Nomenclature

Nomenclature

IUPAC Naming Conventions

Naming Steps

• Primary goal of international union of pure and applied chemistry naming system is to create an unambiguous relationship between the name and structure of a compound.

1. Identify the Longest Carbon Chain Containing the Highest-Order Functional Group

• This will be called the parent chain, and will determine the roots of the name
• The highest priority functional group (with the most oxidized carbon) will provide the suffix
• If there are two or more carbon chains of equal length, then the more substituted chain gets priority as the parent chain.

2. Number the Chain

• The carbon numbered one will be the one closest to the highest-priority functional group.
• If the functional groups all have the same priority, numbering the chain should make the number of the substituted carbons as low as possible
  • The more oxidized a carbon is, the higher priority it has in the molecule.
    • Oxidation state increases with more bonds to heteroatoms (atoms beside hydrogen and carbon) and decreases with more bonds to hydrogen.
• For rings, numbers start at the point of greatest substitution, and continues in that direction
• If there is a tie between assigning priority in a molecule with double and triple bonds, the double bond takes precedence.

3. Name the Substituents

• Substituents are functional groups that are not part of the parent chain.
• Substituents name will be placed at the beginning of the compound name as a prefix, followed by the name of the longest chain.
• Only the highest priority functional group will determine the suffix for the compound
• Carbon chain substituents are named like alkanes, with suffix –yl replacing –ane
• n- prefix indicates that it is normal or is a straight chain alkane.
• If there are multiple substituents of the same type, prefixes such as di-, tri- & tetra- are used.

4. Assign a Number to Each Substituent

• Pair the substituents that you have named to the corresponding number in the parent chain
• Multiple substituents of the same type will get both the required prefix and a carbon number designation, even if they are on the same number

5. Complete the Name

• Always begins with the names of the substituents in alphabetical order, and each substituent is preceded by its number.
• Numbers are separated by commas, and word with hyphens
• Name is finished with the name of the parent chain with the suffix being the functional group of the highest priority.

Hydrocarbons and Alcohols

Alkanes

• Simple hydrocarbons with the formula:
• Goes methane, ethane, propane, butane, pentane, hexane, heptane, octane….
• Alkyl halides are alkanes with halogen substituents (common). Have the following prefixes: fluoro-, chloro- , bromo-, or iodo-.

Alkenes and Alkynes

• -ene indicates a double bond while –yne­ signifies a triple bond.
• Double bonds may be encountered in the context of unsaturated fatty acids
• Is indicated by the lower number carbon that precedes the bond: 2- butane or but-2-ene

Alcohols

• Are named by replacing –e in the name of the corresponding alkane with –ol.
• Chain is numbered so that the carbon attached to the hydroxyl group gets the lowest possible number. Hydroxyl group takes precedence over multiple bond since it increases the oxidation state of carbon the most.
• Hydroxyl substituent: alcohol is not the highest-priority functional group (hydroxyl-)
• Often referred to by their common names: the name of the alkyl group is followed by the word alcohol (e.g – 2-propanol is isopropyl alcohol & ethanol is ethyl alcohol)
• Alcohols with two hydroxyl groups are called dios or glycols and are indicated with the suffix –diol
  • Each hydroxyl group must be numbered
  • If hydroxyl group on same carbon, known as germinal diols. Also known as hydrates and are not commonly seen since they spontaneously dehydrate
  • Hydroxyl groups on adjacent carbons are called vicinal diols

Aldehydes and Ketones

• Contain a carbonyl group (carbon double bonded to oxygen)
• Aldehydes are chain terminating which means that the carbonyl group appears at the end of the parent chain.

Aldehydes

• Carbonyl group usually takes precedence over other groups and is therefore given the number.
• Named by replacing the –e of the parent alkane with the suffix –al.
• Methanal is formaldehyde; ethanol is acetaldehyde; propanal is propionaldehyde

Ketones

• Contain carboxyl group somewhere in the middle of the carbon chain.
• Named by replacing –e with –one
• List alkyl groups in alphabetical order and then end with ketone.
• Acetone is the smallest possible ketone molecule and it defies traditional naming conventions because it has three rather than two carbons.
• When carbonyl group is not highest priority, treat as substituents with prefix oxo-
  • Ketones can also be indicated by keto-
• Carbon adjacent to the carbonyl group is noted as alpha, and the successive carbons are referred to as beta, gamma, and delta carbons.

Carboxylic Acids and Derivatives

Carboxylic Acids

• Contain both carbonyl and hydroxyl group on a terminal carbon
• Since they are terminal functional groups, associated carbon is number 1.
• Most oxidized functional group that appears on MCAT, only carbon dioxide contains a more oxidized carbon. Thus are the highest priority functional groups.
• Named by replacing –e in the name of the parent alkane with the suffix –oic acid
• Formic Acid is the common name for methanoic acid, Acetic acid is ethanoic acid, and propionic acid is propanoic acid.

Esters

• Carboxylic acid derivatives in which hydroxyl group is replaced with an alkoxy group (-OR where R is a hydrocarbon chain)
• First term in the name is the alkyl name of the esterifying group (R group)
• Second term in the name is the name of the parent acid with -oate replacing the –oic acid

Amides

• Hydroxyl group is replaced by an amino group (nitrogen containing compound)
• Amino Nitrogen can be bonded to zero, one or two alkyl groups
• Named similar to esters except suffix becomes –amide.
• Substituents attached to nitrogen are labeled with N-
  • Included in prefix of compound name but are not numbered

Anhydrides

• The formation of an anhydride requires two carboxylic acid molecules with one water molecule being removed.
• Are mainly cyclic, and are named by replacing acid with anhydride if the anhydride is formed from only one type of carboxylic acid.
• If anhydride is not symmetrical (not the same two acids used), both carboxylic acids are named without the acid ending and anhydride is added to the end of the name.