Unit-2

Nomenclature

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 organic compounds are grouped into classes based on their
functional groups.
 A functional group is an atom or a group of atoms within a
molecule that serves as a site of chemical reactivity.

The most important functional groups are shown in the

following table,

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 Hydrocarbons are compounds that only contain carbon and
hydrogen atoms, and they can be classified as follows depending on
the bond types that are present within the molecules.

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Nomenclature of alkanes
 Alkanes are hydrocarbons having no double or triple bond .
 have the general molecular formula CnH2n+2 and are called saturated hydrocarbons.

 Saturated hydrocarbons contain only single bonds, and are also commonly
referred to as aliphatic or acyclic alkanes (alkanes without rings).
 Thus, the alkane family is characterized by the presence of tetrahedral carbon
(sp3) atoms. Methane (CH4) and ethane (C2H6) are the first two members of the
alkane family.

 A group derived from an alkane by removal of one of its hydrogen atoms is known
as an alkyl group, for example the methyl group (CH3--) from methane (CH4) and
the ethyl group (CH3CH2--) from ethane (CH3CH3).

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In general, organic compounds are given systematic names
by using the order:

prefix–parent–suffix
Where:
 prefix indicates how many branching groups are present,
 parent indicates how many carbons are in the longest
chain and
 suffix indicates the name of the family.

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The systematic name of an alkane is obtained using the following rules:

1. Determine the number of carbons in the longest continuous carbon chain. This chain is
called the parent hydrocarbon.

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2. Number the chain so that the substituent gets the lowest possible number

3. If more than one substituent is attached to the parent hydrocarbon, the chain
is numbered in the direction that will result in the lowest possible number in the
name of the compound. The substituents are listed in alphabetical (not
numerical) order, with each substituent getting the appropriate number. A
number and a word are separated by a hyphen; numbers are separated by
a comma.

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 If two or more substituents are the same, the prefixes “di,” “tri,” and “tetra”
are used to indicate how many identical substituents the compound has.

The prefixes di, tri, tetra, sec, and tert are ignored in alphabetizing substituent
groups, but the prefixes iso, neo, and cyclo are not ignored.

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4. When both directions lead to the same lowest number for one of the
substituents, the direction is chosen that gives the lowest possible number to one
of the remaining substituents.

5. If the same substituent numbers are obtained in both directions, the first group
cited receives the lower number.

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6. If a compound has two or more chains of the same length, the parent hydrocarbon
is the chain with the greatest number of substituents.

Some substituents have only a systematic name.

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Nomenclature of Cycloalkanes
 Cycloalkanes are alkanes with their carbon atoms arranged in a ring.
 have two fewer hydrogens than an acyclic (noncyclic) alkane with the same
number of carbons.
 are named by adding the prefix “cyclo” to the alkane name that signifies the
number of carbon atoms in the ring.

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The rules for naming cycloalkanes resemble the rules for naming acyclic alkanes:

1. In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent
hydrocarbon unless the substituent has more carbon atoms than the ring. In that case,
the substituent is the parent hydrocarbon and the ring is named as a substituent. There
is no need to number the position of a single substituent on a ring.

2. If the ring has two different substituents, they are cited in alphabetical order and
the number 1 position is given to the substituent cited first.

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3. If there are more than two substituents on the ring, they are cited in alphabetical
order. The substituent given the number 1 position is the one that results in a second
substituent getting as low a number as possible.

If two substituents have the same low number, the ring is numbered—either
clockwise or counterclockwise—in the direction that gives the third substituent the
lowest possible number.

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 CH3
1

CH3
2 H3C 3 1 CH3

1,2-Dimethylcyclopentane 1,3-Diethylcyclohexane
not 1,5-dimethylcyclopentane not 1,5-diethylcyclohexane

CH3
CH3 1 3 7
2 9
1 CH3 5
2 4 6 8

1,1,2-Trimethylcyclohexane 5-Cyclopentyl-4-methylnonane
not 1,2,2-Trimethylcyclohexane not 5-Cyclopentyl-6-methylnonane

Give the IUPAC name for each of the following compounds:

H3C
b) c)
a)
H3C CH2CH3

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Nomenclature of Alkyl Halides

 Formed when a hydrogen of an alkane is replaced by a halogen.

 classified as primary, secondary, or tertiary, depending on the carbon to which the
halogen is attached.
Primary alkyl halides have a halogen bonded to a primary carbon,
secondary alkyl halides have a halogen bonded to a secondary carbon, and
tertiary alkyl halides have a halogen bonded to a tertiary carbon.

The common names of alkyl halides consist of the name of the alkyl group followed
by halide (i.e., fluoride, chloride, bromide, iodide).

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In the IUPAC system, alkyl halides are named as substituted alkanes: Haloalkanes.

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Nomenclature of Alkenes
The systematic (IUPAC) name of an alkene is obtained by replacing the “ane”
ending of the corresponding alkane with “ene.”

Most alkene names need a number to indicate the position of the double bond.
1. Number the longest continuous chain containing the functional group in the
direction that gives the functional group suffix the lowest possible number

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2. The name of a substituent is cited before the name of the longest continuous chain
containing the functional group, together with a number to designate the carbon to
which the substituent is attached. Notice that the chain is still numbered in the
direction that gives the functional group suffix the lowest possible number.

3. If the same number for the alkene functional group suffix is obtained in both
directions, the correct name is the name that contains the lowest substituent
number.

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4. In cyclic alkenes, a number is not needed to denote the position of the functional
group, because the ring is always numbered so that the double bond is between
carbons 1 and 2.

5. If both directions lead to the same number for the alkene functional group suffix
and the same low number(s) for one or more of the substituents, then those
substituents are ignored and the direction is chosen that gives the lowest number to
one of the remaining substituents.

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Draw the structure for each of the following compounds:

a. 3,3-dimethylcyclopentene b. 6-bromo-2,3-dimethyl-2-hexene

Give the systematic name for each of the following compounds:

Give the IUPAC name for each of the following compounds:

Br
CH3CH2 CH3
a) CH3CHCH2CH=CCH2CHCH3 b)

CH3 CH2CH3

CH CH2CH2CH2CH CH CH CH2 c)
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Nomenclature of Alkynes
Alkynes are hydrocarbons that contain a carbon–carbon triple bond. A triple bond consists
of a  bond and two  bonds. The general formula for the alkynes is CnH2n-2.

Terminal CH groups are called acetylenic hydrogens. If the triple bond has two alkyl groups
on both sides, it is called an internal alkyne
CHCH CH3CH2CCH CH3CH2CCCH3
4 3 2 1 5 4 3 21
Ethyne (acetylene) 1-Butyne (ethylacetylene) 2-Pentyne (ethylmethylacetylene)
Terminal alkyne Internal alkyne

The IUPAC nomenclature of alkynes is similar to that for alkanes, except the –ane ending
is replaced with –yne.
CH3 CH3 Br

CH3CCCHCH2CH3 CH3CHCCCHCH2CH3 (CH3)3CCCCH3

1 2 3 4 5 6 1 2 3 4 5 6 7

4-Methyl-2-hexyne 5-Bromo-2-methyl-3-heptyne 4,4-Dimethyl-2-pentyne

Question
Write structural formulas and give the IUPAC names for all the alkynes of molecular formula
C5H04/14/2024
8. 24
Classification of carbon substitution: A carbon atom is classified as primary (1°),
secondary (2°), tertiary (3°) and quaternary (4°) depending on the number of carbon atoms
bonded to it.

Primary carbon

Primary carbon CH3 CH3

H3C CH2 CH2 CH C CH3

CH3 Quaternary carbon

Tertiary
carbon
Secondary carbon Primary
carbon

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 Alcohols
The functional group of an alcohol is the hydroxyl (OH) group. Therefore, an alcohol has
the general formula ROH. The simplest and most common alcohols are methyl alcohol
(CH3OH) and ethyl alcohol (CH3CH2OH).

An alcohol may be acyclic or cyclic. It may contain a double bond, a halogen atom or
additional hydroxyl groups. Alcohols are usually classified as primary (1°), secondary (2°) or
tertiary (3°).
H H H
OH
CH3CH2 C OH H3C C OH H3C C OH

H CH3 CH3
Propanol Isopropanol tert-Butanol Phenol
Propyl alcohol (1) 2-Propanol (2) 2-Methyl-2-propanol (3)

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Nomenclature of Alcohols

Generally, the name of an alcohol ends with -ol. An alcohol can be named as an alkyl alcohol,
usually for small alkyl groups e.g. methyl alcohol and ethyl alcohol. The longest carbon chain
bearing the OH group is used as the parent; the last -e from this alkane is replaced by an -ol
to obtain the root name.
CH3 OH OH HO CH2CH2CH3
H3CCHCHCH2Br CH3CH2CHCH2CH2Cl
4 3 2 1 5 4 3 2 1

1-Bromo-3-methyl-2-butanol 1-Chloro-3-pentanol 1-Propylcyclopentanol

(The OH is at C-2 of butane) (The OH is at C-3 of pentane)

OH
OH 1
OH
5 3
CH3CH2CHCH2CO2H H2C=CHCH2CHCH3
5 4 3 2 1 5 4 3 2 1 Cl Br

3-Hydroxypentanoic acid Pent-4-en-2-ol 3-Bromo-5-chlorocyclohexanol

2
OH
1 1 2 3 6 2
CH2CH2 CH2CHCH3 4
3 1
5
OH OH OH OH OH
1,2-Ethane diol 1,2-propane diol 3,4-Hexanediol
(Ethylene glycol)
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 Name the following compounds according to the IUPAC system :

OH

a) b) c)

OH OH

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Ethers
Ethers are also organic relatives of water, where alkyl groups replace both hydrogen atoms.
Thus, ethers have two hydrocarbons bonded to an oxygen atom. The simplest and most
common ethers are diethyl ether and tetrahydrofuran (THF), which is a cyclic ether.
O

C2H5OC2H5

Diethyl ether Tetrahydrofuran

(Ether) (THF)
Ethers are relatively unreactive towards most reagents, so they are frequently used as
solvents in organic reactions. A few other common ether solvents are shown below.
CH3
O
CH3OCH2CH2OCH3 CH3OCCH3
1,2-Dimethoxyethane CH3 O
(DME)
Methyl tert-butyl ether 1,4-Dioxane
(MTBE)

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Nomenclature of Ethers

Ethers can be symmetrical, where the two alkyl groups are the same, or unsymmetrical,
where the two alkyl groups are different

H3COCH3 H3COC2H5

Dimethylether (symmetrical) Ethyl methyl ether (unsymmetrical)

In the nomenclature of ethers, either the suffix -ether or the prefix alkoxy- is used.
CH3
C2H5OC2H5 CH3OCCH3

Diethyl ether CH3

(Ethoxyethane) Methyl tert-butyl ether
(2-Methyl-2-methoxypropane)

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Three membered cyclic ethers are known as epoxides. They are just a subclass of ethers
containing a three-membered oxirane ring (COC unit). Cyclic ethers have the prefix
epoxy- and suffix -alkene oxide. Five membered and six membered cyclic ethers are known
as oxolane and oxane, respectively.

H2C CH2 CH3CH CH2 CH3CH2CH CH2

O O O

Ethylene oxide Propylene oxide Butylene oxide

(Epoxy ethane) (1,2-Epoxy propane) (1,2-Epoxy butane)

O O O

O
Oxirane ring (epoxide) Oxolane (THF) Oxane

Question
Write the structure of each of the following ethers.
(a) Chloromethyl methyl ether
(b) 2-(Chloromethyl)oxirane
(c) 3,4-Epoxy-1-butene (2-vinyloxirane)
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Amines
Amines are nitrogen containing compounds, the functional group is an amino group (NH2).
They are organic relatives of ammonia, where one or more of the hydrogen atoms of
ammonia are replaced by alkyl group(s)

Amines are classified as primary (1°), secondary (2°), tertiary (3°) or quaternary (4°)
depending on how many alkyl groups are attached to the N atom.

CH3 CH3
CH3CH2CH2NH2 CH3NHCH3 CH3NCH3 CH3NCH3
Propylamine Dimethylamine Trimethylamine CH3
(1 amine) (2 amine) (3 amine)
Tetramethylamine
(4 amine)
Aliphatic amines are named according to the alkyl group or groups attached to nitrogen
with the suffix -amine CH 3

H2NCH2CH2NH2 C2H5NHCH3 CH3NHCH(CH2)3CH3

Ethylenediamine Methylethylamine 2-(N-Methylamino)hexane

(1° amine) (2° amine) (2 amine)

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If other substituents are attached to the nitrogen atom, they are indicated by the prefix N-
before the name of the substituents. The simplest aromatic amine is aniline (C 6H5NH2),
where nitrogen is attached directly to a benzene ring.

Provide a structural formula for each of the following compounds:

(a) 2-Ethyl-1-butanamine (b) N-Ethyl-1-butanamine
(c) Tetraethylammonium hydroxide (d) N-Allylcyclohexylamine
(e) 2,2-Dimethyl-1,3-propanediamine

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Aldehydes and Ketones

A carbonyl functional group (C=O) is a carbon double bonded to an oxygen atom. An acyl
functional group (RC=O) consists of a carbonyl group attached to an alkyl or an aryl group.

O O

C
R C

Carbonyl group Acyl group (R = alkyl or aryl)

O O O

H C H H3C C H H3C C CH3

Formaldehyde Ethanal Propanone

Acetaldehyde Acetone

In the IUPAC nomenclature of

Aldehydes, the -e of the alkane is replaced with -al, e.g. ethanal (the parent alkane is
ethane).
Ketones are named by replacing the -e ending of the alkyl name with -one, e.g. propanone
(the parent alkane is propane).

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If the aldehyde group is a substituent on a ring, the suffix -carbaldehyde is used in the name.
O CH
3
O H3C C CCH3
Cl O
H CH3
Cyclohexanecarbaldehyde 3-Methyl-2-butanone 4-Chlorocyclohexanone

An aldehyde or ketone group can also be named as a substituent on a molecule with

another functional group as its root.
The aldehyde carbonyl is given the prefix formyl-, and the ketone group is named oxo-
with a number to show its position in the molecule.

O O O O O

C2H5 C CH2CH H3C C CH2CH H3C C CH2CH2H

3-Oxopentanal 3-Oxobutanoic acid 4-Hydroxy-2-butanone

O
O O
CH
C C
CH3
COH
O Acetophenone Benzophenone
2-Formylbenzoic acid

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Write a structural formula for each of the following.
(a) 2,2,2-trichloroethanal (b) 2,2-dimethylpropanal
(c) (E)-2-butenal (d) 4-hydroxy-4-methyl-2-pentanone

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Carboxylic Acids
Carboxylic acid is an organic acid that has an acyl group (RC=O) linked to a hydroxyl group (OH).
In a condensed structural formula, a carboxyl group may be written as CO2H, and a carboxylic acid as
RCO2H.
O O

COH R COH
CO2H or COOH RCO2H or RCOOH

Carboxyl group Carboxylic acid

O
O O
COH
HCOH H3C COH
Methanoic acid Ethanoic acid Benzenecarboxylic acid
Formic acid Acetic acid Benzoic acid

The root name is based on the longest continuous chain of carbon atoms bearing the carboxyl
group. The -e is replaced by -oic acid. The chain is numbered starting with the carboxyl
carbon atom.

The carboxyl group takes priority over any other functional groups as follows: carboxylic acid
> ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne.

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 O O O

CH3CH2COH CH3CH2CH2COH CH3CH2CH2CH2COH

Propanoic acid Butanoic acid Pentanoic acid
Propionic acid Butyric acid Valeric acid

O O O
H2N
H2C=CHCOH CH3CH2CHCOH OH
Propenoic acid OMe
Acrylic acid 2-Methoxybutanoic acid 4-Aminobutanoic acid

Cycloalkanes with carboxyl substituents are named as cycloalkanecarboxylic acids.

Unsaturated acids are named using the name of the alkene with -e replaced with -oic acid.
O
HOCCHCH3 CO2H
C2H5 H

CH3 H3C CH2CO2H

2-Cyclohexylpropanoic 3-Methylcyclohexanecarboxylic (E)-4-Methyl-3-hexenoic acid
acid acid

Aliphatic dicarboxylic acids are named by simply adding the suffix –dioic acid to the root
name. Br O
HO
OH
O Br

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Provide a structural formula for each one on the basis of its systematic name.
(a) 2-Hydroxy-2-phenylethanoic acid
(b) (b) 10-Undecenoic acid
(c) 3,5-Dihydroxy-3-methylpentanoic acid
(d) (E)-2-Methyl-2-butenoic acid
(e) 2-Hydroxy-1,2,3-propanetricarboxylic acid
(f) 2-(p-Isobutylphenyl)propanoic acid

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Carboxylic Acid Derivatives

Carboxylic acid derivatives are compounds that possess an acyl group (RC=O) linked to an
electronegative atom, e.g. Cl, CO2R, OR or NH2.

They can be converted to carboxylic acids via simple acidic or basic hydrolysis.

The important acid derivatives are acid chlorides, acid anhydrides, esters and amides.
O O O O O
R C Cl R C OCR R C OR RCNHR
Acid chloride Acid anhydride Ester Amide
RCOCl (RCO)2O RCO2R RCONH2

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Nomenclature of Acid Chlorides
Acid chlorides are named by replacing the -ic acid ending with -yl chloride or replacing the
carboxylic acid ending with -carbonyl chloride.

O O O

CH3CCl CH3CH2CCl CH3CH2CH2CCl

Ethanoyl chloride Propanoyl chloride Butanoyl chloride
Acetyl chloride

O Br O O O

CH3CH2CH2CH2CCl CH3CH2CHCCl
Cl
Cl
Pentanoyl chloride 3-Bromobutanoyl chloride Cyclohexanecarbonyl Benzoyl chloride
chloride

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 Acid Anhydrides

The functional group of an acid anhydride is two acyl groups bonded to an oxygen atom.
These compounds are called acid anhydrides or acyl anhy­drides, because they are condensed
from two molecules of carboxylic acid by the loss of a water molecule.

O O O O

H3 C C OCCH3 H3 C C OCCH2CH3

Ethanoic anhydride Acetic propanoic anhydride

Acetic anhydride

Symmetrical acid anhydrides are named by replacing the -acid suffix of the parent carboxylic
acids with the word anhydride.

Mixed anhydrides that consist of two different acid-derived parts are named using the names
of the two individual acids with an alphabetical order.
O O O O

CH3CH2 C OCCH2CH3 CH3CH2 C OCCH2CH2CH3

Propanoic anhydride Butanoic propanoic anhydride

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Esters
The functional group of an ester is an acyl group bonded to an alkoxy group (OR).

O O O
H3CCOCH3 H3CCOCH2CH3 H3CCOCH2CH2CH3
Methyl acetate Ethyl acetate Propyl acetate
Methylethanoate Ethylethanoate Propylethanoate
The names of esters originate from the names of the compounds that are used to prepare them.
The first word of the name comes from the alkyl group of the alcohol, and the second part comes from the
carboxylate group of the carboxylic acid used.

A cyclic ester is called a lactone, and the IUPAC names of lactones are derived by adding the term lactone
at the end of the name of the parent carboxylic acid.

O O

CH3CH2COCH2(CH3)2CH3 H3CCOCH2CH2CH(CH3)2
Butyl propanoate Isopentyl acetate

O O O

OC(CH3)3 OC2H5
O

t-Butylcyclohexanecarboxylate Ethyl benzoate 4-Hydroxybutanoic acid lactone

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Amides
The functional group of an amide is an acyl group bonded to a nitrogen atom. The simplest
members of this family are formamide (HCONH2) and acetamide (CH3CONH2).
O O O
HCNH2 H3CCNH2 C2H5CNH2
Methanamide Ethanamide Propanamide
Formamide Acetamide

Amides are usually classified as primary (1°) amide, secondary (2°) or N-substituted amide, and tertiary
(3°) or N,N-disubstituted amide.

O O O
RCNH2 RCNHR RCNR2
Primary amide Secondary (2) or Tertiary (3) or
(1 N-substituted amide N,N-disubstituted amide

Amides are named by replacing the -oic acid or -ic acid suffix of the parent carboxylic acids with the suffix
-amide, or by replacing the -carboxylic acid ending with -carboxamide. Alkyl groups on nitrogen atoms are
named as substituents, and are prefaced by N-or N,N-, followed by the name(s) of the alkyl group(s).

O O
O O
CNH2 CNH2
H3CCNHCH2CH3 HCN(CH3)2
N-Ethylethanamide N,N-Dimethylformamide Cyclohexanecarboxamide Benzamide
DMF

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Provide a structural formula for each of the following compounds:
a) 3,3-dimethylheptanoic acid b) 3-chloro-1,1-cyclopentanedicarboxylic
acid
c) 4-methyl-3-pentenoyl chloride d) Ethyl para-methoxybenzoate
e) N,N-dimethyl-2-ethylbutanamide

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