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Naming Saturated Molecules with 2 Different Functional Groups Chemistry Tutorial

Key Concepts

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Seniority, Principal Group and Suffix

If a molecule contains 2 or more different functional groups we must determine which functional group is the most senior.
The table below places some common functional groups in order of decreasing seniority:

  Seniority of Functional Groups
  Class of
Compound 		Functional
Group 		Suffix
most senior carboxylic acids COOH oic acid
↓ esters -CO-O- oate
↓ amides -NH-CO- amide
↓ aldehydes -CO al
↓ ketones -CO- one
↓ alcohols -OH ol
least senior amines -NH2 amine

The most senior functional group in a molecule is called the "principal group" and it will determine the suffix given to the parent hydrocarbon (such as an alkane).

Consider the molecule shown below:

  H
|		   OH
|		   H
|		   O
||		  
H− C − C − C − C −OH
  |
H		   |
H		   |
H		      

It has 2 different functional groups:

The COOH functional group is more senior than the OH functional group.
The principal functional group is COOH and the suffix oic acid will end the name of the parent hydrocarbon.
So this molecule is named as an alkanoic acid

Consider the molecule shown below:

  H
|		   O
||		   H
|		   O
||		  
H− C − C − C − C −OH
  |
H		       |
H		      

It has 2 different functional groups:

The COOH functional group is more senior than the =O functional group.
The principal functional group is COOH and the suffix oic acid will end the name of the parent hydrocarbon.
So this molecule is named as an alkanoic acid

Consider the molecule shown below:

  H
|		   NH2
|		   H
|		   O
||		  
H− C − C − C − C −OH
  |
H		       |
H		      

It has 2 different functional groups:

The COOH functional group is more senior than the NH2 functional group.
The principal functional group is COOH and the suffix oic acid will end the name of the parent hydrocarbon.
So this molecule is named as an alkanoic acid

Consider the molecule shown below:

  H
|		   H
|		   O
||		   H
|		  
HO− C − C − C − C −H
  |
H		   |
H		       |
H		  

It has 2 different functional groups:

The =O functional group is more senior than the OH functional group.
The principal functional group is =O and the suffix one will end the name of the parent hydrocarbon because the =O is on a non-terminal carbon atom.
So this molecule is named as an alkanone

Consider the molecule shown below:

  H
|		   H
|		   H
|		   H
|		  
HO− C − C − C − C =O
  |
H		   |
H		          

It has 2 different functional groups:

The =O functional group is more senior than the OH functional group.
The principal functional group is =O and the suffix al will end the name of the parent hydrocarbon because the =O is on a terminal carbon atom.
So this molecule is named as an alkanal

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Naming and Numbering the Parent Hydrocarbon (Principal Chain)

Once we have determined which functional group is the most senior (the principal group) we need to:

The parent hydrocarbon for all the molecules below is butane because the longest carbon chain contains 4 carbon atoms.
Note that we number this carbon chain so that the most senior functional group (principal group) has the lowest number:

molecule parent
hydrocarbon 		principal
group 		suffix principal
chain
  H
|		   OH
|		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		   |
H		   |
H		      
butane COOH oic acid butanoic acid
  H
|		   O
||		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		       |
H		      
butane COOH oic acid butanoic acid
  H
|		   NH2
|		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		       |
H		      
butane COOH oic acid butanoic acid
  H
|		   H
|		   O
||		   H
|		  
HO− C(4) − C(3) − C(2) − C(1) −H
  |
H		   |
H		       |
H		  
butane =O
(on carbon 2)		 -2-one butan-2-one
  H
|		   H
|		   H
|		   H
|		  
HO− C(4) − C(3) − C(2) − C(1) =O
  |
H		   |
H		          
butane =O
(terminal)		 al butanal

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Adding Prefixes to the Principal Chain

The prefix given to the name of the principal chain will be determined by the name, and location, of the other functional group.
Some functional groups and their corresponding prefixes are given below:

Functional
Group 		Prefix
-CO- oxo
-OH hydroxy
-NH2 amino

The number representing the location of the less senior functional group on the chain is attached to the beginning of the prefix as a number followed by a hyphen.
The prefix is then attached to the name of the principal chain (no spaces between the prefix and the principal chain's name).

Using the same molecules as in the section above we can add a prefix to the name of the principal chain in order to name each molecule:

molecule principal chain locant
(less senior group) 		prefix
(less senior group) 		completed name
  H
|		   OH
|		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		   |
H		   |
H		      
butanoic acid 3 hydroxy 3-hydroxybutanoic acid
  H
|		   O
||		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		       |
H		      
butanoic acid 3 oxo 3-oxobutanoic acid
  H
|		   NH2
|		   H
|		   O
||		  
H− C(4) − C(3) − C(2) − C(1) −OH
  |
H		       |
H		      
butanoic acid 3 amino 3-aminobutanoic acid
  H
|		   H
|		   O
||		   H
|		  
HO− C(4) − C(3) − C(2) − C(1) −H
  |
H		   |
H		       |
H		  
butan-2-one 4 hydroxy 4-hydroxybutan-2-one
  H
|		   H
|		   H
|		   H
|		  
HO− C(4) − C(3) − C(2) − C(1) =O
  |
H		   |
H		          
butanal 4 hydroxy 4-hydroxybutanal

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Worked Examples of Naming Saturated Organic Compounds with 2 Different Functional Groups

Question 1: Lactic acid has the structural formula shown below:

  H
|		   HO
|		   O
||		  
H− C − C − C −OH
  |
H		   |
H		      

Apply the nomenclature rules to give a systematic IUPAC name for this molecule.

Solution:

  1. Identify all the functional groups

      H
    |    		   HO
    |    		   O
    ||    		   2 functional groups:

    (i) OH functional group

    (ii) COOH functional group

    H− C − C − C −OH
      |
    H    		   |
    H    		      

  2. Select the "principal group" and determine the suffix for the name of the parent hydrocarbon

    COOH functional group is more senior than the OH functional group.

    Principal group is COOH

    Suffix for name is oic acid

  3. Select the "principal chain" and name the parent hydrocarbon

      H
    |    		   HO
    |    		   O
    ||    		   Principal chain contains 3 carbon atoms (prop)

    Parent hydrocarbon is saturated (an alkane)

    Parent hydrocarbon is propane

    H− C − C − C −OH
      |
    H    		   |
    H    		      

  4. Number the chain giving principal group the lowest possible number

      H
    |    		   HO
    |    		   O
    ||    		   Principal group is COOH

    C of COOH is the first carbon (C(1))

    Chain is then numbered right to left

    H− C(3) − C(2) − C(1) −OH
      |
    H    		   |
    H    		      

  5. Name the "principal chain" : parent hydrocarbon + suffix

    Parent hydrocarbon is propane

    Suffix is oic acid (no number is required since "oic acid" implies this is a terminal functional group)

    Principal chain: "propane" + "oic acid", "e" of propane is removed when suffix is added to give the name propanoic acid

  6. Determine prefixes to be added to name of principal chain

      H
    |    		   HO
    |    		   O
    ||    		   OH is the less senior function group (named as hydroxy)

    OH attached to C(2) of the principal chain

    prefix: 2-hydroxy

    H− C(3) − C(2) − C(1) −OH
      |
    H    		   |
    H    		      

  7. Add prefixes in alphanumerical order to the principal chain's name

    prefix: 2-hydroxy

    principal chain: propanoic acid

    systematic name: 2-hydroxypropanoic acid

Question 2: The structural formula of an organic molecule is shown below:

      H
|		              
  H
|		 H-
 		 C
|		 -H
 		 H
|		   O
||		   H
|		  
OH− C − C − C − C − C −H
  |
H		   |
H		   |
H		       |
H		  

Apply the nomenclature rules to give a systematic IUPAC name for this molecule.

Solution:

  1. Identify all the functional groups

          H
    |    		               2 functional groups:

    (i) OH functional group

    (ii) =O functional group

      H
    |    		 H-
         		 C
    |    		 -H
         		 H
    |    		   O
    ||    		   H
    |    		  
    OH− C − C − C − C − C −H
      |
    H    		   |
    H    		   |
    H    		       |
    H    		  

  2. Select the "principal group" and determine the suffix for the name of the parent hydrocarbon

    =O is more senior than OH

    Principal group is =O

    =O bonded to a non-terminal carbon atom results in the "one" suffix which will require a locant

  3. Select the "principal chain" and name the parent hydrocarbon

    Principal chain will include both functional groups

          H
    |    		               Principal chain contains 5 carbon atoms (pent)

    Parent hydrocarbon is saturated (an alkane)

    Parent hydrocarbon is pentane

      H
    |    		 H-
         		 C
    |    		 -H
         		 H
    |    		   O
    ||    		   H
    |    		  
    OH− C − C − C − C − C −H
      |
    H    		   |
    H    		   |
    H    		       |
    H    		  

  4. Number the chain giving principal group the lowest possible number

          H
    |    		               Principal group is =O

    Chain is numbered from right to left

    =O is attached to C(2)

    Suffix will be -2-one

      H
    |    		 H-
         		 C
    |    		 -H
         		 H
    |    		   O
    ||    		   H
    |    		  
    OH− C(5) − C(4) − C(3) − C(2) − C(1) −H
      |
    H    		   |
    H    		   |
    H    		       |
    H    		  

  5. Name the "principal chain" : parent hydrocarbon + suffix

    parent hydrocarbon is pentane

    suffix is -2-one

    Principal chain : "pentane" + "-2-one", "e" of pentane removed when suffix is added to give pentan-2-one

  6. Determine prefixes to be added to name of principal chain

          H
    |    		               Less senior functional group is OH (hydroxy)

    OH on C(5) gives prefix 5-hydroxy

    CH3 branch off principal chain (methyl)

    CH3 on C(4) gives prefix 4-methyl

      H
    |    		 H-
         		 C
    |    		 -H
         		 H
    |    		   O
    ||    		   H
    |    		  
    OH− C(5) − C(4) − C(3) − C(2) − C(1) −H
      |
    H    		   |
    H    		   |
    H    		       |
    H    		  

  7. Add prefixes in alphanumerical order to the principal chain's name

    Arrange prefixes alphabetically: h (hydroxy) before m (methyl)

    Prefix will be 5-hydroxy-4-methyl

    Attach prefixes to name of principal chain (pentan-2-one)

    5-hydroxy-4-methylpentan-2-one

Footnotes:

(1) A saturated organic molecule contains only single bonds between carbon atoms.
An unsaturated organic molecule contains 1 or more double and/or triple bonds between carbon atoms.

(2) An organic molecule may contain many different functional groups ofcourse, but our discussion will be limited to just 2.

(3) IUPAC is the abbreviation for the International Union of Pure and Applied Chemistry.

(4) There are a number of different systems for naming organic molecules.
We will be using a substitutive system which is commonly used to name most organic compounds with the notable exceptions of esters and anhydrides which are named using functional class nomenclature.

(5) Note that the name we use to refer to a functional group is different to the prefix and suffix we use when naming an organic molecule:

COOH is the carboxyl functional group, the suffix used is oic acid

OH is the hydroxyl functional group, prefix used is hydroxy, suffix used is ol

C=O is the carbonyl functional group, prefix used is oxo, suffix used is either one (non-terminal C atom) or al (terminal C atom)

(6) The rules for naming organic compounds are still being developed by IUPAC.
The most recent document for referral is "Preferred names in the nomenclature of organic compounds" (Draft 7 October 2004).
The current document recognises that there is more than one way to systematically name organic compounds, and develops rules for assigning "preferred IUPAC names", but any other name, as long as it is unambiguous and follows the principles of the IUPAC recommendations is acceptable as a "general IUPAC name".
As a result, there are examples of "preferred IUPAC" names that are based on the tradition of use, rather than a system of naming. Examples of these traditional names that students may be expected to know are acetone, acetic acid and its derivatives such as ethyl acetate and acetic anhydride, formic acid and its derivatives such as ethyl formate.

(7) Technically, a "straight chain carbon compound" is an acyclic aliphatic organic compound.
Acyclic, or non-cyclic, means that the carbon atoms form a chain and joined up in a ring.
Aliphatic comes from the Greek aleiphatos meaning "fat". Early Chemists did not know the structure of a fat, but they did know that compounds containing long hydrocarbon chains behaved in a similar way to fats. So compounds containing hydrocarbon chains came to be known as aliphatic compounds.
Organic compounds are, in general, compounds that contain carbon.

(8) Or, as many of the functional groups as possible if you are dealing with more than 2 functional groups.
Note that the "principal chain" may be unsaturated, that is, it may contain double bonds and/or triple bonds between the carbon atoms.