THEME: Structure and chemical THEME: Structure and chemical properties of carboxylic acids. properties of carboxylic acids. Heterofunctional compounds.Heterofunctional compounds.

LECTURELECTURE 22

LecturerLecturer: Yevheniya. B. DmukhalskaYevheniya. B. Dmukhalska

PlanPlan1. Nomenclature of carboxylic acids2. Physical properties of carboxylic acids.3. Classification of carboxylic acids4. Methods of preparation of carboxylic acids5. Chemical properties of carboxylic acids.6. Heterofunctional compounds. 7. Hydroxy-acids, nomenclature, isomerism,

chemical properties and specific reactions for hydroxy-acids.

8. Introduction of optical isomerous. Mirror (optical) isomerism. Asymmetric carbon atom. Properties of enantiomers.

Carboxylic acids Carboxylic acids Carboxylic acids Carboxylic acids are compounds whose are compounds whose characteristic functional group is the carboxyl characteristic functional group is the carboxyl group group -- COOH COOH , example: , example:

Common formula of carboxylic acid: Common formula of carboxylic acid:

Nomenclature of carboxylic acidsNomenclature of carboxylic acids

Nowhere in organic chemistry are common names used more often than with the carboxylic acids. Systematic names for carboxylic acids are derived by counting the number of carbons in the longest continuous chain that includes the carboxyl group and replacing the -e ending of the corresponding alkane by -oic acid.

Table 1. Systematic and common names of some carboxylic acids

Classification of carboxylic acids : Classification of carboxylic acids : 1. From the nature of hydrocarbon radical:1. From the nature of hydrocarbon radical:a) a) saturated acid is acid, which has only simple bonds saturated acid is acid, which has only simple bonds

in molecule. Example: formic acid, buthanic acid;in molecule. Example: formic acid, buthanic acid;b) b) unsaturated acid is an acid, which has both as unsaturated acid is an acid, which has both as

simple bonds and duble bonds in molecule. simple bonds and duble bonds in molecule. Example: oleic acid, linoleic acid, linolenic acid, Example: oleic acid, linoleic acid, linolenic acid, arashdonic acid;arashdonic acid;

c) ac) aromacic acid is acid, which contain aromatic ring. romacic acid is acid, which contain aromatic ring. Example: benzoic acid.Example: benzoic acid.

2.2. The number of carboxyl groupsThe number of carboxyl groupsa) monocarboxylic acid is acid, which has one a) monocarboxylic acid is acid, which has one

carboxylic group in molecule. Example: acetic carboxylic group in molecule. Example: acetic acid, formic acid, buthanic acid;acid, formic acid, buthanic acid;

b) dicarboxylic acid is acid, which has two carboxylic b) dicarboxylic acid is acid, which has two carboxylic group in molecule. Example: oxalic acid, malonic group in molecule. Example: oxalic acid, malonic acid.acid.

The names of some saturated monocarboxylic acids

Structural formula Name of nomenclature

trivial substitute rational

formic acid methanoic acid -

acetic acid etanoic acid acetic acid

propionic acid

propanoic acid methylacetic acid

oil acid butanoic acid ethylacetic acid

iso oil acid 2-methylpropanoic acid

dimethylacetic acid

valeric acid pentanoic acid propylacetic acid

iso valeric acid

3-methylbutanoic acid

methylethylacetic acid

CH3-(CH2)4-COOH capronic acid hexanoic acid n-butylacetic acid

CH3-(CH2)10-COOH lauric acid dodecanoic acid

CH3-(CH2)12-COOH myristic acid tetradecanoic acid

CH3-(CH2)14-COOH palmitic acid hexadecanoic acid

CH3-(CH2)16-COOH stearic acid octadecanoic acid

CO

OHCH3

CH3 CH CH2

1234

CH3 CH2C

O

OHCH2 CH2

CH3 CH CO

OH

CH3

123

CH3 CH2C

O

OHCH2

CH3 CH2C

O

OH

CH3 CO

OH

H CO

OH

The names of some unsaturated monocarboxylic acids

Structural formula Name of nomenclature

trivial substitute

CHCH22=CH-COOH=CH-COOH acrylic acid propenoic acid

methacrylic acid 2-methylpropenoic acid

CHCH22=CH-CH=CH-CH22-COOH-COOH vinyl acetic acidvinyl acetic acid 3-butenoic acid

crotonic acid trans-2-butenoic acid

iso crotonic acid cus-2-butenoic acidcus-2-butenoic acid

propiolic acid propionoic acid

tetrolic acid 2-butynoic acid

oleic acid cus-9-octadecenoic acid

Linoleic acid cus-9-cus-12-octadecadienoic acid

linolenic acid cus-9-cus-15-octadecatrienoic acid

CH

CCH2 COOH

3

C CCOOH

H

H

CH3

C CH

COOH

H

CH3

CH C COOH

C COOHCCH3

4 3 2 1

CH

CH (CH2)7 CH3

(CH2)7 COOH

CH

CH

(CH2)4CH3

CH2CH

CH (CH2)7 COOH

CH

CH3

CH2

CH2CH

CH CH2

COOH

CHCH

CH (CH2)7

The names of some dicarboxylic acids

Structural formula Name of nomenclature

trivial substituteHOOC-COOH oxalic acid ethandioic acidethandioic acid

HOOC-CH2-COOH malonic acidmalonic acid propandioic acidpropandioic acid

HOOC-CH2-CH2-COOH succinic acid butandioic acidbutandioic acid

HOOC-CH2-CH2-CH2-COOH glutaric acid pentandioic acidpentandioic acid

HOOC-CH2-CH2-CH2-CH2-COOH adypinic acid hexandioic acidhexandioic acid

HOOC-(CH2)5-COOH pimelic acid heptadioic acidheptadioic acid

HOOC-(CH2)6-COOH cork acid octandioic acidoctandioic acid

maleic acidmaleic acid cus-butendioic acidcus-butendioic acid

fumaric acid trans-butendioic acid trans-butendioic acid

phthalic acid 1,2-benzoldicarbonic acid1,2-benzoldicarbonic acid

iso iso phthalic acid 1,3-benzoldicarbonic acid1,3-benzoldicarbonic acid

C C

COOHHOOC

HH

C C

HOOC

HCOOH

H

COOH

COOH

COOH

COOH

Physical properties of carboxylic acids.Physical properties of carboxylic acids.

The melting points and boiling points of carboxylic acids are higher than those of hydrocarbons and oxygen-containing organic compounds of comparable size and shape and indicate strong intermolecular attractive forces.

The hydroxyl group of one carboxylic acid molecule acts as a proton donor toward the carbonyl oxygen of a second. In a reciprocal fashion, the hydroxyl proton of the second carboxyl function interacts with the carbonyl oxygen of the first.

Methods of preparation of carboxylic acids.Methods of preparation of carboxylic acids.

1. Oxidation of alkylbenzenes.

2. 2. Oxidation of primary alcohols. Potassium permanganate, potassium chromate and chromic acid convert primary alcohols to carboxylic acids by way of the corresponding aldehyde.

3. Oxidation of aldehydes. Aldehydes are particularly sensitive to oxidation and are converted to carboxylic acids by a number of oxidizing agents, including potassium permanganate and chromic acid.

44. Synthesis of carboxylic acids by the preparation and . Synthesis of carboxylic acids by the preparation and hydrolysis of nitriles.hydrolysis of nitriles.

Once the cyano group has been introduced, the nitrile is subjected to hydrolysis. Usually this is carried out in aqueous acid at reflux.

Chemical properties of carboxylic acids.Chemical properties of carboxylic acids.

Formation of acyl chlorides. Thionyl chloride reacts with carboxylic acids to yield acyl chlorides.

Formation of acyl chlorides. RReaction with eaction with halo-compoundshalo-compounds::

 

Reduction reaction.

Carboxylic acids are reduced to primary alcohols by the powerful reducing agent lithium aluminum hydride.

Acidity:Acidity: IontzationIontzation::

Reactions involving the ОН-bond Reactions involving the ОН-bond

Reactions involving the ОН-bondReactions involving the ОН-bond

a) Important reaction of carboxylic acids involving the ОН bond - the reaction with bases to give salts.

b) Another important reaction involving this bond is the reaction of carboxylic acids with diazomethane. The products of this reaction are the methyl ester and nitrogen.

ESTERIFICATIONESTERIFICATION This page looks at esterification - mainly the This page looks at esterification - mainly the

reaction between alcohols and carboxylic acids reaction between alcohols and carboxylic acids to make esters.to make esters.

αα-halogenation of carboxylic acids-halogenation of carboxylic acidsThe enol content of a carboxylic acid is far less than that of an aldehyde or

ketone, and introduction of a halogen substituent at the -carbon atom requires a different set of reaction conditions. Bromination is the reaction that is normally carried out, and the usual procedure involves treatment of the carboxylic acid with bromine in the presence of a small amount of phosphorus trichloride as a catalyst.

This method of α bromination of carboxylic acids is called the

Hell–Volhard– Zelinsky reaction.

Decarboxylation of carboxylic acids. The loss of a molecule of carbon dioxide from a carboxylic acid is

known as decarboxylation.

The formation amides.The formation amides. The most common reaction of this type is the reaction of carboxylic acids with ammonia or amines to give amides. When ammonia is bubbled through butyric acid at 1850, butyramide is obtained in 85% yield. The reaction involves two stages. At room temperature, or even below, butyric acid reacts with the weak base ammonia to give the salt ammonium butyrate. This salt is perfectly stable at normal temperatures. However, pyrolysis of the salt results in the elimination of water and formation of the amide.

H2C

H2C

C

C

OH

OH

O

O

+ NH3

t

O

O

N H + H2O

succinic acidsukcynimide

Reaction formation Reaction formation carboxylic acid carboxylic acid anhydrides.anhydrides.

Acid anhydrides are the most reactive carboxylic acid derivatives.

C6H5COOH

benzoic acid

NaOHC6H5COONa + H2O

C2H5OH; H+C6H5 C

O

OC2H5

ethylbenzoath

PCl5C6H5 C

O

Clbenzoilchloride

(CH3CO)2O; H+

C6H5 C

O

OC

O

C6H5

+

+ +

+

H2O

HCl POCl3

CH3COOH2

anhydride of benzoic acid

HOOC CH2 CH2 COOH

succinic acidHOOC CH CH COOH

Br Br-dibromsuccinic acid

HOOC CH CH2 COOHchlorsuccinic acid

H2

Br2

HCl

COOH

CH

CH

COOHbutendioic acid

HOH; H+

[O]

KMnO4

HOOC CH CH2 COOH

malic acid

HOOC CH CH COOH

racemic acid

2, 3

8. Carboxylic acid derivatives.8. Carboxylic acid derivatives.

These classes of compounds are classified as carboxylic acid derivatives. All may be converted to carboxylic acids by hydrolysis.

Functional Group is any part of an organic compound, which is not а carbon-hydrogen or carbon-carbon single bon.There are mono-, poly- and heterofunctional group in the structure of organic compounds:

Monofunctional group – contains only 1 functional group.

C2H5—OH

Polyfunctional group – contains several similar functional group.H2C

CH

H2C

OH

OH

OH

Heterofunctional group – contains several different functional group.

Sphingosine

Biological role:Biological role: Heterofunctional compounds are widespread in the Heterofunctional compounds are widespread in the

nature. They are in fruits and vegetable leafs. Also nature. They are in fruits and vegetable leafs. Also they are formed in body. So, the lactic acid is they are formed in body. So, the lactic acid is product of transformation glucose (glycolysis) in product of transformation glucose (glycolysis) in human body. A malic and citric acid formed in a human body. A malic and citric acid formed in a cycle of tricarboxylic acids, which is also known as cycle of tricarboxylic acids, which is also known as citric acid cycle or Krebs' cycle. Hydroxo acids citric acid cycle or Krebs' cycle. Hydroxo acids such as: pyruvic acid, acetoacetic acid, oxaloacetic such as: pyruvic acid, acetoacetic acid, oxaloacetic acid, acid, -ketoglutaric acid are important in -ketoglutaric acid are important in metabolism of carbohydrates.metabolism of carbohydrates.

HydroxyacidsHydroxyacids HydroxyacidsHydroxyacids are the derivatives of carboxyl acids that are the derivatives of carboxyl acids that

contain –OH group (1 or more).contain –OH group (1 or more).

3 2 1CH3C CH

O

OHOH

β α

2-hydroxypropanoic acidα-hydroxypropanoic acid

tartaric acidα,α’-dihydroxysuccinic acid,2,3-dihydroxybutandioic acid,

lactic acid,α- hydroxypropanoic acid,2- hydroxypropanoic acid

malic acid,hydroxysuccinic acidhydroxybutanedioic acid

citric acid,2-hydroxy-1,2,3-propantricarboxylic acid

glycolic acid,hydroxyacetic acid,hydroxyethanoic acid

In a row of hydroxyacids often found the optical In a row of hydroxyacids often found the optical isomery.isomery.

D-tartaric acid

L-tartaric acid

mezo-tartaric acid

Methods of preparation of hydroxyacids:1.1. Hydrolysis of α-halogenoacidsHydrolysis of α-halogenoacids

2.2. Oxidations of diols and hydroxyaldehydesOxidations of diols and hydroxyaldehydes

3.3. Hydration of α,β-unsaturated carboxylic acidsHydration of α,β-unsaturated carboxylic acids

CH3C CH

O

OHCl

NaOHH2O CH3C CH

O

OHOH

NaCl+ +

lactic acidlactic acid

CH3C CH

O

HOH

CH2H3C CH

OHOH

CH3C CH

O

OHOH

[O] [O]

CH CO

OHH2O+CH2 CH2C CH2

O

OH

H+

OH

ββ-hydroxypropanoic acid-hydroxypropanoic acid

4. Hydrolysis of hydroxynitriles (cyanohydrins)4. Hydrolysis of hydroxynitriles (cyanohydrins)

Physical and chemical properties of

hydroxycarboxylic acid For For physical propertiesphysical properties of hydroxycarboxylic acids are of hydroxycarboxylic acids are

colorless liquids or crystalline substance, soluble in water.colorless liquids or crystalline substance, soluble in water.

Chemical properties:Chemical properties: in the molecule of hydroxyacids ether – in the molecule of hydroxyacids ether –OH group or carboxyl group can react.OH group or carboxyl group can react.

Carboxyl group can react forming:Carboxyl group can react forming:

a) salts:a) salts:

H2C CH2 CO

OHOH

NaOH H2C CH2 CO

ONaOH

H2O+ +

sodium sodium ββ-hydroxypropanoic acid-hydroxypropanoic acid

2 H2C CH2 CO

OHOH

2 Na 2 H2C CH2 CO

ONaOH

H2+ +

b) Ester formation:b) Ester formation:

2 H2C CH2 CO

OHOH

MgO

H2C CH2 CO

OMg

O

CO

H2C CH2

OH

OH

H2O+ +

H2C CH2 CO

OHOH

NaHCO3 H2C CH2 CO

ONaOH

H2CO3

H2O CO2

++

H2C CH2 CO

OH++

OH

H2OHO CH3 H2C CH2 CO

OOH

CH3

Methyl-Methyl-ββ-hydroxypropanoate-hydroxypropanoate

c) Amides formation:c) Amides formation:

II. –OH group reaction:II. –OH group reaction:

a)a) hydrohalogens (HCl, HBr, HI, HF)hydrohalogens (HCl, HBr, HI, HF)

b) can oxidizeb) can oxidize

H2C CH2 CO

OH+NH3+

OH

H2C CH2 CO

NH2OH

H2Ot=200o

amide of amide of ββ-hydroxypropanoic acid-hydroxypropanoic acid

HCl ++ H2OH2C CH2 CO

OHCl

CH2C CH2

O

OHOH

+ H2OCH2C CH2

O

OH

[O]

OH

CHC CH2

O

OHO

ββ-oxopropanoic acid-oxopropanoic acid

lactic acid lactide

Related to heat of:

1. α-hydroxyacids

2. β-hydroxyacids

3. γ-hydroxyacids

H

O

C

O H

C H 3

O

C

H

+

O

O H

CС H 3 С

O H

H

H 2S O 4к .

t

HCOOH CO + H2Oк. Н2SO4, t

Ñ ÑH2COOHHOOCH2C

OH

COOH

H CO

OHC CH2COOH

O

HOOCH2C

C CH3CH3

O

ê. H2SO4 +

CO H2O 2 CO2

t acetidicarbonic acid

Decomposition α-hydroxyacids

Ethanal formic acid

Representatives of hydroxyacids:Representatives of hydroxyacids: lactic acidlactic acid. lactic acid is a trivial name . lactic acid is a trivial name

because at first it was extracted because at first it was extracted from milk. It from milk. It is present in yogurt, sour milk is present in yogurt, sour milk and other milk products. It can form in muscles during hard and other milk products. It can form in muscles during hard and prolonged work. Salts of milk acid are used in medicine.and prolonged work. Salts of milk acid are used in medicine.

Malic acidMalic acid. It is present in green apples . It is present in green apples andand

some berries. It takes part in biological some berries. It takes part in biological processes in human organisms processes in human organisms

and organisms of other alive creatures. It is used in and organisms of other alive creatures. It is used in medicine for synthesis of some medical preparations.medicine for synthesis of some medical preparations.

Tartaric acidTartaric acid . It is present in grape. It . It is present in grape. It is is used in medicine for synthesis of some used in medicine for synthesis of some

medical preparations.medical preparations.

CH3C CH

O

OHOH

CH2 CO

OHCHC

O

HOOH

CH

CH

C

C

OH

OH

O

OH

O

OH

Citric acidCitric acid . It . It is present in is present in orange, lemon and other orange, lemon and other

citric fruits. It takes citric fruits. It takes part in part in biological biological processes in processes in human human organism.organism.

HO C

CH2

C

CH2OH

O

C

C

O

OH

O

OH

Phenolacids.Phenolacids.

o-hydroxycinnamic acid salicylic acid,2-hydroxybenzoic acid

4-hydroxybenzoic acid

3,4,5-trihydroxybenzoic acid,gallic acid

PhenolacidsPhenolacids are the derivatives of aromatic carboxyl acids that are the derivatives of aromatic carboxyl acids that contain –OH group (1 or more).contain –OH group (1 or more).

COOH

OH OH

COONa+ CO2+ NaHCO3 + H2O

salicylic acid

Chemical properties of phenolacids: Chemical properties of phenolacids: Chemical properties ofChemical properties of phenolacids due to the phenolacids due to the

presence in their structure of carboxyl group, phenolic hydroxyl presence in their structure of carboxyl group, phenolic hydroxyl and the aromatic nucleus.and the aromatic nucleus.

DecarboxylationDecarboxylation

The best known aryl ester is O-acetylsalicylic acid, better The best known aryl ester is O-acetylsalicylic acid, better known as aspirin. It is prepared by acetylation of the phenolic known as aspirin. It is prepared by acetylation of the phenolic hydroxyl group of salicylic acid:hydroxyl group of salicylic acid:

Aspirin possesses a number of properties that make it an Aspirin possesses a number of properties that make it an often-recommended drug. It is an analgesic, effective in often-recommended drug. It is an analgesic, effective in relieving headache pain. It is also an antiinflammatory agent, relieving headache pain. It is also an antiinflammatory agent, providing some relief from the swelling associated with arthritis providing some relief from the swelling associated with arthritis and minor injuries. Aspirin is an antipyretic compound; that is, and minor injuries. Aspirin is an antipyretic compound; that is, it reduces fever. Each year, more than 40 million lb of aspirin it reduces fever. Each year, more than 40 million lb of aspirin is produced in the United States, a rate equal to 300 tablets is produced in the United States, a rate equal to 300 tablets per year for every man, woman, and child.per year for every man, woman, and child.

OxoacidsOxoacidsTo oxoacids include aldehydo- and ketonoacids. To oxoacids include aldehydo- and ketonoacids. These compounds include in the structure of the These compounds include in the structure of the carboxyl group, aldehyde functional group or ketone carboxyl group, aldehyde functional group or ketone functional group.functional group.

γ-ketovaleric acid,4-oxopentanoic acid,levulinic acid

acetoacetic acid,3-oxobutanoic acid,β-ketobutyric acid

oxalacetic acid,oxobutanedioic acid,ketosuccinic acid

glyoxylic acid,oxoethanoic acid

pyroracemic acid,2-oxopropanoic acid

Chemical properties of oxoacidsChemical properties of oxoacids1.1. Decarboxylation of Decarboxylation of αα-oxoacids-oxoacids

2.2. Decarboxylation of Decarboxylation of ββ-oxoacids-oxoacids

CH3 C

O

COOHconc. H2SO4, t

CH3 C + CO2

O

Hpyroracemic acid acetaldehyd

CH3 C

O

t

acetoacetic acid

CH2 COOH CH3 C CH3

Oacetone

- CO2

StereochemistryStereochemistry The three-dimensional shape of an organic The three-dimensional shape of an organic

molecule can have а dramatic effect upon molecule can have а dramatic effect upon its reactivity. In fact, the study of the its reactivity. In fact, the study of the shapes of organic molecules is so shapes of organic molecules is so important that it forms а separate sub-important that it forms а separate sub-discipline within organic chemistry — discipline within organic chemistry — stereochemistry, from the Greek word stereochemistry, from the Greek word ““” (stereos), meaning solid; this ” (stereos), meaning solid; this chapter will be devoted to the study of chapter will be devoted to the study of organic molecules in three dimensions. organic molecules in three dimensions.

Compounds which differ in the three-Compounds which differ in the three-dimensional arrangement of the atoms in dimensional arrangement of the atoms in space but have the same connectivity are space but have the same connectivity are termed stereoisomers.termed stereoisomers.

StereoisomersStereoisomers are compounds that have are compounds that have the same sequence of covalent bonds and the same sequence of covalent bonds and differ in the relative disposition of their differ in the relative disposition of their atoms in space. atoms in space.

StereoisomersStereoisomers

There are two major causes of There are two major causes of stereoisomerism: stereoisomerism:

1.1. the presence of "structural rigidity" in а the presence of "structural rigidity" in а molecule. Structural rigidity is caused molecule. Structural rigidity is caused by restricted rotation about chemical by restricted rotation about chemical bonds. It is the basis for cis - trans bonds. It is the basis for cis - trans stereoisomerism, а phenomenon stereoisomerism, а phenomenon found in some substituted found in some substituted cycloalkanes and some alkenes;cycloalkanes and some alkenes;

2.2. the presence of а chiral center in а the presence of а chiral center in а molecule.molecule.

COFORMATIONCOFORMATION

The methyl groups can rotate freely about The methyl groups can rotate freely about the central C–C bond. Structures that the central C–C bond. Structures that differ only by rotation about one or more differ only by rotation about one or more single bonds are defined as single bonds are defined as conformations of a compound.conformations of a compound.

For example: Ethane has two For example: Ethane has two conformations: eclipsed structure, which conformations: eclipsed structure, which is more higher in energy than the more is more higher in energy than the more stable staggered structure. stable staggered structure.

The stereoisomers that are not easily The stereoisomers that are not easily interconverted are called interconverted are called configurational isomers.configurational isomers.

ConfigurationConfiguration

The concept of mirror images is the key to The concept of mirror images is the key to understanding molecular handedness. All understanding molecular handedness. All objects, including all molecules, have mirror objects, including all molecules, have mirror images. The images. The mirror imagemirror image of an object is the of an object is the object’ reflection in а mirror. For example: object’ reflection in а mirror. For example: human hands.human hands.

Mirror ImagesMirror Images

ChiralityChirality The general property of "handedness" is The general property of "handedness" is

called called chiralitychirality. An object that is not . An object that is not superimposable upon its mirror image is superimposable upon its mirror image is chiralchiral. If an object and its mirror image . If an object and its mirror image can be made to coincide in space, then can be made to coincide in space, then they are said to be they are said to be achiralachiral. .

A person’s left and right hands are not A person’s left and right hands are not superinposable upon each other.superinposable upon each other.

Any organic molecule containing а single Any organic molecule containing а single carbon atom with four different groups carbon atom with four different groups attached to it exhibits chirality. attached to it exhibits chirality.

А А chiral centerchiral center is an atom in а molecule that is an atom in а molecule that has four different groups tetrahedrally bonded has four different groups tetrahedrally bonded to it.to it. It is It is asymmetric asymmetric atom. atom.

Enantiomers Enantiomers are stereoisomers whose are stereoisomers whose molecules are nonsuperimposable mirror molecules are nonsuperimposable mirror images of each other. images of each other.

Properties of Properties of enantiomersenantiomers

Enantiomers are said to be optically active Enantiomers are said to be optically active because of the way they interact with because of the way they interact with plane-polarized light. An optically active plane-polarized light. An optically active compound is а compound that rotates the compound is а compound that rotates the plane of polarized light.plane of polarized light.

Ordinary light waves - that is, Ordinary light waves - that is,

unpolarized light waves - vibrate in all unpolarized light waves - vibrate in all planes at right angles to their direction planes at right angles to their direction of travel. Plane-polarized light waves, of travel. Plane-polarized light waves, by contrast, vibrate in only one plane at by contrast, vibrate in only one plane at right angles to their direction of travel. right angles to their direction of travel.

PolarimeterPolarimeter

An enantiomer that rotates plane-polarized light to the An enantiomer that rotates plane-polarized light to the right is said to be dextrorotatory (the Latin dexter means right is said to be dextrorotatory (the Latin dexter means "right"). An enantiomer that rotates plane-polarized light "right"). An enantiomer that rotates plane-polarized light to the left is said to be levorotatory (the Latin laevus to the left is said to be levorotatory (the Latin laevus means "left"). means "left").

А plus or minus sign inside parentheses is used to А plus or minus sign inside parentheses is used to denote the direction of rotation of plane-polarized light by denote the direction of rotation of plane-polarized light by а chiral compound. The notation (+) means rotation to а chiral compound. The notation (+) means rotation to the right (clockwise), and (-) means rotation to the left the right (clockwise), and (-) means rotation to the left (counterclockwise). Thus the dextrorotstory enantiomer (counterclockwise). Thus the dextrorotstory enantiomer of glucose is (+)-glucose.of glucose is (+)-glucose.

An equimolar mixture of two An equimolar mixture of two enantiomers is called а enantiomers is called а racemic racemic mixturemixture, or а , or а racemate.racemate. Since а Since а racemic mixture contains equal racemic mixture contains equal numbers of dextrorotating and numbers of dextrorotating and levorotating molecules, the net optical levorotating molecules, the net optical rotation is zero. А racemic mixture is rotation is zero. А racemic mixture is often specified by prefixing the name of often specified by prefixing the name of the compound with the symbol (the compound with the symbol ( ); );

DiastereomersDiastereomers

Diastereomers Diastereomers - stereoisomers that are not - stereoisomers that are not mirror images of each other. mirror images of each other.

Epimers Epimers are diastereomers that differ only in are diastereomers that differ only in the configuration at one chiral center.the configuration at one chiral center.

In general, а compound that has n chiral centers In general, а compound that has n chiral centers may exist in а maximum of 2may exist in а maximum of 2nn stereoisomeric stereoisomeric forms. For example, when three chiral centers forms. For example, when three chiral centers are present, at most eight stereoisomers (2are present, at most eight stereoisomers (233 = 8) = 8) are possible (four pairs of enantiomers).are possible (four pairs of enantiomers).