Question

Write a structural formula and a condensed structural formula for any two alkynes.

Short answer

Two alkynes: Ethyne (structural formula: H-C≡C-H, condensed: CH≡CH) and Propyne (structural formula: CH3-C≡C-H, condensed: CH3C≡CH).

Step-by-step solution

Understanding Alkynes

Alkynes are hydrocarbons with at least one carbon-carbon triple bond. Their general formula is CnH2n-2, where n is the number of carbon atoms. For the purpose of this exercise, we will choose ethyne and propyne to represent two alkynes with different numbers of carbon atoms.

Drawing the Structural Formula for Ethyne

Ethyne, also known as acetylene, has the molecular formula C2H2. The structural formula shows the atoms and the bonds between them. For ethyne, there are two carbon atoms connected by a triple bond, with each carbon atom also bonded to a single hydrogen atom. So the structural formula can be represented as H-C≡C-H, where '≡' indicates the triple bond.

Drawing the Structural Formula for Propyne

Propyne has the molecular formula C3H4. In the propyne molecule, two carbon atoms are bonded together with a single bond, and the third carbon forms a triple bond with one of the other carbon atoms. One of the end carbon atoms has three hydrogen atoms attached, and the other has one hydrogen. The structural formula is thus represented as CH3-C≡C-H.

Writing the Condensed Structural Formulas

Condensed structural formulas provide a simplified version of the structural formula. For ethyne, the condensed structural formula is simply CH≡CH, and for propyne, it is CH3C≡CH, omitting the bonds and showing each carbon atom and its directly associated hydrogens.

Key concepts

Hydrocarbons

Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen atoms. They represent the simplest form of organic compounds and serve as the foundational building blocks for more complex molecules. Hydrocarbons are classified into several types based on the bonds between carbon atoms: alkanes with single bonds, alkenes with double bonds, and alkynes with at least one triple bond.

Understanding hydrocarbons is crucial when studying organic chemistry, as they come in various structures and lengths, influencing their physical and chemical properties. Hydrocarbons are found abundantly in nature, specifically in crude oil and natural gas, and are widely used as fuels, lubricants, and raw materials for various chemical products.

Carbon-carbon triple bond

A carbon-carbon triple bond is a strong chemical bond where three pairs of electrons are shared between two carbon atoms. This type of bond is denoted by the symbol '≡' and is a defining feature of alkynes, one of the main groups of hydrocarbons. The triple bond gives alkynes distinct characteristics, such as a linear structure around the bonded carbons and a higher degree of unsaturation compared to alkanes and alkenes.

These triple bonds are highly reactive, making alkynes useful in various chemical reactions. For example, the alkyne ethyne (acetylene) is widely used in welding because of the high temperatures produced when it combusts. The presence of this bond greatly influences the molecule's reactions, such as undergoing addition reactions to form more complex compounds.

Molecular formula

The molecular formula of a compound provides the exact number of each type of atom present in a single molecule. For example, in the alkyne ethyne, the molecular formula is C₂H₂, indicating that each molecule consists of two carbon atoms and two hydrogen atoms. Likewise, the molecular formula for propyne is C₃H₄, showing three carbon atoms and four hydrogen atoms per molecule.

The molecular formula is crucial for understanding the composition of a compound but does not convey information about the arrangement or bonding of atoms. For a more in-depth understanding of a molecule's structure, one would rely on the structural or condensed structural formula.

Structural formula

The structural formula illustrates how atoms in a molecule are connected, including the bonds between them. It provides a visual representation, showing single, double, or triple bonds and the arrangement of atoms within the molecule. For instance, the structural formula for ethyne illustrates the carbon atoms connected by a triple bond with each carbon also bonded to a hydrogen atom, represented as H–C≡C–H.

The structural formula reveals more than just the composition; it sheds light on the molecule's geometry and can provide insight into its reactivity. For educational purposes, it helps students visualize how the atoms in a molecule are bonded, which is critical when studying the reactions and properties of different compounds.

Condensed structural formula

The condensed structural formula is a simplified representation of a molecule's structure, showing the arrangement of atoms without explicitly drawing all bonds. It summarizes the molecular structure by grouping each carbon atom with its directly attached hydrogens. For example, the condensed structural formula for ethyne is CH≡CH, which conveys the same information as the structural formula but in a more compact form.

Condensed formulas are particularly useful when dealing with larger organic molecules, as they provide a clear and concise way to present complex structures. They are important in both academic settings and practical chemical notation, as they allow chemists to quickly communicate essential structural information without resorting to lengthy and detailed drawings.