Short Summary of IUPAC Nomenclature of Organic Compounds

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Short Summary of IUPAC Nomenclature of Organic Compounds...

    Short Summary of IUPAC Nomenclature of Organic Compounds


    The purpose of the IUPAC system of nomenclature is to establish an international standard of naming compounds to facilitate communication. The goal of the system is to give each structure a unique and unambiguous name, and to correlate each name with a unique and unambiguous structure.

I. Fundamental Principle

    IUPAC nomenclature is based on naming a molecule’s longest chain of carbons connected by

    single bonds, whether in a continuous chain or in a ring. All deviations, either multiple bonds or atoms other than carbon and hydrogen, are indicated by prefixes or suffixes according to a specific set of priorities.

II. Alkanes and Cycloalkanes

    Alkanes are the family of saturated hydrocarbons, that is, molecules containing carbon and hydrogen connected by single bonds only. These molecules can be in continuous chains (called linear or acyclic), or in rings (called cyclic or alicyclic). The names of alkanes and cycloalkanes are the root names of organic compounds. Beginning with the five-carbon alkane, the number of carbons in the chain is indicated by the Greek or Latin prefix. Rings are designated by the prefix “cyclo”. (In the geometrical symbols for rings, each apex represents a carbon with the number of

    hydrogens required to fill its valence.)

     methane dodecane CH4 CH3[CH2]10CH3 ethane tridecane CH3CH3 CH3[CH2]11CH3 propane tetradecane CH3CH2CH3 CH3[CH2]12CH3 butane icosane CH3[CH2]2CH3 CH3[CH2]18CH3 pentane henicosane CH3[CH2]3CH3 CH3[CH2]19CH3 hexane docosane CH3[CH2]4CH3 CH3[CH2]20CH3 heptane tricosane CH3[CH2]5CH3 CH3[CH2]21CH3 octane triacontane CH3[CH2]6CH3 CH3[CH2]28CH3 nonane hentriacontane CH3[CH2]7CH3 CH3[CH2]29CH3 decane tetracontane CH3[CH2]8CH3 CH3[CH2]38CH3 undecane pentacontane CH3[CH2]9CH3 CH3[CH2]48CH3

    H H


     H H C C

    cyclopropane cyclobutane cyclopentane H H

    cyclohexane cycloheptane cyclooctane

    Short Summary of IUPAC Nomenclature, p. 2

    III. Nomenclature of Molecules Containing Substituents and Functional Groups

A. Priorities of Substituents and Functional Groups

    LISTED HERE FROM HIGHEST TO LOWEST PRIORITY, except that the substituents within

    Group C have equivalent priority.

    Group AFunctional Groups Indicated By Prefix Or Suffix

    Family of Compound Structure Prefix Suffix


    Carboxylic Acid R C OH carboxy- -oic acid

    (-carboxylic acid) O

    Aldehyde R C H oxo- -al

     (formyl) (carbaldehyde) O C R Ketone R oxo- -one

    R O H Alcohol hydroxy- -ol

    R N Amine amino- -amine

    Group BFunctional Groups Indicated By Suffix Only

    Family of Compound Structure Prefix Suffix

    C C Alkene -------- -ene

    C C Alkyne -------- -yne

    Group CSubstituents Indicated by Prefix Only

    Substituent Structure Prefix Suffix

    R Alkyl (see list below) alkyl- ----------

    R O Alkoxy alkoxy- ----------

    F Halogen fluoro- ----------

    Cl chloro- ----------

    Br bromo- ----------

    I iodo- ----------

    Group C continued on next page

Short Summary of IUPAC Nomenclature, p. 3

    Group CSubstituents, continued

Miscellaneous substituents and their prefixes

    CH NO2 CH2 CH2CH CH2

    nitro vinyl allyl


Common alkyl groups—replace “ane” ending of alkane name with “yl”. Alternate names for

    complex substituents are given in brackets.

    CH3 3 3 CHCH

    methyl CH CH

     CH3 CH2CH3 isopropyl sec-butyl CH2CH3 [1-methylethyl] [1-methylpropyl] ethyl

     CH3 CH3

    CH2 CH CH2CH2CH3 C CH3 propyl (n-propyl) CH3 CH3 isobutyl tert-butyl or t-butyl [2-methylpropyl] [1,1-dimethylethyl] CH2CH2CH2CH3

    butyl (n-butyl)

B. Naming Substituted Alkanes and CycloalkanesGroup C Substituents Only

    1. Organic compounds containing substituents from Group C are named following this sequence of steps, as indicated on the examples below:

    ?Step 1. Find the longest continuous carbon chain. Determine the root name for this parent chain. In cyclic compounds, the ring is usually considered the parent chain, unless it is attached to a longer chain of carbons; indicate a ring with the prefix “cyclo” before the root

    name. (When there are two longest chains of equal length, use the chain with the greater number of substituents.)

    ?Step 2. Number the chain in the direction such that the position number of the first substituent is the smaller number. If the first substituents from either end have the same number, then number so that the second substituent has the smaller number, etc.

    ?Step 3. Determine the name and position number of each substituent. (A substituent on a nitrogen is designated with an “N” instead of a number; see Section III.D.1. below.)

    ?Step 4. Indicate the number of identical groups by the prefixes di, tri, tetra, etc.

    ?Step 5. Place the position numbers and names of the substituent groups, in alphabetical order, before the root name. In alphabetizing, ignore prefixes like sec-, tert-, di, tri, etc., but

    include iso and cyclo. Always include a position number for each substituent, regardless of redundancies.

Short Summary of IUPAC Nomenclature, p. 4


    6 7 8 5 6 7

     CH3 CH2CH2CH3 CH2CH2CH3 1 2 3 1

     CH CH CH C CH CH CH3 CH3 CH2CH3 CH CHCH3 24 5 3 4

     Cl Br CH3 CH3 F CH3

    3-bromo-2-chloro-5-ethyl-4,4-dimethyloctane 3-fluoro-4-isopropyl-2-methylheptane

    H3C CHCH2CH3

    1 1-sec-butyl-3-nitrocyclohexane 2 6 (numbering determined by the

    alphabetical order of substituents) 5 3 NO2 4

C. Naming Molecules Containing Functional Groups from Group BSuffix Only

    1. AlkenesFollow the same steps as for alkanes, except:

    a. Number the chain of carbons that includes the C=C so that the C =C has the lower

    position number, since it has a higher priority than any substituents;

    b. Change “ane” to “ene” and assign a position number to the first carbon of the C =C;

    c. Designate geometrical isomers with a cis,trans or E,Z prefix.

    CH3 F F


     CH CH CH C C CH CH2 CH2 1 4

    F F CH3 CH3

    2 3 4,4-difluoro-3-methylbut-1-ene 1,1-difluoro-2-methyl-

    5-methylcyclopenta- buta-1,3-diene


    Special case: When the chain cannot include the C=C, a substituent name is used.

    CH 3-vinylcyclohex-1-ene CH2

     AlkynesFollow the same steps as for alkanes, except: 2.

    a. Number the chain of carbons that includes the CtC so that the functional group has the

    lower position number;

    b. Change “ane” to “yne” and assign a position number to the first carbon of the CtC.

Note: The Group B functional groups (alkene and alkyne) are considered to have equal priority:

    in a molecule with both a double and a triple bond, whichever is closer to the end of the chain

    determines the direction of numbering. In the case where each would have the same position

    number, the double bond takes the lower number. In the name, “ene” comes before “yne”

    because of alphabetization. See examples on next page.

Short Summary of IUPAC Nomenclature, p. 5

    H F 1 2 3 4 5 5 4 3 2 1


    pent-3-en-1-yne pent-1-en-4-yne F CH3 ("yne" closer to end ("ene" and "yne" have equal 4,4-difluoro-3-methylbut-1-yne of chain) priority unless they have the

    same position number, when

    "ene" takes the lower number)

(Notes: 1. An “e” is dropped if the letter following it is a vowel: “pent-3-en-1-yne” , not “3-

    pent-3-ene-1-yne”. 2. An “a” is added if inclusion of di, tri, etc., would put two consonants

    consecutively: “buta-1,3-diene”, not “but-1,3-diene”.)

D. Naming Molecules Containing Functional Groups from Group APrefix or Suffix

    In naming molecules containing one or more of the functional groups in Group A, the group of highest priority is indicated by suffix; the others are indicated by prefix, with priority equivalent to any other substituents. The table in Section III.A. defines the priorities; they are discussed

    below in order of increasing priority.

    Now that the functional groups and substituents from Groups A, B, and C have been described, a modified set of steps for naming organic compounds can be applied to all simple structures:

    ?Step 1. Find the highest priority functional group. Determine and name the longest continuous carbon chain that includes this group.

    ?Step 2. Number the chain so that the highest priority functional group is assigned the lower number.

    ?Step 3. If the carbon chain includes multiple bonds (Group B), replace “ane” with “ene”

    for an alkene or “yne” for an alkyne. Designate the position of the multiple bond with the

    number of the first carbon of the multiple bond.

    ?Step 4. If the molecule includes Group A functional groups, replace the last “e” with the

    suffix of the highest priority functional group, and include its position number.

    ?Step 5. Indicate all Group C substituents, and Group A functional groups of lower priority, with a prefix. Place the prefixes, with appropriate position numbers, in alphabetical order before the root name.

1. Amines: prefix: amino-; suffix: -amine—substituents on nitrogen denoted by “N

     CH3O NH2 CH3CH2 CH2CH3



    propan-1-amine 3-methoxycyclohexan-1-amine N,N-diethylbut-3-en-2-amine

    ("1" is optional in this case)

    Short Summary of IUPAC Nomenclature, p. 6

    2. Alcohols: prefix: hydroxy-; suffix: -ol




    ethanol but-3-en-2-ol NH2


    ("1" is optional in this case) 3. Ketones: prefix: oxo-; suffix: -one

    CH3 O H3C

    O O N

    CH C C CH3 CH3 CH3 CH2 C CH2

     4-(N,N-dimethylamino)pent-4-en-2-one OH

    3-hydroxybutan-2-one cyclohex-3-en-1-one

    ("1" is optional in this case)

4. Aldehydes: prefix: oxo-, or formyl- (O=CH-); suffix: -al (abbreviation: CHO).

    An aldehyde can only be on carbon 1, so the “1” is generally omitted from the name.

    O O OH O O O


    methanal; ethanal; 4-hydroxybut-2-enal 4-oxopentanal

    formaldehyde acetaldehyde

    Special case: When the chain cannot include the carbon of the CHO, the suffix “carbaldehyde” is used:


    CH cyclohexanecarbaldehyde

5. Carboxylic Acids: prefix: carboxy-; suffix: -oic acid (abbreviation: COOH).

    A carboxylic acid can only be on carbon 1, so the “1” is generally omitted from the name.

    O O O O O CH3


     ethanoic acid; methanoic acid;

    acetic acid NH2 CH3 formic acid

    2-amino-3-phenylpropanoic acid 2,2-dimethyl-3,4-

    dioxobutanoic acid

(Note: Chemists traditionally use, and IUPAC accepts, the names “formic acid” and “acetic

    acid” in place of “methanoic acid” and “ethanoic acid”.)

Special case: When the chain numbering cannot include the carbon of the COOH, the suffix

    “carboxylic acid” is used. See example on next page.

Short Summary of IUPAC Nomenclature, p. 7


    2 2-formyl-4-oxocyclohexanecarboxylic acid 3

     ("formyl" is used to indicate an aldehyde as 1 a substituent when its carbon cannot be in O COOH 4 the chain numbering)

E. Naming Carboxylic Acid Derivatives

    The six common groups derived from carboxylic acids are salts, anhydrides, esters, acyl halides,

    amides, and nitriles. Salts and esters are most important.

1. Salts of Carboxylic Acids

    Salts are named with cation first, followed by the anion name of the carboxylic acid, where “ic

    acid” is replaced by “ate” :

    acetic acid acetate becomes

    butanoic acid becomes butanoate

    cyclohexanecarboxylic acid becomes cyclohexanecarboxylate

2. Esters

    Esters are named as “organic salts” that is, the alkyl name comes first, followed by the name of the carboxylate anion. (common abbreviation: COOR)

    carboxylate alkyl

    O O CH3 O CH3


     "alkanoate" "alkyl" ethyl acetate

    CH3 "alkyl alkanoate" isopropyl 2,2-dimethylpropanoate



    vinyl prop-2-enoate

    cyclohexyl 2-phenylacetate C HO OCH3

    methyl 3-hydroxycyclopentanecarboxylate

IV. Nomenclature of Aromatic Compounds

    “Aromatic” compounds are those derived from benzene and similar ring systems. As with aliphatic nomenclature described above, the process is: determining the root name of the parent

    ring; determining priority, name, and position number of substituents; and assembling the name

    in alphabetical order. Functional group priorities are the same in aliphatic and aromatic


    Short Summary of IUPAC Nomenclature, p. 8

A. Common Parent Ring Systems

    88 1 9 1 7 7 2 2


     6 3 6 3 5 4 5 10 4 benzene naphthalene anthracene

B. Monosubstituted Benzenes

    1. Most substituents keep their designation, followed by the word “benzene”:

    Cl NO2 2CH3 CH

    chlorobenzene nitrobenzene ethylbenzene

2. Some common substituents change the root name of the ring. IUPAC accepts these as root

    names, listed here in decreasing priority:


    benzoic benzene- benzaldehyde phenol aniline anisole toluene

    acid sulfonic acid

C. Disubstituted Benzenes

    1. Designation of substitutiononly three possibilities:

    X X X




    common: ortho- meta- para-

    IUPAC: 1,2- 1,3- 1,4-

2. Naming disubstituted benzenesPriorities determine root name and substituents

     Br COOH


    NH2 OCH3

    Br CHO CH3 3-aminobenzoic acid

    1,4-dibromobenzene 2-methoxybenzaldehyde 3-methylphenol

Short Summary of IUPAC Nomenclature, p. 9

D. Polysubstituted Benzenes


    Cl O2N NO2

     HN Cl OH

    CH3 NO2 NH2

    3,4-dichloro-N-methylaniline 2,4,6-trinitrotoluene ethyl 4-amino-3-hydroxybenzoate


    E. Aromatic Ketones

    A special group of aromatic compounds are ketones where the carbonyl is attached to at least one

    benzene ring. Such compounds are named as “phenones”, the prefix depending on the size and

    nature of the group on the other side of the carbonyl. These are the common examples:

    O O

    C CH3 2CH3 C CH

    acetophenone propiophenone

    O O

    C C CH2CH2CH3

    butyrophenone benzophenone

    Courtesy of Dr. Jan Simek, California Polytechnic State University at San Luis Obispo

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