Question

Which of the following molecular formulas represents an alkyne? (a) \(\mathrm{C}_{10} \mathrm{H}_{20}\) (b) \(\mathrm{C}_{10} \mathrm{H}_{18}\)

Short answer

(b) \(\mathrm{C}_{10} \mathrm{H}_{18}\) represents an alkyne.

Step-by-step solution

Identify the type

An alkyne is a type of hydrocarbon that contains at least one carbon-carbon triple bond in its structure. Alkynes have the general formula \( ext{C}_n ext{H}_{2n-2}\) for non-cyclic compounds.

Compare formulas

Compare the given molecular formulas with the general formula of an alkyne. Check if either of the given formulas, \( ext{C}_{10} ext{H}_{20}\) or \( ext{C}_{10} ext{H}_{18}\), fits the pattern \( ext{C}_n ext{H}_{2n-2}\).

Verification

For \( ext{C}_{10}\), plug n=10 into the alkyne formula \( ext{C}_n ext{H}_{2n-2}\). This gives \( ext{C}_{10} ext{H}_{18}\), indicating that \( ext{C}_{10} ext{H}_{18}\) represents an alkyne. In contrast, \( ext{C}_{10} ext{H}_{20}\) matches the general formula \( ext{C}_n ext{H}_{2n}\) which corresponds to alkenes, not alkynes.

Key concepts

hydrocarbon chemistry

Hydrocarbon chemistry is a vast field that deals with compounds made exclusively of hydrogen and carbon. These compounds are the building blocks of essential substances such as oils, fuels, and even plastics. The family of hydrocarbons is categorically divided into alkanes, alkenes, alkynes, and aromatic hydrocarbons based primarily on the type of bonds between carbon atoms.

Alkanes contain only single bonds, alkenes boast at least one double bond, and alkynes include at least one triple bond. This difference in bonding dictates numerous chemical properties and reactivities of each type. Alkynes, due to their triple bond, tend to be more reactive than their single-bonded (alkane) and double-bonded (alkene) peers. Understanding this basic categorization is crucial to mastering hydrocarbon chemistry, as it leads to better comprehension of how these molecules behave and interact.

molecular formulas

A molecular formula provides specific details about the number of each type of atom in a molecule. In hydrocarbon chemistry, recognizing the structure through its molecular formula helps in identifying if a compound is an alkane, alkene, or alkyne.

For instance, alkynes follow the fundamental formula:

• Given by \(C_nH_{2n-2}\) for non-cyclic compounds.

The formula denotes that, for every "n" carbon atoms, there are \(2n-2\) hydrogen atoms. This reflects the additional bonding capacity due to the triple bond. On the contrary, alkenes that possess at least one double bond follow the formula \(C_nH_{2n}\), and alkanes have the general formula of \(C_nH_{2n+2}\).

Studying these formulas closely allows chemists to deduce the composition and general properties of a substance without the need for extensive experimentation. In the provided problem, \(C_{10}H_{18}\) neatly fits the alkyne formula, confirming it as an alkyne compound.

chemical structure recognition

Recognizing the chemical structure simply from a formula can be like solving a mystery. Chaining the correct atoms with appropriate bonding is what gives a molecule its characteristics.

With hydrocarbons, the focus is on recognizing the presence of single, double, or triple bonds. Alkynes, specifically, have unique traits due to their carbon-carbon triple bond. This bond results in specific molecular shapes and angles, affecting how they interact with other substances.

The chemical structure recognition not only aids in determining the family an organic compound belongs to but also helps predict their physical and chemical behaviors. By knowing that a molecular formula \(C_{10}H_{18}\) corresponds to an alkyne, we're able to anticipate properties such as boiling points, melting points, and even reactivity patterns. It’s all about connecting the dots between formula, structure, and behavior.