Naming Organic Molecules


What's in a name?
Would a rose smell as sweet
if you couldn't correctly name
the aldehydic components
of its scent?

Alkanes


  1. Name the longest carbon chain (root + "ane")
  2. Name the branches (root + "yl")
  3. Number the long chain
  4. List the substituents alphabetically




Examples:





Cycloalkanes

  1. Use the prefix "cyclo" to indicate a cycloalkane.

  2. Indicate the position of substituents on the ring with numbers. Count around the ring so as to give the substituents the lowest numbers possible.

  3. Substituents on the same side of the ring are cis. Those on opposite sides are trans.

  4. Name the fragment as a cycloalkyl group when it is a substituent on a longer alkyl chain.

  5. Label polycyclic molecules with the prefixes: bicyclo, tricyclo, tetracyclo, etc. depending on the number of bonds that must be broken to form a monocyclic structure.

  6. For bicyclic compounds, count the total number of carbons in the rings for the parent bicycloalkane. Put the number of carbons between each bridge carbon in square brackets, separated by periods.


Examples:





Alkyl Halides


  • These are named as alkane derivatives
  • Number the longest chain so as to give the substituents the lowest number possible
  • Use chloro, bromo, or iodo for the halide substitutents




Stereoisomers


  • Chiral compounds can be names according to the direction they rotate plane polarized light:

      (+)-2-iodobutane


      (-)-2-iodobutane

  • Chiral compounds can be named according to absolute stereochemistry:

      (R)-1-bromo-1-chloroethane


      (S)-1-bromo-1-chloroethane

  • When there is more than 1 asymmetric center, the number of the asymmetric carbon and its absolute configuration are put in parentheses.





Alkenes


  1. Find longest chain containing the double bond, name this as the alkene. Give the double bond the lowest number possible.

  2. List substituents with prefixes.

  3. Give stereochemistry about the double bond with cis, trans prefixes for disubstituted olefins; E, Z prefixes for tri- and tetrasubstituted olefins.

      cis - The 2 substituents are on the same side of the double bond or ring.

      trans - The 2-substituents are on opposite sides of the double bond or ring.

      Z (zusammen, together) - The 2 highest priority substitutents are on the same side of a double bond.

      E (entgegen, opposite) - The 2 highest priority substitutents are on opposite sides of a double bond.

  4. Cyclic olefins are named as cycloalkenes, with the carbons of the double bond being C1 and C2.

  5. Unsaturated substituents are named as alkenyl groups. Numbering starts at the connection to the main chain.

  6. The hydroxy group has priority over the double bond. Molecules with both are named as alkenols.


Examples:





Alkynes


  1. Alkynes are names as derivativatives of alkanes with the suffix "yne" replacing "ane".

  2. The position of the triple bond is indicated by a number. Count along the longest chain containing the triple bond so as to make this number as small as possible.

  3. If the molecule has both a triple bond and a hydroxyl group, name it as an alkynol. Give the OH substitutent the lowest number possible.

  4. If the molecule has both a double bond and a triple bond, name it as an alkenyne. Give the double bond the lowest number possible.

  5. When there is a triple bond in a substituent, name the substituent as an alkynyl group.

Examples:





Alcohols and Thiols


  1. Alcohols are named as alkanols.
      Find the longest chain containing the OH.


  2. Thiols are named as alkanethiols.
      Find the longest chain containing the SH.




  3. Cyclic molcules with an OH or SH substitutent are named as cycloalkanols or cycloalkanethiols.
      The carbon bearing the OH (SH) group is numbered as C1.


  4. As a substituent:
    • OH is a "hydroxy" group.
    • SH is a "mercapto" group.


  5. A molecule with 2 hydroxy groups is a diol, with 3 is a triol, etc.

  6. Benzenols are frequently named as phenols.


Ethers and Sulfides








Phenols and Aryl Ethers


A hydroxybenzene is called a phenol. Derivatives of benzene that contain an OH group on the ring are usually named as derivatives of phenol. IUPAC nomenclature for a phenol is benzenol.

Carbonyl Compounds

  1. Aldehydes
    • Take the name of the alkane and replace the e by al.

    • An aldehyde derivative of a cycloalkane is named as a carboxaldehyde.

    • When the CHO group is named as a substitutent, it is methanoyl or formyl.




  2. Ketones
    • Ketones are named as alkanones. Take the name of the alkane and replace the e by one. Assign the lowest possible number in the alkyl chain to the carbonyl carbon.

    • In complicated cycloalkanes, the ketone group is indicated by oxo.

    • When the ketone is part of a substituent, it is an alkanoyl group. The unit CH3CO is commonly referred to as acetyl.




  3. Carboxylic acids
    • Carboxylic acids are named as alkanoic acids. Take the name of the alkane (longest chain containing the CO2H) and replace the e by oic acid.

    • If the chain contains a double bond, name the compound as an alkenoic acid.

    • Molecules with 2 CO2H groups are named as alkanedioic acids.

    • For cyclic molecules containing the CO2H group, name it as a cycloalkanecarboxylic acid.

    • Acid anhydrides are named as alkanoic alkanoic anhydrides, or simply as alkanoic anhydrides when both acyl groups are the same.
        These are derivatives of 2 carboxylic acid.

        Take the first (alphabetically) carboxylic acid and replace the oic acid by oic . Do the same with the second. Add anhydride tot hte end.


  4. Carboxylic acid esters
      These are derivatives of carboxylic acids and named as alkyl alkanoates.

        First name the alkyl group attached to the ester oxygen.

        Second, replace the oic acid of the parent carboxylic acid with oate.


  5. Carboxylic acid amides
    • These are derivatives of carboxylic acids and named by replacing the oic acid with amide.

    • Alkyl groups bonded to the nitrogen of the amide are indicated by N-alkyl or N,N-dialkyl.


  6. Carboxylic acid halides
      These are derivatives of carboxylic acids and named by replacing the oic acid with oyl halide.


Nitriles


These are derivatives of carboxylic acids and named by replacing the oic acid with enitrile.

They are sometimes names as alkyl cyanides.

When it is a substituent, it is a cyano group.



Amines

Amines can be named as alkylamines or alkaneamines.

  • When named as an alkylamine, the nitrogen is considered to be bonded to C1 of the chain.
      Example:
      CH3CH(NH2)CH2CH2CH3
      1-methylbutylamine

  • When named as an alkaneamine:
      Find the longest alkyl chain bearing the nitrogen.
      Number the chain so as to give the amine the smallest number possible.

      Example:
      CH3CH(NH2)CH2CH2CH3
      2-pentaneamine
The degree of substitution at nitrogen determines the primary, secondary, tertiary designation for an amine.

Phenylamine is also called aniline. Derivatives can be named as aniline derivatives or arylamine derivatives. Additional alkyl groups on the nitrogen atom are indicated by the prefix "N" follwed by the alkyl.






Professor Patricia Shapley, University of Illinois, 2012