Unit-2
Nomenclature
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1
 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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2
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3
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4
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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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1
CH3
2
CH3
H3C
1,2-Dimethylcyclopentane
not 1,5-dimethylcyclopentane
1
3
CH3
1,3-Diethylcyclohexane
not 1,5-diethylcyclohexane
CH3
CH3
2
1 CH3
7
3
1
2
4
5
6
9
8
5-Cyclopentyl-4-methylnonane
not 5-Cyclopentyl-6-methylnonane
1,1,2-Trimethylcyclohexane
not 1,2,2-Trimethylcyclohexane
Give the IUPAC name for each of the following compounds:
a)
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b)
H3C
H3C
c)
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
a) CH3CHCH2CH=CCH2CHCH3
CH3
b)
CH2CH3
CH3CH2CH2CH2CH
c)
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CH3
CH
CH
CH2
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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
CH3CH2CCH
CHCH
4
Ethyne (acetylene)
CH3CH2CCCH3
2 1
3
5
4
3 21
2-Pentyne (ethylmethylacetylene)
Internal alkyne
1-Butyne (ethylacetylene)
Terminal alkyne
The IUPAC nomenclature of alkynes is similar to that for alkanes, except the –ane ending
is replaced with –yne.
CH3
CH3
CH3CCCHCH2CH3
1
2 3 4
5
6
4-Methyl-2-hexyne
Br
CH3CHCCCHCH2CH3
1
2
3 4 5
6
(CH3)3CCCCH3
7
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
C5H2/4/2023
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
H3C
CH2
CH2
CH3
CH3
CH
C
Tertiary
carbon
Secondary carbon
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CH3
CH3
Quaternary 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
CH3CH2
C
OH
H
Propanol
Propyl alcohol (1)
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H3C
C
H
OH
CH3
Isopropanol
2-Propanol (2)
H3C
C
OH
OH
CH3
tert-Butanol
2-Methyl-2-propanol (3)
Phenol
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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
H3CCHCHCH2Br
4
2
3
1
1-Bromo-3-methyl-2-butanol
(The OH is at C-2 of butane)
HO
CH2CH2CH3
CH3CH2CHCH2CH2Cl
5
2
3
4
1
1-Propylcyclopentanol
1-Chloro-3-pentanol
(The OH is at C-3 of pentane)
OH
CH3CH2CHCH2CO2H
5
4
2
3
1
3-Hydroxypentanoic acid
1
1
OH
OH
2
5 4
3
2
Pent-4-en-2-ol
1
2
3
CH2CHCH3
OH
OH
1,2-Ethane diol
(Ethylene glycol)
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OH
1,2-propane diol
(Propylene glycol)
3
Cl
1
CH2CH2
OH
5
H2C=CHCH2CHCH3
Br
3-Bromo-5-chlorocyclohexanol
OH
6
5
4
3
2
1
OH
3,4-Hexanediol
27
Name the following compounds according to the IUPAC system:
OH
a)
OH
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c)
b)
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
(Ether)
Tetrahydrofuran
(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
CH3OCH2CH2OCH3
1,2-Dimethoxyethane
(DME)
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CH3OCCH3
O
CH3
O
Methyl tert-butyl ether
(MTBE)
1,4-Dioxane
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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
Diethyl ether
(Ethoxyethane)
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CH3OCCH3
CH3
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
CH2
CH3CH2CH
O
O
O
Ethylene oxide
(Epoxy ethane)
Propylene oxide
(1,2-Epoxy propane)
Butylene oxide
(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
CH3CH2CH2NH2
Propylamine
(1 amine)
CH3NHCH3
CH3NCH3
Dimethylamine
(2 amine)
Trimethylamine
(3 amine)
CH3
CH3NCH3
CH3
Tetramethylamine
(4 amine)
Aliphatic amines are named according to the alkyl group or groups attached to nitrogen with
the suffix -amine
CH3
H2NCH2CH2NH2
Ethylenediamine
(1° amine)
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C2H5NHCH3
Methylethylamine
(2° amine)
CH3NHCH(CH2)3CH3
2-(N-Methylamino)hexane
(2 amine)
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If other substituents are attached to the nitrogen atom, they are indicated by the prefix Nbefore the name of the substituents. The simplest aromatic amine is aniline (C6H5NH2),
where nitrogen is attached directly to a benzene ring.
Provide a structural formula for each of the following compounds:
(a) 2-Ethyl-1-butanamine
(c) Tetraethylammonium hydroxide
(e) 2,2-Dimethyl-1,3-propanediamine
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(b) N-Ethyl-1-butanamine
(d) N-Allylcyclohexylamine
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Nitriles
a triple bond between a carbon and a nitrogen atom. The functional group in nitriles is the
cyano (C≡N) group, and they are often named as cyano compounds.
H3CCN
CH3CH2CN
Ethanenitrile
Acetonitrile
Propanenitrile
The IUPAC requires nitriles to be named on the basis of the name of the alkanes, with the
suffix -nitrile.
OCH3
CN
Benzonitrile
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H3CCHCH2CH2CH2CN
5-Methoxyhexanenitrile
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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
Carbonyl group
R
Acyl group (R = alkyl or aryl)
O
O
H
C
C
H
Formaldehyde
H3C
C
O
H
Ethanal
Acetaldehyde
H3C
C
CH3
Propanone
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
CH3
H
4-Chlorocyclohexanone
3-Methyl-2-butanone
Cyclohexanecarbaldehyde
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 oxowith a number to show its position in the molecule.
O
C2H5
C
O
CH2CH
3-Oxopentanal
O
CH
H3C
O
O
C
CH2CH
3-Oxobutanoic acid
H3C
C
CH2CH2H
4-Hydroxy-2-butanone
O
O
C
O
CH3
C
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
(c) (E)-2-butenal
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(b) 2,2-dimethylpropanal
(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
Carboxylic acid
Carboxyl group
O
O
O
HCOH
H3C COH
Methanoic acid
Formic acid
Ethanoic acid
Acetic acid
COH
Benzenecarboxylic 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
CH3CH2CH2CH2COH
CH3CH2CH2COH
Propanoic acid
Propionic acid
Pentanoic acid
Valeric acid
Butanoic acid
Butyric acid
O
O
O
H2C=CHCOH
CH3CH2CHCOH
Propenoic acid
Acrylic acid
OMe
H2N
2-Methoxybutanoic acid
OH
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
CO2H
HOCCHCH3
CH3
2-Cyclohexylpropanoic
acid
3-Methylcyclohexanecarboxylic
acid
C2H5
H
H3C
CH2CO2H
(E)-4-Methyl-3-hexenoic acid
Aliphatic dicarboxylic acids are named by simply adding the suffix –dioic acid to the root
name.
Br O
HO
OH
O
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Br
3,4-Dibromohexanedioic acid
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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
R
C
Cl
Acid chloride
RCOCl
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R
O
O
C
OCR
Acid anhydride
(RCO)2O
O
R
C
O
OR
Ester
RCO2R
RCNHR
Amide
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
Acetyl chloride
Propanoyl chloride
Butanoyl chloride
O
CH3CH2CH2CH2CCl
Pentanoyl chloride
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Br
O
CH3CH2CHCCl
O
O
Cl
Cl
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.
H3C
C
O
O
O
OCCH3
Ethanoic anhydride
Acetic anhydride
H3C
C
O
OCCH2CH3
Acetic propanoic 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
CH3CH2
C
OCCH2CH3
Propanoic anhydride
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O
CH3CH2
C
O
OCCH2CH2CH3
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
H3CCOCH3
O
H3CCOCH2CH3
H3CCOCH2CH2CH3
Ethyl acetate
Ethylethanoate
Methyl acetate
Methylethanoate
Propyl acetate
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
Butyl propanoate
Isopentyl acetate
O
O
OC(CH3)3
t-Butylcyclohexanecarboxylate
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H3CCOCH2CH2CH(CH3)2
O
OC2H5
Ethyl benzoate
O
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
Formamide
Ethanamide
Acetamide
Propanamide
Amides are usually classified as primary (1°) amide, secondary (2°) or N-substituted amide, and tertiary
(3°) or N,N-disubstituted amide.
O
O
RCNH2
Primary amide
(1
O
RCNHR
RCNR2
Secondary (2) or
N-substituted amide
Tertiary (3) or
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
H3CCNHCH2CH3
N-Ethylethanamide
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O
O
CNH2
CNH2
O
HCN(CH3)2
N,N-Dimethylformamide Cyclohexanecarboxamide
DMF
Benzamide
45
Provide a structural formula for each of the following compounds:
a) 3,3-dimethylheptanoic acid
c) 4-methyl-3-pentenoyl chloride
e) N,N-dimethyl-2-ethylbutanamide
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b) 3-chloro-1,1-cyclopentanedicarboxylic acid
d) Ethyl para-methoxybenzoate
46