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A topic from the subject of Nomenclature in Chemistry.

  • 1 year ago
  • 6 min read

Nomenclature of Organic Compounds

Introduction

Organic compounds are molecules containing carbon and hydrogen atoms. They form the basis of all living things and are found in various substances, including drugs, plastics, and food. Organic compounds are categorized into groups based on their structure. Three primary groups are alkanes, alkenes, and alkynes. Alkanes are hydrocarbons with only single bonds between carbon atoms. Alkenes have at least one double bond, and alkynes have at least one triple bond between carbon atoms.

Nomenclature of Alkanes

Alkane names originate from Greek words representing the number of carbon atoms. The prefixes are shown below:

Number of Carbon Atoms Prefix
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-

An alkane's name is the prefix for its carbon atom count followed by "-ane". For example, propane has three carbon atoms.

Nomenclature of Alkenes

Alkenes' names are derived from the number of carbon atoms and the presence of a double bond. The prefixes are:

Number of Carbon Atoms Prefix
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-

The name is the prefix followed by "-ene". If the double bond is between the second and third carbons, use "1-ene". For instance, propene has a double bond between the first and second carbons, while 1-propene has it between the second and third.

Nomenclature of Alkynes

Alkyne names are derived from the number of carbon atoms and the presence of a triple bond. Prefixes are:

Number of Carbon Atoms Prefix
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-

The name is the prefix followed by "-yne". The position of the triple bond is indicated similarly to alkenes (e.g., 1-butyne).

Nomenclature of Alcohols

Alcohols contain a hydroxyl (-OH) group. The naming convention uses the alkane name with the suffix "-ol". The position of the hydroxyl group is indicated by a number (e.g., 2-propanol).

Nomenclature of Aldehydes

Aldehydes contain a formyl group (-CHO) at the end of a carbon chain. The naming convention uses the alkane name with the suffix "-al" (e.g., ethanal).

Nomenclature of Ketones

Ketones contain a carbonyl group (C=O) within the carbon chain. The naming convention uses the alkane name with the suffix "-one". The position of the carbonyl group is indicated by a number (e.g., 2-butanone).

Nomenclature of Carboxylic Acids

Carboxylic acids contain a carboxyl group (-COOH). The naming convention uses the alkane name with the suffix "-oic acid" (e.g., ethanoic acid).

Nomenclature of Alcohols, Aldehydes, Ketones, Carboxylic Acids
Alcohols
- Suffix: -ol
- The longest carbon chain containing the hydroxyl group (-OH) is identified as the parent chain.
- The carbon chain is numbered to give the hydroxyl group the lowest possible number. This number is included as a locant before the parent alkane name.
- Example: CH3CH2OH (ethanol)
- Example with branching: CH3CH(OH)CH2CH3 (2-butanol)
Aldehydes
- Suffix: -al
- The carbonyl group (C=O) is always at the end of the carbon chain and is assigned position 1.
- Example: CH3CHO (ethanal)
- Example with branching: CH3CH(CH3)CH2CHO (3-methylbutanal)
Ketones
- Suffix: -one
- The carbonyl group (C=O) is located within the carbon chain.
- The longest carbon chain containing the carbonyl group is identified as the parent chain.
- The carbon chain is numbered to give the carbonyl group the lowest possible number. This number is included as a locant before the parent alkane name.
- Example: CH3COCH3 (propanone or acetone)
- Example with branching: CH3COCH2CH3 (butan-2-one)
Carboxylic Acids
- Suffix: -oic acid
- The carboxyl group (-COOH) is always at the end of the carbon chain and is assigned position 1.
- Example: CH3COOH (ethanoic acid or acetic acid)
- Example with branching: CH3CH(CH3)CH2COOH (3-methylbutanoic acid)
Key Points:
- The base name of the compound is determined by the longest carbon chain containing the functional group.
- The suffix indicates the type of functional group present.
- The carbon chain is numbered to give the functional group the lowest possible number. This number is used as a locant.
- Numbering always starts from the end of the chain closest to the principal functional group (the one that determines the suffix).
- Carboxylic acids are prioritized over alcohols, aldehydes, and ketones in terms of naming.
- For molecules containing multiple functional groups, IUPAC prioritization rules determine the principal functional group and suffix.
Experiment: Nomenclature of Alcohols, Aldehydes, Ketones, Carboxylic Acids
Objective:

To practice naming alcohols, aldehydes, ketones, and carboxylic acids using IUPAC nomenclature.

Materials:
  • Whiteboard or chart paper
  • Markers
  • List of organic compounds (with structures)
    • Example 1: CH3CH2OH (Ethanol)
    • Example 2: CH3CHO (Ethanal)
    • Example 3: CH3COCH3 (Propanone)
    • Example 4: CH3COOH (Ethanoic acid)
Procedure:
  1. Draw the structure of each organic compound on the whiteboard or chart paper.
  2. Identify the longest carbon chain containing the functional group.
  3. Number the carbon atoms in the longest chain, starting from the end closest to the functional group.
  4. Name the substituents (alkyl groups or other functional groups) and their positions on the carbon chain.
  5. Arrange the substituents alphabetically.
  6. Use IUPAC nomenclature rules to assign a name to each compound. (e.g., for alcohols use the suffix -ol, for aldehydes -al, for ketones -one, and for carboxylic acids -oic acid)
  7. Write the names of the compounds on the whiteboard or chart paper.
Key Procedures:
  • Identifying the functional group(s) present in each compound is crucial for naming the compound correctly.
  • IUPAC nomenclature rules must be followed carefully to ensure that the names are consistent and accurate. Pay close attention to numbering the carbon chain and alphabetizing substituents.
  • Consider the priority of functional groups when multiple are present in the molecule.
Significance:

This experiment helps students develop a strong understanding of the nomenclature of alcohols, aldehydes, ketones, and carboxylic acids. This knowledge is essential for communication in the field of chemistry, as well as for understanding the properties and reactions of these important organic compounds.

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