IUPAC Nomenclature of Organic Compounds

IUPAC Nomenclature Overview

  • IUPAC nomenclature is a systematic approach to naming organic and inorganic compounds governed by the International Union of Pure and Applied Chemistry (IUPAC).

  • The system is particularly essential for understanding the structure and classification of compounds based on their functional groups and chain structure.

Required Material for IB DP Chemistry

  • Emphasis on IUPAC nomenclature as per the IB Diploma Programme Chemistry Guide, focusing on:

    • Saturated compounds

    • Mono-unsaturated compounds (containing one double or one triple bond)

    • Compounds with carbon chains up to six carbon atoms

    • Functional groups to be considered:

    • Halogeno

    • Hydroxyl

    • Carbonyl (both aldehydes and ketones)

    • Carboxyl (carboxylic acids and esters)

  • Inclusion of both straight-chain and branched-chain isomers.

Organic Name Prefixes Based on the Number of Carbon Atoms

  • A table of prefixes correlating the number of carbon atoms in the parent chain:

    • 1 Carbon: Meth

    • 2 Carbons: Eth

    • 3 Carbons: Prop

    • 4 Carbons: But

    • 5 Carbons: Pent

    • 6 Carbons: Hex

    • 7 Carbons: Hept

    • 8 Carbons: Oct

    • 9 Carbons: Non

    • 10 Carbons: Dec

Identical Substituents in the Same Chain

  • Numerical prefixes used for identical substituents:

    • 1 identical substituent: Mono

    • 2 identical substituents: Di

    • 3 identical substituents: Tri

    • 4 identical substituents: Tetra

    • 5 identical substituents: Penta

    • 6 identical substituents: Hexa

Functional Groups and Their Suffixes

Common Functional Groups

  • A detailed table of functional groups, their IUPAC names, suffixes, and examples:

Class

Functional Group

Name of Functional Group

Suffix in IUPAC Name

Example of Compound

General Formula

Alkane

-

-

-ane

C₂H₆ (Ethane)

Cₕ₂n+₂

Alkene

-C=C

Alkenyl

-ene

H₂C=CH₂ (Ethene)

CₙH₂n

Alkyne

-C≡C

Alkynyl

-yne

HC≡CH (Ethyne)

CₙH₂n-2

Alcohol

-OH

Hydroxyl

-anol

C₂H₅OH (Ethanol)

CₙH₂n₊₁OH

Ether

R-O-R'

Alkoxy

-oxyalkane

H₃C-O-C₂H₅ (Methoxyethane)

CₙH₂n+₂O

Aldehyde

-CHO

Carbonyl

-anal

C₃H₆O (Propanal)

R-CHO

Ketone

R-CO-R'

Carbonyl

-anone

C₃H₆O (Propanone)

R-CO-R'

Carboxylic Acid

-COOH

Carboxyl

-anoic acid

C₃H₆O₂ (Propanoic Acid)

Cₕ₂n+₁COOH

Ester

R-COO-R'

Carboxyl

-anoate

C₂H₃O₂ (Methyl Propanoate)

R-COO-R'

Amide

R-CONH₂

Amido

-anamide

C₃H₇NO (Propanamide)

Cₕ₂n+₁CONH₂

Amine

-NH₂

Amino

-anamine

C₂H₅NH₂ (Ethanamine)

Cₕ₂n₊₁NH₂

Halogenoalkane*

-F, -Cl, -Br, -I

Halogeno

prefix (fluoro, chloro, bromo, iodo)

C₂H₅Cl (Chloroethane)

Cₕ₂n₊₁X (Where X = F, Cl, Br, I)

Arene**

-C₆H₅

Phenyl

-benzene

C₆H₅CH₃ (Methylbenzene)

Guidelines for Naming Organic Compounds

Steps to Follow

  1. Choose Functional Groups: Identify functional groups to ascertain the class of the compound, focusing on any double or triple covalent bonds or groups containing oxygen (O) or nitrogen (N).

  2. Identify the Main Chain: Circle the longest continuous carbon chain that contains a functional group. This determines the parent structure.

  3. Identify Substituents: Name and count each substituent present in the molecule.

  4. Number the Carbon Atoms: Start numbering the carbon atoms in the main chain from the end closest to the functional group, ensuring proper location of substituents.

  5. Insert Locational Numbers: Place numbers to specify the location of functional groups within the name, e.g., butan-2-ol.

  6. Label Each Substituent: Use numbers before each substituent, even those on the same carbon, with specific exceptions outlined below:

    • Do not write '1' before the functional group for aldehydes and carboxylic acids as it is implicitly understood to be at position 1.

    • When a functional group or substituent has a single possible location, do not numerate it.

    • Example: methylpropane.

  7. Expression of Numbers and Words: Use proper separation techniques within the name such as:

    • Number, number

    • Number-word

    • Word-number

    • Word-word

  8. Alphabetical Order for Multiple Types of Substituents: When various types of substituents are present, they should be listed alphabetically while ignoring prefixes like mono-, di-, tri-, etc.

Naming Esters

  1. Identify the Longest Chain: Determine the longest continuous chain of carbon atoms inclusive of the ester linkage (COOC).

  2. Name the Alcohol Part: This is referred to as the alkyl part, which is the carbon chain single-bonded to the oxygen atom.

  3. Name the Acid Part: This is known as the alkanoate part, which is the carbon chain that ends with a C=O group, making sure to count the carbon in this group.

  4. Numbering: Start numbering from the ester linkage (C-O bond) outwards to locate any substituent attached to either part clearly.

Naming Ethers

  • Ethers are referred to as alkoxyalkanes, where the name reflects that the alkane involved has the most carbon atoms.