# Nomenclature of Aliphatic Organic Compounds This section outlines the systematic method for naming aliphatic organic compounds as established by the International Union of Pure and Applied Chemistry (IUPAC). Aliphatic compounds include straight-chain, branched-chain, and non-aromatic cyclic molecules, which can be saturated or unsaturated. For naming to work properly, you must first understand what functional groups are. A is a specific atom or group of atoms that determines the chemical properties of a compound. --- ## Key Information - **Systematic Names**: The systematic names for most homologous series (except carboxylic acids) are written as a single word. - **Trivial Names**: Non-systematic or common names (e.g., acetone, formaldehyde) are still used in many contexts. - **IUPAC**: The International Union of Pure and Applied Chemistry provides internationally accepted rules for chemical nomenclature. --- ### 15.4.1 Nomenclature of Alkanes Alkanes form the foundation for naming all other organic compounds. Their nomenclature rules are the starting point. #### Common (Trivial) Names of Alkanes Simple alkanes may have common names, such as *neopentane*. #### Systematic (IUPAC) Names of Alkanes The following rules are applied to assign systematic names to alkanes: 1. **Identify the Parent Chain**: - Find the longest continuous chain of carbon atoms. This chain determines the *root name* of the alkane (e.g., 7 carbons = heptane). - The suffix for all alkanes is **-ane**. - Example: The structure below has a 7-carbon parent chain, so its root name is **heptane**. $$\mathrm{CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3}$$ 2. **Identify and Number Substituents**: - Groups attached to the parent chain are called *substituents* or *side chains* (e.g., alkyl groups like methyl, ethyl). - Number the parent chain from the end that gives the substituents the **lowest possible locant numbers**. - The locant is the number of the carbon atom on the parent chain to which the substituent is attached. 3. **Handle Multiple Identical Substituents**: - Use prefixes like *di-*, *tri-*, *tetra-* to indicate how many identical substituents are present. - Each substituent must have its own locant number, even if they are on the same carbon. Separate locants with commas. - Examples: - **3,3-dimethylheptane**: Two methyl groups on carbon 3. - **3,4-dimethylheptane**: One methyl group on carbon 3 and another on carbon 4. - **3,3,5-trimethyloctane**: Three methyl groups, two on carbon 3 and one on carbon 5. 4. **Handle Multiple Different Substituents**: - List the substituents in **alphabetical order** (ignoring prefixes like di-, tri-). - Each substituent is preceded by its locant number. - Example: - **5-ethyl-3-methyloctane**: 'ethyl' comes before 'methyl' alphabetically. --- ### 15.4.2 Nomenclature of Cycloalkanes 1. **Base Name**: The name of the corresponding open-chain alkane is prefixed with **cyclo-**. - *Examples*: cyclopropane, cyclopentane, cyclohexane. 2. **Substituted Cycloalkanes**: - Substituents are named as prefixes. - If there is one substituent, no number is needed. - If there are multiple substituents, number the ring to give the locants the lowest possible values at the first point of difference. List them alphabetically. - *Examples*: - **1-ethyl-2-methylcyclopropane** - **1,1,3-trimethylcyclohexane** - **2-ethyl-1,1-dimethylcyclopentane** --- ### 15.4.3 Nomenclature of Alkenes and Alkynes Alkenes (double bonds) and alkynes (triple bonds) have specific rules for their functional groups. 1. **Parent Chain**: The parent chain **must contain** the multiple bond(s). The suffix is **-ene** for alkenes and **-yne** for alkynes. 2. **Numbering**: Number the chain from the end closer to the multiple bond to give it the lowest possible locant. The locant is placed just before the suffix. - *Examples*: - $\mathrm{CH_2=CH_2}$ is **ethene**. - $\mathrm{CH_3-CH=CH_2}$ is **propene**. - **4-methylpent-1-ene** - **5-methylhex-1-yne** 3. **Multiple Double/Triple Bonds**: - If more than one multiple bond is present, add an "a" to the root name (e.g., but**a**ne). - Use prefixes *di-*, *tri-* before the -ene or -yne suffix. - *Examples*: - **2-methylbuta-1,3-diene** - **3-methylhexa-1,5-diyne** 4. **Compounds with Both Double and Triple Bonds**: - The ending is **-en-yne**. - Number from the end closer to the first multiple bond, regardless of type. - If there is a tie, the **double bond** gets the lower number. - *Examples*: - **4-methyloct-1-en-7-yne** - **4-ethylhex-1-en-5-yne** --- ### 15.4.4 Nomenclature of Halogenoalkanes Halogenoalkanes (or alkyl halides) treat the halogen atom as a substituent (halo group). For more on halogens, see . - **Prefixes**: *fluoro-*, *chloro-*, *bromo-*, *iodo-*. - **Numbering**: Number the parent chain to give the halogen atom the lowest possible locant. - **Common Names**: Often named as *alkyl halides*. - **Examples**: - $\mathrm{CH_3-I}$: **iodomethane** [methyl iodide] - $\mathrm{CH_3CH_2Cl}$: **chloroethane** [ethyl chloride] - $\mathrm{CH_3CH(Cl)CH_3}$: **2-chloropropane** [isopropyl chloride] - $\mathrm{CH_3CH(CH_3)CH_2-Br}$: **1-bromo-2-methylpropane** [isobutyl bromide] - $\mathrm{C(CH_3)_3Br}$: **2-bromo-2-methylpropane** [tert-butyl bromide] --- ### 15.4.5 Nomenclature of Alcohols Alcohols contain the hydroxyl (-OH) functional group. - **Suffix**: Replace the "-e" of the corresponding alkane with **-ol**. - **Numbering**: Number the parent chain to give the hydroxyl group the lowest possible locant. The locant precedes the "-ol" suffix. - **Polyhydric Alcohols**: If there are multiple -OH groups, use suffixes like *-diol*, *-triol*. The "-e" from the alkane name is retained (e.g., ethane**diol**). - **Alkenols**: Compounds with both a double bond and a hydroxyl group. The -OH group takes priority for numbering. The name ends in **-en-ol**. - **Examples**: - $\mathrm{CH_3OH}$: **methanol** - $\mathrm{CH_3CH_2OH}$: **ethanol** - **Pentan-2-ol** - **2-methylpropan-2-ol** [tert-butyl alcohol] - **Ethane-1,2-diol** [ethylene glycol] - **Propane-1,2,3-triol** [glycerol] - $\mathrm{CH_2=CH-CH_2-OH}$: **prop-2-en-1-ol** [allyl alcohol] --- ### 15.4.6 Nomenclature of Aldehydes Aldehydes contain the terminal carbonyl group (-CHO). - **Suffix**: Replace the "-e" of the corresponding alkane with **-al**. - **Numbering**: The aldehyde carbon is always **carbon 1**. Its position is not explicitly stated in the name. - **Examples**: - $\mathrm{HCHO}$: **methanal** [formaldehyde] - $\mathrm{CH_3CHO}$: **ethanal** [acetaldehyde] - **3-methylbutanal** --- ### 15.4.7 Nomenclature of Ketones Ketones contain a non-terminal carbonyl group (-CO-). - **Suffix**: Replace the "-e" of the corresponding alkane with **-one**. - **Numbering**: Number the parent chain to give the carbonyl carbon the lowest possible locant. The locant precedes the "-one" suffix. - **Examples**: - $\mathrm{CH_3COCH_3}$: **propanone** [acetone] - $\mathrm{CH_3COCH_2CH_3}$: **butanone** [ethyl methyl ketone] - **2-methylpentan-3-one** --- ### 15.4.8 Nomenclature of Ethers Ethers are named as **alkoxyalkanes**. - **Naming**: The smaller alkyl group + oxygen is named as an **alkoxy-** prefix. The larger alkyl group forms the parent alkane name. - **Examples**: - $\mathrm{CH_3-O-CH_3}$: **methoxymethane** [dimethyl ether] - $\mathrm{CH_3-O-CH_2CH_3}$: **methoxyethane** [ethyl methyl ether] - $\mathrm{CH_3CH_2-O-CH_2CH_3}$: **ethoxyethane** [diethyl ether] --- ### 15.4.9 Nomenclature of Amines Amines are derivatives of ammonia ($\mathrm{NH_3}$). - **Primary Amines**: Suffix **-amine** replaces the "-e" of the alkane name. The amino group ($\mathrm{NH_2}$) is located with a number. The name is **alkanamine**. - $\mathrm{CH_3NH_2}$: **methanamine** - $\mathrm{CH_3CH_2CH_2NH_2}$: **propan-1-amine** - **Secondary and Tertiary Amines**: The largest alkyl group is the parent chain. Other alkyl groups on the nitrogen atom are treated as substituents, with the locant **N-**. - **N-methylethanamine** - **N-ethyl-N-methylpropan-1-amine** --- ### 15.4.10 Nomenclature of Nitriles Nitriles contain the cyano group (-CN). - **Suffix**: Add **-nitrile** to the name of the alkane chain that includes the carbon of the -CN group. The "-e" of the alkane is retained. - **Numbering**: The nitrile carbon is always **carbon 1**. - **Examples**: - $\mathrm{CH_3CN}$: **ethanenitrile** [acetonitrile] - $\mathrm{CH_3CH_2CN}$: **propanenitrile** [propionitrile] - $\mathrm{CH_3CH_2CH_2CN}$: **butanenitrile** --- ### 15.4.11 Nomenclature of Carboxylic Acids Carboxylic acids contain the carboxyl group (-COOH). - **Suffix**: Replace the "-e" of the corresponding alkane with **-oic acid**. - **Numbering**: The carboxyl carbon is always **carbon 1**. - **Examples**: - $\mathrm{HCOOH}$: **methanoic acid** [formic acid] - $\mathrm{CH_3COOH}$: **ethanoic acid** [acetic acid] - $\mathrm{(COOH)_2}$: **ethanedioic acid** [oxalic acid] --- ### 15.4.12 Nomenclature of Esters Esters are derivatives of carboxylic acids. - **Naming**: The name is two words. 1. The first word is the name of the **alkyl group** from the alcohol part. 2. The second word is the name of the carboxylate part, where the "-oic acid" of the parent acid is replaced with **-oate**. - **Examples**: - $\mathrm{HCOOCH_3}$: **methyl methanoate** [methyl formate] - $\mathrm{CH_3COOCH_3}$: **methyl ethanoate** [methyl acetate] - $\mathrm{CH_3COOCH(CH_3)_2}$: **1-methylethyl ethanoate** [isopropyl acetate] --- ### 15.4.13 Nomenclature of Acid Chlorides Acid chlorides (or acyl chlorides) are derivatives of carboxylic acids. - **Suffix**: Replace the "-oic acid" of the parent acid with **-oyl chloride**. - **Examples**: - $\mathrm{CH_3COCl}$: **ethanoyl chloride** [acetyl chloride] - $\mathrm{CH_3CH_2COCl}$: **propanoyl chloride** [propionyl chloride] --- ### 15.4.14 Nomenclature of Amides Amides are derivatives of carboxylic acids. - **Primary Amides**: Replace "-oic acid" of the parent acid with **-amide**. - $\mathrm{HCONH_2}$: **methanamide** [formamide] - $\mathrm{CH_3CONH_2}$: **ethanamide** [acetamide] - **Secondary and Tertiary Amides**: Alkyl groups on the nitrogen are named as substituents with the locant **N-**. - **N-methylethanamide**

15.4 Nomenclature Of Aliphatic Organic Compounds | Organic Chemistry | Chemistry 11