theme: structure and chemical properties of carboxylic acids. heterofunctional compounds
DESCRIPTION
LECTURE 2. THEME: Structure and chemical properties of carboxylic acids. Heterofunctional compounds. Lecturer : Yevheniya. B. Dmukhalska. Plan Nomenclature of carboxylic acids Physical properties of carboxylic acids. Classification of carboxylic acids - PowerPoint PPT PresentationTRANSCRIPT
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).