Download Organic Nomenclature

Organic Nomenclature
Organic compounds are compounds containing carbon bonded to other
nonmetals such as hydrogen, nitrogen, oxygen, or the halogens. The term organic comes
from the old idea that all carbon containing compounds had to be produced by a living
organism. While living organisms produce a vast number of organic compounds, many of
these compounds, as well as many compounds not found in nature, can be produced in
the laboratory. Since carbon can form single, double, and triple bonds, and can form
chains of carbon atoms bonded to each other, a wide variety of organic compounds can
be formed. The name of the compound must be systematic in order to provide enough
information to derive a chemical structure from the name or a name from the structure.
Organic nomenclature is complicated by the fact that the same compound may have a
standard IUPAC (International Union of Pure and Applied Chemistry) name and a
common name that came from previous nomenclature systems or the original source of
the compound. Often the common name is more frequently used than the standard name.
While we will show some of the common names for reference, you will only be
responsible for the standard name.
Organic nomenclature is structured on the concept of different classes of
compounds. Each class of compounds contains a group of atoms that defines that class of
compound and controls their reactions. This group of atoms is called the functional group
of the compound. The name of the compound is derived from the stem name for the
longest continuous chain of carbon atoms in the molecule and a suffix for the functional
group.
The prefixes for the length of the carbon chain are shown in the table below.
Number of Carbon Atoms
1
2
3
4
5
6
7
8
9
10
11
12
Stem Name
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
Undec
Dodec
Side Chain Name
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Nonyl
Decyl
Undecyl
Dodecyl
Hydrocarbons
Hydrocarbons are compounds that contain only carbon and hydrogen atoms.
There may be single or multiple bonds present.
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Hydrocarbons
Compound
Alkane
Alkene
Alkyne
Alkadienes
Cycloalkane
General Formula
CnH2n+2
CnH2n
CnH2n-2
CnC2nCnH2n
Arenes
ArH
Example
CH3CH2CH3
CH3CH=CH2
Name
propane
propene
2-butyne
1,3-butadiene
cyclohexane
benzene
Alkanes
Alkanes are sometimes referred to as saturated hydrocarbons since they have only
single bonds. There are no additional electrons available for bonding so the molecule is
“saturated” with atoms. The suffix for alkanes is ane. We will use alkanes as the model
for several of the general rules of organic nomenclature.
1. Choose the longest continuous chain of carbon atoms. Use the stem name for the
longest chain and add ane.
The longest continuous chain of carbon atoms may not always be written horizontally so
you need to check the molecule carefully. In the structures below, the longest chain is six.
2. There may be hydrocarbon groups of atoms attached to the main carbon chain. These
groups are called side chains. The name of the side chain is based on the number of
carbons in the side chain and its name ends in -yl. Side chains are often called alkyl
groups. The common unbranched side chain names are listed in the table above.
If there are side chains in the molecule, number the carbons from the end that gives the
side chain the lowest number. Once you start to number from a specific end of the chain,
continue numbering down the chain from that end. The side chain is assigned the number
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of the carbon of the main chain to which it is attached. The compound may be drawn
differently but will have the same name.
If the chain is short enough so that there is no doubt about the position of the side chain, a
number is not used with the side chain.
3. If there are several side chains in the molecule, the number of the position of each side
chain is included. If several of the same side chains are present, the prefixes di, tri, tetra,
penta, hexa, etc. are attached to the name of the side chain. The side chains are listed in
alphabetical order regardless of their number position or any prefixes attached to the
name of the side chain. Halogen atoms are considered to be side chains and the names
fluoro (F), chloro (Cl), bromo (Br), and iodo (I) are used.
(This is not 6-ethyl-7-ethylnonane. Start the numbering from the left so the side chains
have lower numbers.)
(Start the numbering from the right.)
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There are several branched side chains that have common names. The more
important ones are shown below. The prefix iso refers to a side chain with a methyl group
on the second carbon starting at the end of the chain opposite the point of attachment.
The standard name for these side chains chooses the longest continuous chain in carbon
atoms in the side chain as the base name and then numbers and names the groups
attached to it with the number one carbon being the point of attachment. The standard
name and common name of some branched side chains are shown below.
Side Chain
Standard Side Chain Name
1-methylethyl
Common Side Chain Name
Isopropyl
2-methylpropyl
Isobutyl
1-methylpropyl
Sec-butyl
1,1-dimethylethyl
Tert-butyl
3-methylbutyl
Isopentyl
Cycloalkanes
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Carbon atoms can form rings as well as open chain molecules. The name is based
on the number of carbons in the ring. The carbon atoms in the ring are numbered so the
substituents have the lowest numbers.
Alkenes
Alkenes contain a double bond and are referred to as unsaturated hydrocarbons.
The π electrons could be available for bonding additional atoms. The suffix for alkenes
is ene.
Choose the longest continuous carbon chain that contains the double bond.
Number the chain from the end that will give the double bond the lowest number. This
sets the direction and order of the numbering in the whole molecule. The number of the
double bond will be the number of the first carbon of the double bond starting from that
end of the chain. The side chains are numbered and named as with alkanes. If the chain is
short enough so that there is no doubt about the position of the double bond or the side
chain, numbers are not used.
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There are common names for some of the smaller alkenes using the side chain
names for the numbers of carbons present and adding ene. These names are still used in
industry and in naming the polymers made from these compounds. Polyethylene is the
material in plastic food wrap and polypropylene is used in sports clothing.
Cycloalkenes
The name is based on the number of carbons in the ring. The first carbon of the
double bond is assumed to be the number one carbon. The second carbon of the double
bond must be the number two carbon. The first double bond is not numbered. The carbon
atoms in the ring are numbered in the direction so the substituents have the lowest
numbers.
Alkadienes
A compound may contain more than one double bond and are called dienes,
trienes, etc. Choose the longest continuous carbon chain that contains the double bonds.
Number the chain from the end that will give the double bonds the lowest numbers. This
sets the direction and order of the numbering in the whole molecule.
Alkynes
Alkynes are unsaturated hydrocarbons containing a triple bond. The two sets of π
electrons could be available for bonding additional atoms. The suffix for alkynes is yne.
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Choose the longest continuous carbon chain that contains the triple bond. Number
the chain from the end that will give the triple bond the lowest number. This sets the
direction and order of the numbering in the whole molecule. The number of the triple
bond will be the number of the first carbon of the triple bond starting from that end of the
chain. The side chains are numbered and named as with alkanes. If the chain is short
enough so that there is no doubt about the position of the triple bond, a number are not
used for the triple bond.
The common name for ethyne is acetylene, a gas commonly used for welding.
Benzene compounds
The formula of benzene is shown below.
While it appears to be a cyclohexatriene, it does not chemically behave like an
alkene! The three π bonds simultaneously overlap to form a delocalized set of electrons
that produces additional stability in the molecule and significantly different chemical
properties. Benzene compounds are often referred to as aromatic compounds. The
nomenclature of benzene and other aromatic compounds is complicated since many
common names are used. We will consider only a few of the mono- and di-substituted
compounds here. The prefixes ortho (the two groups are adjacent to each other on the
ring), meta (the two groups are separated by one carbons), and para (the two groups are
separated by two carbons and are on opposite sides of the ring) are used in the common
names. The carbon atoms are numbered around the ring in the direction to give the
substituents smaller numbers. In the structures below, the standard name is written first
and the common name second.
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(Note: If the benzene ring is viewed as a side chain, it is called a phenyl group.)
The structures and names for some additional hydrocarbons are shown below. See if the
names make sense using the rules discussed above.
Structure
Standard Name (IUPAC)
butane
Common Name
2,2 dimethylhexane
4-ethyl-3-methyloctane
2,2,3-trichlorobutane
6-methyl-2-butene
1-butyne
2-butyne
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Functional Groups Containing Oxygen
Compound
Alcohol
Ether
Groups Containing Oxygen
General Formula
Example
Aldehyde
Name
ethanol
methoxyethane
(methyl ethyl ether)
ethanal (acetaldehyde)
Ketone
propanone
(dimethyl ketone)
Carboxylic acid
ethanoic acid
(acetic acid)
Ester
ethyl ethanoate
(ethyl acetate)
Alcohols
Alcohols are compounds that have an OH group (hydroxyl) bonded to
hydrocarbon chains. (If the OH group is bonded to a carbon in an aromatic ring, the
compound is a phenol and a different class of compound.) The OH group is covalently
bonded to the carbon so alcohols do not ionize to produce hydroxide ions, OH-. The
suffix for alcohols is ol.
Choose the longest continuous carbon chain that contains the OH group. Number
the chain from the end that will give the OH group the lowest number. This sets the
direction and order of the numbering in the whole molecule. The number of the OH
group will be the number of the carbon to which it is bonded. The side chains are
numbered and named as with alkanes. If the chain is short enough so that there is no
doubt about the position of the OH group, it is not given a number.
In the common naming system, the side chain name for that number of carbons
and the word alcohol was used. Methanol was methyl alcohol, ethanol was ethyl alcohol,
1-propanol was propyl alcohol (or n-propyl alcohol where n meant normal – all the
carbons bonded in a continuous chain), and 2-propanol was isopropyl alcohol (the
alcohol in rubbing alcohol).
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Ethers
Ethers are compounds with two hydrocarbon (saturated, unsaturated, or aromatic)
groups attached to an oxygen atom. The shorter chain group is given the suffix oxy and is
combined with the hydrocarbon name of the other group. Numbers are added if the
oxygen atom is not bonded to the end of each group.
The common naming system used the side chain name of each group (not
necessarily in alphabetical order) and the word ether. In the structures below, the standard
name is given first with the common name second.
Aldehydes
Aldehydes are the first member of the family of compounds that contain a
carbon atom double bonded to an oxygen atom, C=O, which is called a carbonyl group.
The aldehyde has one hydrocarbon group and one hydrogen atom attached to the
carbonyl group. The aldehyde group is
The suffix for aldehydes is al.
Choose the longest continuous carbon chain that contains the aldehyde group. The
aldehyde group must be at the end of the chain or it will not have a hydrogen atom
attached to the carbonyl group and will be a different functional group. The carbon of the
aldehyde group is the number one carbon and is not given a number in the name. This
sets the direction and order of the numbering in the whole molecule. The side chains are
numbered and named as with alkanes.
The common name of the aldehyde was based on the common name of the
carboxylic acid to which it could be oxidized and the word aldehyde was added. There is
no simple way to get from the standard name to the common name without knowing the
common names of the acids. Formaldehyde and acetaldehyde are still commonly used. In
the structures below, the standard name is given first with the common name second.
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Ketones
Ketones have two hydrocarbon groups attached to the carbonyl group,
C=O. The suffix for ketones is one.
Choose the longest continuous carbon chain that contains the C=O group.
Number the chain from the end that will give the C=O group the lowest number. This sets
the direction and order of the numbering in the whole molecule. The number of the C=O
group will be the number of the carbon of the carbonyl group. The side chains are
numbered and named as with alkanes. If the chain is short enough so that there is no
doubt about the position of the C=O group, it is not given a number.
The common naming system used the side chain name of each group (not necessarily in
alphabetical order) and the word ketone. In the structure below, the standard name is
given first with the common name second. In the case of propanone, acetone is the most
commonly used name for the compound and is derived from the fact that it can be
oxidized to acetic acid. In the structures below, the standard name is given first with the
common name second.
Carboxylic acids
Carboxylic acids have a hydrocarbon group attached to the carboxylic acid
group,
. The suffix for carboxylic acid is oic acid.
Choose the longest continuous carbon chain that contains the carboxylic acid
group. The carboxylic acid group must be at the end of the chain. The carbon of the
carboxylic acid group is the number one carbon and is not given a number in the name.
This sets the direction and order of the numbering in the whole molecule. The side chains
are numbered and named as with alkanes.
Many carboxylic acids occur in plants and animals. The common name of the
carboxylic acid was based on the natural source of the acid (often a derivative of a Latin
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name). Formic acid is found in ants and acetic acid is found in vinegar. In the structures
below, the standard name is given first with the common name second.
An NH2 group can be present as a substituent and is called an amino group. The
combination of the two groups forms the important biological family of compounds, the
amino acids.
Functional Derivatives of Carboxylic Acids
Additional classes of compounds are formed by the reaction of carboxylic acids
with other compounds. These are called functional derivatives of carboxylic acids.
Esters
Esters are formed by the reaction of a carboxylic acid and an alcohol. Esters
account for the odors of many flowers and fruits.
The group that came from the alcohol and is attached to the oxygen in the ester is named
first with the same name as a side chain and ends in yl. The rest of the molecule is named
in the same manner as the carboxylic acid except the ending is changed from oic acid to
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oate. The common name for the ester uses the common name for the acid. In the
structures below, the standard name is listed first with the common name second.
Amides
Amides are formed by the reaction of an acid chloride or acid anhydride and
ammonia (NH3), a primary amine (RNH2), or a secondary amine (R2NH).
There can be two hydrogen atoms, one hydrocarbon group, or two hydrocarbon groups
bonded to the nitrogen. If two hydrocarbon groups are bonded the nitrogen, they can be
the same or different groups.
The groups that came from the amine and are attached to the nitrogen are named
first with the same name as a side chain and end in yl. The rest of the molecule is named
in the same manner as the carboxylic acid except the ending is changed from oic acid to
amide. The common name for the amide uses the common name for the acid. In the
structures below, the standard name is listed first with the common name second.
Acid Chloride
Acid chlorides are formed by the reaction a carboxylic acid with thionyl chloride,
SOCl2. Acid chlorides can be used to make esters and amides.
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The compound is named in the same manner as the carboxylic acid except the ending is
changed from oic acid to oyl chloride. The common name for the acid chloride uses the
common name for the acid. In the structures below, the standard name is listed first with
the common name second.
Acid Anhydrides
Acid anhydrides are produced from carboxylic acids by a dehydration reaction.
They are usually formed from two molecules of the same acid. Acid anhydrides can be
used to make esters and amides.
The compound is named in the same manner as the carboxylic acid except the ending is
changed from oic acid to oic anhydride. The common name for the acid anhydride uses
the common name for the acid. In the structure below, the standard name is listed first
with the common name second.
The structures and names for some additional oxygen containing are shown below. See if
the names make sense using the rules discussed above.
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Structure
Standard Name (IUPAC)
1-butanol
Common Name
Butyl alcohol
2-butanol
(sec-butyl alcohol)
4-methyl-2-pentanol
Ethoxyethane
2-methoxybutane
Diethylether
(methyl sec-butyl ether)
Methanal
Formaldehyde
Ethanal
Acetaldehyde
4-methylhexanal
6-methyl-3-heptanone
4-chloropentanoic acid
Benzoic acid
Methyl propanoate
Methyl propionate
Methyl benzoate
Ethanamide
Acetamide
Dimethyl methanamide
Dimethyl formamide
Functional Groups Containing Nitrogen
Amines
Amines are derivatives of ammonia (NH3) formed by replacing the
hydrogen atoms with hydrocarbon groups. Amines are classified by how many
hydrocarbon groups are present: primary amine (RNH2), secondary amine (R2NH), or
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tertiary amine (R3N). The hydrocarbon groups can be the same or different. Choose the
longest continuous carbon chain that contains the NH2 group. Number the chain from the
end that will give the NH2 group the lowest number. This sets the direction and order of
the numbering in the whole molecule. The number of the NH2 group will be the number
of the carbon to which it is bonded. The side chains are numbered and named as with
alkanes. If the chain is short enough so that there is no doubt about the position of the
NH2 group, it is not given a number. The suffix for amines is amine. The prefix N- is
used for each substituent.
The common name uses the names of the side chains and the word amine. The
hydrocarbon groups are named as a side chain and end in yl. The groups are not
necessarily in alphabetical order. In the structures below, the standard name is given first
with the common name second.
Nitro Compounds
The nitro group, NO2, is named as a side chain and its position on the
hydrocarbon chain is numbered if necessary.
Nitriles
The nitrile group contains a carbon atom triply bonded to a nitrogen atom,
. Nitrile names are based on the number of carbon atoms present and the suffix
nitrile is added. Nitriles can be reacted with water to produce carboxylic acids. The
common name for nitriles is based on the common name of the carboxylic acid to which
it can be hydrolyzed. In the structure below, the standard name is listed first with the
common name second.
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The structures and names for some additional oxygen containing are shown below. See if
the names make sense using the rules discussed above.
Structure
Standard Name (IUPAC)
Methanamine
Common Name
Methylamine
2-propanamine
Isopropylamine
1,1-dimethylethanamine
t-butylamine
2,4,N,N-tetramethyl-3hexanamine
Propanenitrile
propionitrile
1,4-dinitrobenzene
p-dinitrobenzene
The material presented above should allow you to name many common organic
compounds or to derive a structure from its name.
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