Question

For correct IUPAC name \(\mathrm{P}_{1}\)-methyl pent- \(\mathrm{P}_{2}\)-yne. How many pairs of \(\left(\mathrm{P}_{1}, \mathrm{P}_{2}\right)\) are possible? (A) 2 (B) 1 (C) \(\infty\) (D) 3

Short answer

The number of possible pairs (P1, P2) for the given IUPAC name, P1-methyl pent-P2-yne, is only one. Applying the IUPAC rules for naming alkenes, the correct pair is (P1, P2) = (3, 2), making the answer (B) 1.

Step-by-step solution

Analyze the given IUPAC name

The IUPAC name given is P1-methyl pent-P2-yne, which means there is a methyl group attached at position P1 and a triple bond beginning at position P2 within a 5 carbon chain (pent- refers to the 5-carbon chain). Now, we need to apply the IUPAC rules to find the valid pair(s) of positions.

Identify IUPAC Rules for Naming Alkenes

In IUPAC nomenclature, we have to follow these rules when naming alkenes: 1. The numbering of carbon atoms must start from the end that gives the first point of difference (functional groups or substituents) the lowest possible number. 2. When assigning position numbers to substituents, choose the smallest possible numbers. 3. Double and triple bonds take priority over alkyl groups when assigning position numbers. 4. The "yne" suffix indicates a triple bond, which means that we cannot have a 1-yne as that would denote a triple bond at the first carbon, which is not possible.

Apply IUPAC Rules to given Alkene

Applying the IUPAC rules mentioned above, let's find the possible pairs for the given IUPAC name. 1. Since the "yne" takes priority over the methyl group, we will assign the lowest possible number to the triple bond starting position P2. 2. As mentioned earlier, we cannot have a 1-yne, so P2 must be 2. 3. With a triple bond starting at position 2, the compound has the following structure: CH─C≡C─CH_2─CH_3. 4. The methyl group must be attached to a carbon other than the first one and the last one since the first carbon is already part of a triple bond and the last one has already three Hydrogen atoms. 5. So, only one possible position is remaining for the methyl group: on the third carbon, which will be the position P1.

Determine the number of possible pair(s)

Based on our analysis, there is only one possible pair that satisfies the IUPAC rules: (P1, P2) = (3, 2). The correct answer is therefore (B) 1.

Key concepts

Alkyne Nomenclature

Alkynes are a type of hydrocarbon that contain carbon-carbon triple bonds and are denoted by the suffix "yne" in IUPAC nomenclature. When naming alkynes, it is crucial to identify the longest carbon chain that includes the triple bond. This chain dictates the base name of the compound, which is derived from the number of carbons in the chain, such as "pent" for five carbons.

• Locate the longest carbon chain containing the triple bond.
• Number the chain from the end that gives the triple bond the lowest number possible.
• The position where the triple bond starts is indicated by the smallest locant possible.
• For example, "pent-2-yne" suggests a five-carbon chain with the triple bond starting at the second carbon.

By following these steps, the correct structure and naming according to IUPAC rules can be established. Ensuring the accurate identification of the alkyne within the compound is essential for proper communication in organic chemistry.

Organic Chemistry

Organic chemistry is the branch of chemistry that studies the structure, properties, and reactions of organic compounds which primarily contain carbon atoms. These compounds can include a variety of other elements, most commonly hydrogen, oxygen, nitrogen, sulfur, and halogens. In organic chemistry, understanding the reactivity and interactions of different functional groups is vital.
Carbon’s ability to form stable covalent bonds with other carbon atoms opens the door to a vast array of molecular geometries and organic compounds.

• Functional groups such as alcohols, amines, carboxylic acids, and alkynes impart specific chemical reactivity to organic molecules.
• Organic reactions often involve the making or breaking of carbon-carbon bonds or carbon-heteroatom bonds.
• The role of the organic chemist is often to synthesize or modify organic molecules to enhance their usefulness in pharmaceuticals, materials science, and more.

By understanding the principles of organic chemistry, one can predict and manipulate chemical reactions that are pivotal in both natural systems and industrial applications.

Functional Groups

In organic chemistry, functional groups are specific groups of atoms within molecules that have characteristic and distinct chemical behaviors. They are the centers of reactivity in the molecule. Recognizing these groups is critical as they dictate the types of reactions that a compound can undergo.
Each functional group will undergo the same type of reactions, regardless of the molecule it is part of.

• A few important functional groups include hydroxyl groups (-OH), carbonyl groups (C=O), amino groups (-NH_2), and the triple bond characteristic of alkynes.
• The alkyne functional group is identified by a carbon-carbon triple bond, which significantly impacts the molecule's chemistry by providing unsaturation and reactive sites.
• These reactive sites are what chemists target when performing chemical transformations.

By learning to identify and understand functional groups, you can gain insights into how chemical compounds will react, which is fundamental in both synthesis and breakdown processes in chemistry.

Substituents Positioning

Substituents in organic chemistry are atoms or groups of atoms that are attached to the main chain or ring of a carbon-based molecule. The positioning of substituents on the carbon chain can greatly affect the chemical properties and naming conventions of the compound.
Determining the position of substituents accurately is crucial for correct IUPAC naming.

• Number the longest continuous chain of carbon atoms in the molecule from the end nearest to the first point of branching or functional group.
• Assign the lowest possible numbers to the substituents based on their position along the carbon chain.
• In the compound "3-methyl pent-2-yne," the "3" indicates the position of the methyl group, while "2" refers to the start of the triple bond.
• Ensuring the lowest positional numbers helps minimize ambiguity and provides clarity in structural representation.

By mastering the principles of substituents positioning, you can ensure correct molecular representation and facilitate effective communication in science and engineering contexts.