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Short Summary of IUPAC Nomenclature of Organic Compounds
Introduction 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.)
CH 4 methane CH 3 [CH 2 ] 10 CH 3 dodecane CH 3 CH 3 ethane CH 3 [CH 2 ] 11 CH 3 tridecane CH 3 CH 2 CH 3 propane CH 3 [CH 2 ] 12 CH 3 tetradecane CH 3 [CH 2 ] 2 CH 3 butane CH 3 [CH 2 ] 18 CH 3 icosane CH 3 [CH 2 ] 3 CH 3 pentane CH 3 [CH 2 ] 19 CH 3 henicosane CH 3 [CH 2 ] 4 CH 3 hexane CH 3 [CH 2 ] 20 CH 3 docosane CH 3 [CH 2 ] 5 CH 3 heptane CH 3 [CH 2 ] 21 CH 3 tricosane CH 3 [CH 2 ] 6 CH 3 octane CH 3 [CH 2 ] 28 CH 3 triacontane CH 3 [CH 2 ] 7 CH 3 nonane CH 3 [CH 2 ] 29 CH 3 hentriacontane CH 3 [CH 2 ] 8 CH 3 decane CH 3 [CH 2 ] 38 CH 3 tetracontane CH 3 [CH 2 ] 9 CH 3 undecane CH 3 [CH 2 ] 48 CH 3 pentacontane
cyclohexane cycloheptane cyclooctane
cyclopropane cyclobutane cyclopentane
C
C
C
H H
H
H H
H
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.
Family of Compound
Alkene
Alkyne
Structure Prefix
Suffix
-ene
-yne
Suffix
-oic acid (-carboxylic acid)
-al (carbaldehyde)
-one
-ol
-amine
Prefix
carboxy-
oxo- (formyl)
oxo-
hydroxy-
amino-
Family of Compound Structure
Carboxylic Acid
Aldehyde
Ketone
Alcohol
Amine
R C
O
OH
C H
O
R
R C
O
R
O H
N
R
R
C C
C C
Group A—Functional Groups Indicated By Prefix Or Suffix
Group B—Functional Groups Indicated By Suffix Only
Group C—Substituents Indicated by Prefix Only
Substituent Structure Prefix Suffix
Alkyl (see list below) R — alkyl- ----------
Alkoxy R — O — alkoxy- ----------
Halogen F — fluoro- ---------- Cl — chloro- ---------- Br — bromo- ---------- I — iodo- ----------
Group C continued on next page
Examples
1- sec -butyl-3-nitrocyclohexane (numbering determined by the alphabetical order of substituents)
3-bromo-2-chloro-5-ethyl-4,4-dimethyloctane 3-fluoro-4-isopropyl-2-methylheptane
6 7 6
4
5
4 5
1
3
3
2
2
1
8 7
6
5 4
1 2 3
H 3 C CHCH 2 CH 3
NO 2
CH CH CHCH 3
CH 2 CH 2 CH 3
CH 3
CH 3 CH CH C
Br CH 3
CH
CH 2 CH 2 CH 3
CH
CH 3
CH 3
Cl
CH 2 CH 3
CH 3
F
C. Naming Molecules Containing Functional Groups from Group B—Suffix Only
- Alkenes—Follow 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.
1
2 3
4
5
4,4-difluoro-3-methylbut-1-ene 1,1-difluoro-2-methyl- buta-1,3-diene 5-methylcyclopenta- 1,3-diene
CH CH CH CH 2
F
F CH 3
C
CH 3
C
F
F
CH CH 2
CH 3
Special case: When the chain cannot include the C=C, a substituent name is used.
CH CH 2 3-vinylcyclohex-1-ene
- Alkynes—Follow the same steps as for alkanes, except:
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.
4,4-difluoro-3-methylbut-1-yne
pent-3-en-1-yne pent-1-en-4-yne ("ene" and "yne" have equal priority unless they have the same position number, when "ene" takes the lower number)
CH
CH 3
CH
F
F
C CH HC C C CHCH 3 HC C CH 2 CH CH 2
H
1 2 3 4 5 5 4 3 2 1
("yne" closer to end of chain)
(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 A—Prefix 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.
- Amines: prefix: amino-; suffix: -amine—substituents on nitrogen denoted by “ N ”
3-methoxycyclohexan-1-amine N , N -diethylbut-3-en-2-amine ("1" is optional in this case)
propan-1-amine
CH 3 CH 2 CH 2 NH 2
CH 3 O NH 2
CH 2 CH CHCH 3
N
CH 3 CH 2 CH 2 CH 3
2-formyl-4-oxocyclohexanecarboxylic acid ("formyl" is used to indicate an aldehyde as a substituent when its carbon cannot be in the chain numbering)
COOH
CHO
O
1
3 2
4
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.
- 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 ” :
acet ic acid becomes acet ate butano ic acid becomes butano ate cyclohexanecarboxyl ic acid becomes cyclohexanecarboxyl ate
- 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)
isopropyl 2,2-dimethylpropanoate
ethyl acetate "alkyl alkanoate"
"alkanoate" "alkyl"
carboxylate alkyl
C O
O
R R H 3 C C
O
O CH 2 CH 3 H 3 C C
CH 3
CH 3
C
O
O CHCH 3
CH 3
methyl 3-hydroxycyclopentanecarboxylate
cyclohexyl 2-phenylacetate
vinyl prop-2-enoate
CH 2 CH C
O
O CH CH 2
HO C
O
OCH 3
CH 2 COO
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 nomenclature.
A. Common Parent Ring Systems
naphthalene anthracene
benzene
8 7
6 5 4
3
2 2
1
10
8 9 7
6 4 5
3
1
or
B. Monosubstituted Benzenes
- Most substituents keep their designation, followed by the word “benzene”:
chlorobenzene nitrobenzene ethylbenzene
Cl NO 2 CH 2 CH 3
- Some common substituents change the root name of the ring. IUPAC accepts these as root names, listed here in decreasing priority:
benzene- benzaldehyde phenol aniline anisole toluene sulfonic acid
benzoic acid
COOH SO 3 H CHO OH NH 2 OCH 3 CH 3
C. Disubstituted Benzenes
- Designation of substitution—only three possibilities:
para- 1,4-
meta- 1,3-
ortho- 1,2-
common: IUPAC:
X X X
Y
Y
Y
- Naming disubstituted benzenes—Priorities determine root name and substituents
2-methoxybenzaldehyde 3-methylphenol
3-aminobenzoic acid 1,4-dibromobenzene
Br
Br
NH 2
COOH
OCH 3
CHO CH 3
HO
