the nitrogen.


Note on Naming These Compounds

H- gives “form-” CH3- gives “acet-”

HCOOH = formic acid CH3-COOH = Acetic acid

HCOO- = formate ion CH3-COO- = acetate ion

H(C=O)H = formaldehyde CH3(C=O)H = acetaldehyde

H(C=O)NH2 = formamide CH3(C=O)NH2 = acetamide

Examples: CH3(C=O)CH3 = acetone

H(C=O)N(CH3)2 = N,N-dimethylformamide

CH3(C=O)NH-CH2CH3 = N-ethylacetamideacetamide ethyl


NAIL POLISH SOLVENTS

CH3(C=O)CH3 = acetone

CH3(C=O)-O-CH2CH3 = ethylacetate

acetate ethyl

The Merck Index: “Caution: Inhalation may produceheadache, fatigue, excitement, bronchial irritation, and, in large amounts, narcosis. Serious poisoning rare.”


Chemistry at a Glance:Summary of Structural Relationships for Hydrocarbon

Derivatives: “H” versus “R”


Urea is a one-carbon amide. Its formation is the human body’s primary method of eliminating nitrogen “waste”.

The kidneys remove urea from the blood and provide a route for its excretion into the urine. When the kidneys malfunction, urea concentration builds up to toxic levels, a condition known as uremia.

H 2N N H 2

O

Note that urea is like acetone with the -CH3 groups replaced by -NH2 groups


Tylenol, a.k.a. acetaminophen, is an amide.

HN

OH

O

In this case the amine component is an aniline. TheIUPAC name is …

Tylenol

N-(4-hydroxyphenyl)-acetamide.


Properties and Reactions of Amides


Amide Formation: Amides are formed by heating a mixture of a carboxylic acid and an amine. (The reaction is best accomplished by treating an acid chloride with ammonia or an amine.)

Cl

O+ NH3 NH2

O+ HCl

Cl

O+ NH2R N

H

O+ HClR

Cl

O+ N

O+ HClRHN R

R' R'


Acetaminophen: An amide that also contains a hydroxyl group. It is best known as Tylenol. It is an alternative to aspirin for pain relief, but unlike aspirin it is not an anti-inflammatory agent.


Hydrolysis of Esters and Amides

Recall: Hydrolysis means the addition of water to split a bond.

Esters and amides undergo hydrolysis to give back the carboxylic acid and alcohol or amine.

Ester hydrolysis: Ester hydrolysis reactions can be catalyzed by either an acid or a base.

O

O+ NaOH

ONa

O+ CH3OH


• Acid catalyzed ester hydrolysis is simply the reverse of esterification reaction. In this reaction, an ester is treated with water in the presence of a strong acid catalyst such as sulfuric acid.

• Base catalyzed ester hydrolysis with a base such as NaOH or KOH is known as saponification. The product of a saponification reaction is a carboxylate anion rather then a free carboxylic acid.


Amide hydrolysis: Amides are stable in water, but undergo hydrolysis when heated in the presence of a base or an acid. The products of amide hydrolysis reactions in the presence of a base or an acid are shown below.


Errors in the Text

Question 13.25(d). The ring part of the structure shown should be a phenyl (benzene) group., i..e., a hexagon with a circle inside.

On page 353: In the “Chemical Portrait” the structure shown isactually acetaldehyde, not acetone. (The text is correct for acetone.)

Acetone is CH3-(C=O)-CH3

Bonuses: Students who are first to point out any error in the text in the chapters we cover will receive a bonus of 2 points.


Condensation Polymers: Polyesters and Polyamides


These are formed by reacting difunctional monomers to give a polymer and a small molecule, usually water or HCl. Note: condensation is the reverse of hydrolysis.

O

OH

O

HO HOOH+

O

O

O

HO OH + H2O

O

O

O

O O

O O

OO

Poly(ethylene terephthalate), a polymer = PET

A polyester polymer is a condensation polymer inwhich the monomers are joined through ester linkages.

CONDENSATION POLYMERS

diacid dialcohol


Polyamides and Polyesters

• Polymer molecules are composed of thousands of repeating units, known as monomers.

• Both polyamides and polyesters are polymers; they have many uses.

• Polyamides are formed by reaction between diamines and diacids.

• Nylons are polyamides.

• Polyesters are formed by reaction between diacids and dialcohols.


A polyamide is a condensation polymer in which the monomers are joined through amide linkages.

H2NNH2

1,6-hexanediamine

HO

O

O

OH+

hexanedioic acid

HNHN

NHO

O HN

O

O

Nylon 66


A white strand of a nylon polymer forms between two layers of a solution containing a diacid (bottom layer) and a diamine (top layer).


Polyurethanes are polymers related to polyesters andpolyamides. The backbone of a polyurethane polymercontains aspects of both ester and amide functionalgroups.

O NH

HN O

O NH

HN O

O NH

O

O

O

O

O

Foam rubber in furniture upholstery (e.g. on airplanes),packaging materials, life preservers, elastic fibers, and many other products such as skin substitute membranes(Figure 13.13) contain polyurethane polymers.

POLYURETHANES


In the News

The U.S. Environmental Protection Agency (EPA) has recentlyquestioned the safety of perfluorooctanoic acid (PFOA), acompound employed in making teflon and a variety of nonstick Items.

PFOA may be a carcinogen (a cancer-causing agent).

What is the formula of PFOA?

• “Perfluoro” means that all of the hydrogens attached to the carbons

in the compound have been replaced by fluorine atoms.• “Octanoic acid is an organic acid with 8 carbons, thus

PFOA = CF3-(CF2)6-COOH

Note that the acid hydrogen is not replaced by a fluorine.


Chapter Summary

• Carbonyl compounds contain a carbonyl group (C=O).

• Carbonyl groups are strongly polarized, with a partial positive charge on carbon and partial negative charge on oxygen.

• Carbonyl compounds are broadly divided into two groups: aldehydes and ketones are in one group and the second group contains carboxylic acids, esters, and amides.


Chapter Summary (Cont’d)

• Systematic or IUPAC names for aldehydes are derived by replacing –e at the end of the name of the alkane with –al.

• Ketones are named systematically by replacing the final –e of the corresponding alkane name with –one.

• Aldehydes and ketones do not form hydrogen bonds, as a result they have lower boiling points than alcohols of similar size.


Chapter Summary (cont’d)

• Aldehydes and ketones are soluble in common organic solvents, and those with fewer then five carbons are also soluble in water.

• Simple ketones are excellent solvents because they dissolve both polar and nonpolar compounds.

• Alcohols can be oxidized to aldehydes and ketones.• Aldehydes can be further oxidized to carboxylic acids.• Aldehydes are reduced to primary alcohols, and ketones

are reduced to secondary alcohols.


Chapter Summary (cont’d)• Most carboxylic acids are weak acids but esters

and amides are neither acids nor bases.• Carboxylic acids, esters, and amides undergo

carbonyl group substitution reactions.• Simple acids and esters are liquids; all amides

except formamide are solids.• In esters, the -OH group in the acid is replaced by

an -OR group of an alcohol.• In amides, the -OH group in an acid is

replaced by an –NH2 group of ammonia, or an NHR or –NR2 group of a primary or secondary amine.


What you absolutely must know from Chapter 13

• You must know the general forms of the following compounds:

Aldehyde Ketone Carboxylic Acid Ester Amide

• How to name aldehydes, ketones, carboxylic acids, and esters.

• The common names of certain simple compounds: formaldehyde, acetone, formic acid, benzaldehyde, urea, formamide, acetamide,

• Some important reactions:--Primary alcohols can be oxidized to form aldehydes.--Secondary alcohols can be oxidized to form ketones.--Aldehydes can be further oxidized to form carboxylic acids.--Ketones resist oxidation--Esters can be hydrolyzed to form an alcohol and a carboxylic acid--Amides can be hydrolyzed to form an amine and a carboxylic acid

(Hydrolysis = adding water to split up a compound)


Chapter 13 (continued)

• Polymers are large compound formed by linking smaller units called monomers.

• Condensation polymers are formed by reacting difunctionalmonomers and splitting out small molecules (e.g., H2O):

--A polyester is formed by the reaction of a diacid and a dialcohol:

HOOC-R-COOH + HO-R’-OH → HOOC-R-CO-O-R’-OH + H2Oester link

--A polyamide (such as nylon) can be formed from the reaction of a diacid and a diamine:

HOOC-R-COOH + HHN-R’-NH → HOOC-R-CO-NH-R’-OH + H2Oamide link


To Do List

• Read chapter 13!!

• Do additional problems

• Review Lecture notes forChapter Thirteen

• Do practice test T/F

• Do practice test MC

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Hydrogen bonds These require both positive hydrogens · PDF file-Hydrogen bonds These require both positive hydrogens ... have lower densities and lower boiling points ... Chapter