IUPAC Nomenclature: Naming Alkanes

• IUPAC (International Union of Pure and Applied Chemistry) nomenclature is a standardized system for naming chemical compounds.
• It ensures each compound has a unique, systematic name reflecting its structure and composition.

Fundamentals of IUPAC Naming System

• The IUPAC system involves three fundamental steps: identifying the parent chain, numbering the chain, and naming substituents & functional groups.
• Identifying the Parent Chain: Select the longest continuous chain of carbon atoms.
• Numbering the Chain: Assign numbers to carbon atoms based on priority rules.
• Naming Substituents & Functional Groups: Use prefixes, suffixes, and locants to name the compound.

Types of Chemical Compounds & Their Nomenclature

• IUPAC nomenclature varies for different classes of compounds.

Naming Alkanes (Saturated Hydrocarbons)

• Alkanes are saturated hydrocarbons containing only single bonds, with a general formula of CₙH₂ₙ₊₂.

Rules for Naming Alkanes

• Identify the longest continuous carbon chain and name it using the root word: Meth- (1C), Eth- (2C), Prop- (3C), But- (4C), Pent- (5C), Hex- (6C), Hept- (7C), Oct- (8C), Non- (9C), Dec- (10C).
• Number the chain from the end nearest to a substituent.
• Name and number substituents (alkyl groups like methyl, ethyl, propyl).
• For multiple identical substituents, use prefixes like di-, tri-, tetra- (e.g., 2,2-dimethylbutane).
• Arrange different substituents alphabetically, ignoring prefixes like di-, tri-.
• Example: 2-Methylpentane is a five-carbon chain with a methyl group at position 2.

Naming Alkenes & Alkynes (Unsaturated Hydrocarbons)

• Alkenes (C=C) and alkynes (C≡C) are unsaturated hydrocarbons.

Rules for Naming Alkenes & Alkynes

• Find the longest carbon chain containing the double/triple bond.
• Number the chain so that the double/triple bond gets the lowest possible number.
• Use suffixes: -ene for alkenes (e.g., Ethene for C₂H₄), -yne for alkynes (e.g., Ethyne for C₂H₂).
• If multiple bonds are present, use numbers and prefixes like diene, diyne.
• Example: But-2-ene has a double bond between C2 and C3 in a four-carbon chain.

Naming Cycloalkanes

• Cycloalkanes are ring-shaped alkanes.

Rules for Naming Cycloalkanes

• Use the prefix "cyclo-" before the parent alkane name.
• Numbering starts at the highest priority substituent.
• Example: Cyclopentane is a five-membered carbon ring.

Naming Aromatic Compounds

• Aromatic compounds contain benzene rings.

Rules for Naming Aromatic Compounds

• Use benzene as the parent chain (e.g., methylbenzene for toluene).
• Number substituents to give the lowest sum.
• Special names exist for common compounds like Toluene (Methylbenzene), Phenol (Hydroxybenzene), and Aniline (Aminobenzene).
• Example: 1,3-Dimethylbenzene has two methyl groups on the benzene ring at positions 1 and 3.

Naming Functional Groups in Organic Compounds

• Functional groups determine the properties of compounds.

Priority Order of Functional Groups (Highest to Lowest)

• Carboxyl (-COOH): Suffix -oic acid (e.g., Ethanoic acid).
• Ester (-COO-): Suffix -oate (e.g., Methyl ethanoate).
• Aldehyde (-CHO): Suffix -al (e.g., Propanal).
• Ketone (-CO-): Suffix -one (e.g., Butanone).
• Alcohol (-OH): Suffix -ol (e.g., Ethanol).
• Amine (-NH₂): Suffix -amine (e.g., Propan-2-amine).
• Alkene (-C=C-): Suffix -ene (e.g., Butene).
• Alkyne (-C≡C-): Suffix -yne (e.g., Ethyne).

General Rules for Functional Groups

• The highest priority group is designated as the suffix, while others are used as prefixes.
• The carbon chain is numbered so that the highest priority group has the lowest number.
• For multiple functional groups, use appropriate prefixes (e.g., hydroxy, oxo, amino) along with the main suffix.