Question

Name each of the following alkynes: a. \(\mathrm{CH}_{3} \mathrm{C}=\mathrm{CCH}_{2} \mathrm{CH}_{3}\) b. \(\mathrm{CH}=\mathrm{CH}\)

Short answer

The names of the alkynes are (a) pent-2-yne and (b) ethyne.

Step-by-step solution

Identify the Longest Carbon Chain Containing the Alkyne

For molecule (a), the longest chain containing the triple bond has five carbons. For molecule (b), the alkyne is the longest chain and has two carbons.

Number the Carbon Chain

Number the carbon atoms in the chain starting from the end nearest to the triple bond. For molecule (a), number the chain from left to right to give the triple bond the lowest possible number. For (b), numbering can begin from either end since the chain is symmetrical.

Apply the IUPAC Naming Rules for Alkynes

Use the base name of the alkane corresponding to the number of carbons in the longest chain, but replace the 'ane' ending with 'yne' to denote an alkyne. For (a), since the triple bond starts from the second carbon, it is named pent-2-yne. For (b), the compound is called ethyne.

Include Numerical Locants for Substituents if Needed

No substituents are present in molecule (a), only methyl groups at the ends which are included in the main chain. For molecule (b), there are no substituents, so no numerical locants are needed.

Key concepts

Organic Chemistry and Alkynes

In the world of organic chemistry, the study of carbon-containing compounds is fundamental, with a diversity of structures and functions that make up an endless array of organic molecules. Alkynes represent a significant class of hydrocarbons characterized by a carbon–carbon triple bond, giving these compounds unique properties and reactivities.

Understanding the structure of alkynes is critical, as each variation in the bond or substituents can lead to drastically different compounds with various applications in industry, pharmaceuticals, and academia. These triple bonds are not only pivotal in the chemical characteristics of the compound but also in how they interact with other molecules. Further knowledge about alkynes extends to their synthesis and reactions, vital for students aspiring to work in organic synthesis or related fields.

IUPAC Naming

Navigating the complexities of molecular structures requires a standardized system for naming. IUPAC naming is the universally accepted method, designed to convey detailed structural information through a compound's name. This systematic approach ensures that each unique structure is paired with a unique name.

Step-by-Step Nomenclature of Alkynes

• Identify the longest chain of carbon atoms containing the highest-order bond (triple bond in alkyne).
• Assign a number to each carbon in the chain, starting at the end closest to the triple bond, to give it the lowest possible locant.
• Select the proper base name associated with the number of carbon atoms in the chain, substituting the ending '-ane' with '-yne' for alkynes.
• Add locants for substituents or branches, if any are present, to indicate their position on the chain.

Following these rules ensures clear and consistent communication among scientists, vital for collaboration and progression in the field of organic chemistry.

Chemical Structures

The representation and understanding of chemical structures stand at the core of organic chemistry. A chemical structure not only delineates which atoms are present in a molecule but also shows how these atoms are connected to each other and the types of bonds between them. In alkyne nomenclature, identifying the chemical structure is paramount as it dictates the name of the compound.

Importance of Structure in Naming

For alkynes, the position of the triple bond within a carbon chain impacts the naming significantly, as seen in the provided exercise. The structure-to-name translation that follows IUPAC guidelines reflects the molecule's construction and can hint at its physical and chemical properties. Such clarity in structure recognition and naming is essential, as it allows chemists to predict reactivity patterns, synthesize new compounds systematically, and analyze the behavior of molecules in various conditions.