Functional Groups in Organic
Classes of organic compounds can be distinguished
according to functional groups they contain.
A functional group is a group of atoms that is largely
responsible for the chemical behavior of the parent
It is atom or a group of atoms within a molecule that are
responsible for the characteristic reactions of a molecule.
The chemistry of every organic molecule, regardless of size
and complexity, is determined by the functional groups it
2.1. Functional Groups
• The concept of functional group is important organic chemistry for
• Functinal group serves as basic for nomenclature(naming organic
• Functional group serve to classify organic compound in to classes
(families). All families with the same functional group belong to
the same class.
• A functional group is the site of chemical reactivity in a molecule
compound in the same class have similar chemical property.
• NB A molecule can contain more than one functional group it is
said to be poly-functional
2.2.1 Akanes (Paraffine)
Alkanes are hydrocarbons in which all the bonds are single bonds
Alkanes have no functional groups
Alkanes are called saturated hydrocarbons
Open chain alkanes: - general formula, CnH2n+2 where n= 1, 2, 3,……
Cyclic alkanes (cycloalkanes):- general formula, CnH2n where n= 3,4,5,…
The formulas and structures of each successive compound differ from each
other by one methylene group (CH2) is called homologous series.
The names of alkanes are derived from the Greek prefixes that indicate the
number of carbon atoms in the molecule, and ending with “ - ane ” .
CH4 = methane, CH3-CH3 = ethane, CH3-CH2-CH3 = propane,
CH3-CH2-CH2-CH3 = butane
Naming of alkyl groups
Alkyl groups (R) are formed by removing one hydrogen atom from an
alkane. They are named by dropping –ane from the name of the
corresponding alkane, and adding the ending –yl.
Naming of non-alkyl groups
A number of non-alkyl groups are used in naming organic compounds,
some of their names are given below:
—Cl = Chloro —I = Iodo —NO2 = Nitro —OH = Hydroxy
—Br = Bromo —F = Fluoro —NH2 = Amino —NO = Nitroso
Naming system of alkanes
In general, organic compounds are given systematic names by using the
Prefix indicates how many branching groups are present.
Parent indicates how many carbons are in the longest chain.
Suffix indicates the name of the family.
The IUPAC rules for naming of alkanes are given below:
1. Select the longest continuous chain of carbon atoms; this chain determines
the parent name for the alkane.
2. Number the longest chain beginning with the end of the chain nearer the
3. Use the numbers obtained by application of rule 2 to designate the location
of the substituent group.
4. When two or more substituents are present, give each substituent a number
corresponding to its location on the longest chain and list them alphabetically
5. When two or more substituents are identical, indicate this by the use of the
prefixes di-,tri-,and so on.
6. When branching first occurs at an equal distance from either end of the
longest chain, choose the name that gives the lower number at the first point of
Properties of Alkanes
The first four alkanes are gases. While pentane and higher alkanes (
heptadecane or C17H36 ) are liquids.
Alkanes are insoluble in water but soluble in non-polar solvents. Why?
Boiling point and melting point of alkanes show regular increases as
molecular weight increases. E.g pentane has higher boiling point than
Alkanes react with oxygen with oxygen to produce CO2 and H2O and
release large amount of energy.
Alkanes undergo a sequential substitution of the alkane hydrogen atoms by
Cycloalkanes are alkanes that contain a ring of three or more carbons.
They have the general formula CnH2n , n = 3, 4, 5…..
Cycloalkanes are named under the IUPAC system by adding the prefix
cyclo to the name of the un branched alkane with the same number of
carbons as the ring.
The smallest possible ring consists of cyclo propane, C3H6.
Note that in the condensed structural formulas, there is a carbon atom at
each corner and enough hydrogen are assumed to be attached to give a total
of four single bonds.
2.2.2 Alkenes (Olefins)
Alkenes are hydrocarbons that contain a carbon-carbon double bond
(C=C) in their molecule.
Alkenes have carbon-carbon double bond (C=C) functional groups
Alkenes are called unsaturated hydrocarbons
- Acyclic alkenes: - general formula, CnH2n where n= 2, 3,……
e.g. CH3 CH2CH=CHCH3 = C5H10
- Cyclic alkenes ( cycloalkenes ):- general formula, CnH2n-2 where n= 3,4,5,..
Naming system of alkenes
1. Select the parent name by selecting the longest chain that contains the
double bond and change the ending of the name of the alkane of identical
length from -ane to -ene.
2. Number the parent chain in the direction that gives the double bond
carbons get lower numbers.
3. Indicate the locations of the substituent groups. Carbon–carbon double
bonds take precedence over alkyl groups and halogens.
4. Hydroxyl groups are outranking the double bond. Compounds that contain
both a double bond and a hydroxyl group use the combined suffix -en + -ol to
signify that both functional groups are present.
5. When there are two or three double bonds in a molecule, the ending –ane of
the corresponding alkane is replaced by –adiene or –atriene to get the name of
H2C C CH2
H2C CH CH CH2
Physical properties of alkenes
The first three alkenes (ethane, propene and butene) are gases at
C5- C14 members of alkenes are liquids.
More than C18 are solids.
All alkenes are colorless and odorless, except ethene which has a
rather pleasant odor.
Alkenes are only slightly soluble in water but dissolve freely in
In general the boiling points and melting points of alkenes increases
as the molecular weight increases.
Chemical properties of alkenes
The most important reactions of alkenes are the addition reactions.
1. Addition of Hydrogen (Hydrogenation of alkene)
Alkenes add hydrogen under pressure and in the presence of Ni, Pt, or Pd
catalyst to produce saturated hydrocarbons.
A hydrogenation reaction carried in this manner is called Catalytical
2. Addition of Halogen
Halogens (Cl2 or Br2) react with alkenes in the presence of an inert solvent
to form dihalogen derivatives.
This provides a useful test for unsaturation, the red (brown) color of the
bromine being rapidly discharge as the colorless dibromo compound is
3. Addition of Halogen Acids
Alkenes react with halogen acids (HCl, HBr or HI) to form alkyl halides.
Addition of HX to unsymmetrical alkenes follows Markovnikov’s rule.
This rule states that when an unsymmetrical reagent (HBr) add to an
unsymmetrical alkene, the positive part of the reagent (H) become attached
to the double bonded carbon which has the most hydrogen atoms.
4. Oxidation with cold KMnO4 solution
An alkene can be oxidized to a 1,2-diol either by potassium permanganate
(KMnO4) in a cold basic solution.
Since the bright purple color of KMnO4 disappears during the reaction; it is
used as a test for presence of a double bond (Baeyer’s test).
5. Oxidation with Ozone
Ozone reacts with the C=C bond is cleaved and an oxygen atom becomes
doubly bonded to each of the original alkene carbons.
Alkynes are unsaturated hydrocarbons that contain carbon - carbon
Alkynes have carbon-carbon triple bond (C≡C) functional groups
Alkynes are called unsaturated hydrocarbons
They have the general formula CnH2n-2 where n= 2,3,4,5,……
The simplest alkyne is C2H2 and is commonly known as acetylene.
Nomenclature of Alkynes
The IUPAC names of alkynes are obtained by dropping the ending –ane of
the parent alkane and adding the suffix –yne.
Select the longest chain which contain C≡C bond as a parent chain.
Number the chain from the end closer to the C≡C bond.
Indicate the position of the C≡C bond by the number of the first carbon
atom involved in the triple bond.
Physical properties of Alkynes
The first three members are gases, next eight are liquids and the higher
alkynes are solids.
They all are colorless and odorless except acetylene which has a garlic
Their boiling points and melting points show a regular increase with the
increase in molecular weights.
Alkynes generally have slightly higher boiling points than the
They are only slightly soluble in water but dissolve readily in organic
solvent such as benzene, acetone, and ethyl alcohol.
Chemical properties of Alkynes
1. Addition of Hydrogen (Reduction)
In the presence of Ni, Pt , or Pd alkynes add up two molecules of hydrogen
first forming the corresponding alkenes and finally alkanes.
The reduction can be stopped at the alkene stage by using Pd poisoned with
BaSO4 + quinoline ( Lindlar’s catalyst).
2. Addition of Halogens
Halogens add to alkynes in two steps forming a dihalide and then a
3. Addition of Halogen Acids
Hydrogen halides add to alkynes to form alkenyl halides. The
regioselectivity of addition follows Markovnikov’s rule.
A proton adds to the carbon that has the greater number of hydrogens, and
halide adds to the carbon with the fewer hydrogens.
In the presence of excess hydrogen halide, geminal dihalides are formed by
sequential addition of two molecules of hydrogen halide to the carbon–
carbon triple bond.
Alkynes are burnt in air to form CO2, H2O and heat energy.
2CH≡CH + 5O2 → 4CO2 + 2 H2O + heat energy
Aromatic hydrocarbons (Benzene and
Characteristics of aromatic compounds
1. A delocalized conjugated π system, most commonly an
arrangement of alternating single and double bonds :
2. planar structure
3. Contributing atoms arranged in one or more rings (Cyclic)
4. A number of π delocalized electrons that is, 4n + 2 number of π
electrons, where n=0, 1, 2, 3, and so on. This is known as
Nomenclature of Aromatic Compounds
1. Monosubstituted Benzenes
a. IUPAC name
t-Butylbenzene Ethylbenzene Nitrobenzene Chlorobenzene
OH C O
Toluene Styrene Phenol Benzaldehyde Benzoic acid
b. Common name
2. Disubstituted Benzenes
All disubstituted benzenes, can give rise to three possible isomers. The
differentiate between the isomers, the relative positions of the substituents
are designated by number or, more commonly, by the prefixes ortho (o: 1,2),
meta (m:1,3) or para (p:1,4).
1,2-Dibromobenzene 1,3-Dibromobenzene 1,4-Dibromobenzene
o-Dibromobenzene m-Dibromobenzene p-Dibromobenzene
When the substituents are different, they are listed in alphabetical order
1-Chloro-2-ethylbenzene 1-Bromo-3-nitrobenzene 1-Fluoro-4-iodobenzene
o-Chloroethylbenzene m-Bromonitrobenzene p-Fluoroiodobenzene
If one of the substituents is part of a parent compound, then the di
substituted benzene is named as a derivative of the parent
2-Chlorophenol 4-Nitrotoluene 3-Bromobenzoic acid
o-Chlorophenol p-Nitrotoluene m-Bromobenzoic acid
Certain disubstituted benzenes are referred to by their
Reactions of Benzene
• Even though benzene is highly unsaturated, it does not
• undergo any of the regular reactions of alkenes
Specific Electrophilic Aromatic :
X2 , FeX3
+ HX (X=Cl, Br)
RCl, AlCl 3
HONO2 , H2SO4
SO3 , H2SO4
Side-Chain Reactions of Aromatic
a. Halogenation of an Alkyl Side Chain
b. Oxidation of an Alkyl Side Chain
+ + O
Alcohols are compounds whose molecules have a hydroxyl group (-OH)
attached to a saturated carbon atom.
General formula: R-OH
Compounds in which a hydroxyl group is attached to an unsaturated carbon
atom of a double bond (i.e., C=C–OH) are called enols.
Compounds that have a hydroxyl group attached directly to a benzene ring are
Alcohols are classified as primary (10), secondary (20), and tertiary (30)
depending upon weather the –OH group is attached to a primary, a secondary, or
a tertiary carbon.
Nomenclature of Alcohols (IUPAC System)
Parent Hydrocarbon is the longest continuous chain that contains the –OH
Change the name of the alkane corresponding to this chain by dropping the
ending –e and adding the suffix –ol.
Number the chain in direction that gives functional group the lowest
If both a substituent and a functional group are present, the functional
group gets the lower number
If the functional group gets the same number when counted from both
directions, use direction which gives the substituent the lower number
If there is more than one substituent, cite substituents in alphabetical order
Physical properties of alcohols
Lower alcohols are colourless, toxic liquids. They have a characteristics
Boiling points of alcohols increase regularly with the increase in the
number of carbon atoms.
Boiling points of alcohols are much higher than those of the corresponding
Lower alcohols (C1 to C3) are completely soluble in water. As we go
higher in the series, the water solubility falls rapidly.
Chemical reactions of alcohols
1. Reaction with Active Metals
Alcohols react with sodium or potassium to form alkoxides with the
liberation of hydrogen gas.
2. Reaction with Hydrogen Halides
Alcohols react with hydrogen halides (HX) to form the corresponding alkyl
3. Dehydration of Alcohols to Alkenes
Alcohols undergo dehydration reaction when they are treated with
concentrated H2SO4 to an alkene.
Dehydration of secondary and teriary alcohols containing four or more
carbon atoms give a mixture of two alkenes.
The alkene produced in greater abundance is indicated by Zaitsev’s rule.
It states that the alkene formed preferentially is the one containing the
higher number of alkyl groups.
4. Dehydration of Alcohols to Ethers
Primary alcohols are converted to ethers on heating in the presence of an
acid catalyst, usually sulfuric acid.
This kind of reaction is called a condensation.
A condensation is a reaction in which two molecules combine to form a
larger one while liberating a small molecule.
5. Reaction with Carboxylic Acid
Alcohols react with carboxylic acids to form esters, concentrated H2SO4 is
used as a catalyst.
This reaction is called Esterification.
6. Oxidation of Alcohols
Alcohols can undergo oxidation reaction and the nature of the product
depends on the type of alcohol and the conditions of the reaction.
Most widely used oxidizing agents are KMnO4 + H2SO4 or Na2CrO7 +
Oxidation of alcohols can be used to distinguish between primary,
secondary, and tertiary alcohols.
Primary alcohols are first oxidized to aldehydes then to carboxylic acids.
Secondary alcohols are oxidized to the corresponding ketones.
Tertiary alcohols are stable to oxidation under normal conditions.
• Ethers are a class of compounds which contain an
oxygen atom bonded to two alkyl groups. They are
further designated as symmetrical ethers or un
symmertrical ethers according as the two alkyl
groups attached to the oxygen are same or
Nomenclature of Ethers
• The two alkyl groups attached to oxygen are named in
alphabetic order and the word ether is added.
• If the two alkyl groups are same, the prefix di- is used.
Ethyl methyl ether Dimethyl ether
• In this system, ethers are named Alkoxyalkanes.
• The larger of the alkyl groups is considered to be the
• The name of the alkane is prefixed by the name of the
alkoxy group and position number.
•Names of some common alkoxy groups (RO-) are given below:
CH3O- methoxy CH3CH2O- ethoxy CH3CH2CH2O- propoxy
Physical properties of ethers
Dimethyl ether and ethyl methyl ether are gases. All other are
colorless liquids with pleasant odors.
Lower ethers are highly volatile and very flammable.
Boiling points of ethers show a gradual increase with the increase in
Ethers are slightly soluble in water. This is because they can form
hydrogen bonds with water.
Ethers have lower boiling points than isomeric alcohols ? Why?
This is because ether molecules cannot form hydrogen bonds with
each other as they have no –OH groups.
Chemical Reactions of Ethers
Ethers are unreactive to many reagents used in organic chemistry, a
property that accounts for their wide use as reaction solvents.
Halogens, dilute acids, bases, and nucleophiles have no effect on
In fact, ethers undergoonly one truly general reaction—they are
cleaved by strong acids. Aqueous HBr and HI both work well, but HCl
does not cleave ethers.
• Amines are organic derivatives of ammonia in which
one or more of the hydrogens of ammonia have been
replaced by alkyl groups.
Classification of Amines
• Amines are classified as
• The classification depends on how many alkyl groups
are bonded to the nitrogen.
• Primary amines have one alkyl group bonded to the
nitrogen, secondary amines have two, and tertiary
amines have three.
Amines are further divided into aliphatic, aromatic, and
Aliphatic amine: An amine in which nitrogen is bonded
only to alkyl groups.
• Aromatic amine: An amine in which nitrogen is bonded to
one or more aryl groups.
Heterocyclic amine: An amine in which nitrogen is one
of the atoms of a ring.
(heterocyclic aliphatic amines) (heterocyclic aromatic amines)
Nomenclature of Amines
• Amines are named as “ alkylamines ”
• The entire name is written as one word.
• Amines bearing two or three similar alkyl groups are indicated
by the prefix di- or tri-
• Amines bearing dissimilar alkyl groups are named as the N-
substituted derivative of the larger alkyl group.
• Aromatic amines are called Anilines
• IUPAC name
• Amines are named just as we do alcohols, i.e. by dropping the final
-e ending from the alkane name and adding the suffix -amine.
• Amines have a lower priority than do alcohols, which in turn are
lower than carbonyls when the amine is a substituent; it is termed
an amino group.
• Physical properties amines
– Low molecular-weight amines tend to have sharp,
penetrating odors similar to ammonia. Higher
molecular-weight amines often smell like rotting fish,
and are often found in decaying animal tissues.
– Primary amines (RNH2) & secondary amines (R2NH)
possess N-H bonds & can thus form hydrogen bonds
to each other, accounting for their higher boiling
• Tertiary amines (R3N) have no N-H bonds, cannot form hydrogen
bonds to each other, & thus, have lower boiling points than the
other two classes of amines.
Amines that have fewer than six or seven carbon atoms are soluble
in water. Primary and secondary amines are more soluble than
tertiary because they have more H-bonding with water
Chemical Reactions of Amines
1. Reaction of Amines with Alkyl Halides
Alkylations of primary and secondary amines are difficult to control
and often give mixtures of products, but tertiary amines are cleanly
alkylated to give quaternary ammonium salts.
Reactions of Primary Amines with Aldehydes and Ketones
Imines are formed by nucleophilic addition of a primary amine to the carbonyl group
of an aldehyde or a ketone.
•Reactions of Secondary Amines with Aldehydes and Ketones
Enamines are formed in the corresponding reaction of secondary
amines with aldehydes and ketones.
•Reaction of Amines with Nitrous Acid
Nitrous acid (HNO2 or HONO) reacts with aliphatic amines in a
fashion that provides a useful test for distinguishing primary,
secondary and tertiary amines.
-Amine +HONO(coldacidicsolution) AnInsolubleOil(N-Nitrosoamine)
-Amine +HONO(coldacidicsolution) AClearSolution(AmmoniumSaltFormation)
Aldehydes and Ketones
• The carbonyl group (C=O) is found in aldehydes, ketones, and
many other organic functional groups.
• Aldehydes and ketones are simple compounds which contain a
carbonyl group - a carbon-oxygen double bond.
• In ketones, two carbon groups are attached to the carbonyl carbon,
• while in aldehydes at least one hydrogen is attached to the carbon.
• Nomenclature of Aldehydes and Ketones
i. Some Common Names Aldehydes and Ketones
•ii. IUPAC Names of Aldehydes
Select the longest carbon chain containing the carbonyl carbon.
The -e ending of the parent alkane name is replaced by the suffix
The carbonyl carbon is always numbered “1.” (It is not
necessary to include the number in the name.)
Name the substituents attached to the chain in the usual way.
IUPAC : 2-pentanone 3-diethyl-2-heptanone
Physical Properties of Aldehydes and Ketones
In general, aldehydes and ketones have higher boiling points than
alkenes because they are more polar and the dipole–dipole attractive
forces between molecules are stronger.
But they have lower boiling points than alcohols because, unlike
alcohols, two carbonyl groups can’t form hydrogen bonds to each
Aldehydes and ketones can form hydrogen bonds with the protons
of OH groups.
This makes them more soluble in water than alkenes, but less
soluble than alcohols.
Carboxylic Acids and Their Derivatives
• the presence of at least one carboxyl group (-COOH).
• The general formula of a carboxylic acid is R-COOH OR
• A carboxyl group (-COOH) is a functional group consisting
of a carbonyl (C=O) and a hydroxyl (-OH).
• They are weak acids.
Nomenclature of Carboxylic Acids
i. Common system
• The common names are usually derived from the Latin or
Greek word that indicates the original source of the acid.
They do not follow any rule except that all common names
of acids end in –ic acid.
ii. IUPAC system
Simple carboxylic acids derived from open-chain alkanes are
systematically named by replacing the terminal -e of the
corresponding alkane name with -oic acid.
The -CO2H carbon atom is numbered C-1.
• Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic
• Aromatic acids are named as benzoic acids.
HCOOH Formic acid
CH3COOH Acetic acid
CH3CH2CH2 COOH Butyric acid
CH3(CH2)4COOH Caproic acid
Physical properties of carboxylic acids
Lower carboxylic acids (up to C-10) are liquids with sharp or
disagreeable odor. Higher members are wax-like solids and almost
• They have sour taste.
Carboxylic acids have higher boiling points than alcohols of
similar molecular weight.
• Smaller carboxylic acids (1 to 5 carbons) are soluble in water,
whereas higher carboxylic acids are less soluble.
Chemical properties of carboxylic acids
• In the presence of an acid catalyst, carboxylic acids and alcohols
react to form esters.
• The reaction is an equilibrium process but can be driven to favor
the ester by removing the water that is formed.
2. Formation of acyl chlorides
Thionyl chloride reacts with carboxylic acids to yield acyl
Reduction of Carboxylic Acids
• Carboxylic acids are reduced to primary alcohols by the powerful
reducing agent lithium aluminum hydride.
• The most widespread of all naturally occurring compounds.
• Many simple esters are pleasant-smelling liquids that are
responsible for the fragrant odors of fruits and flowers.
• They are result from the combination of a carboxylic acid with an
First identifying the alkyl group attached to oxygen and then the -
ic acid ending replaced by-ate or oate.
Ethyl butanoate Isopentyl acetate Isopentyl pentanoate Dimethyl malonate
(isolated from mangoes) (used in synthetic banana flavor) (used in synthetic apple flavor)
• resulting from the replacement of the -OH of a carboxylic acid with
• 1o (Amides with an unsubstituted -NH2 group) are named by
replacing the -oic acid or -ic acid ending with -amide, or by
replacing the -carboxylic acid ending with -carboxamide.
• The substituents are preceded by the letter N-(for 2o) or N,N- (3o) to
identify them as being directly attached to nitrogen.
-NHR (2o amide), or
-NR2 (3o amide) group.
• Cyclic esters and amides are called lactones and lactams,