Question

The compounds having all atoms in a plane in all conformations (if possible) are (A) But-1-ene (B) But- 1 -en-3-yne (C) Buta-1,3-diene (D) Buta- 1,3 -diyne

Short answer

The compounds having all atoms in a plane in all conformations (if possible) are: (A) But-1-ene, (B) But-1-en-3-yne, and (D) Buta-1,3-diyne. These compounds have either single bonds, restricted double bonds, or triple bonds that prevent free rotation, keeping all atoms in the same plane.

Step-by-step solution

Analyze the structure of But-1-ene

But-1-ene has the molecular formula CH2=CH-CH2-CH3. The carbon-carbon double bond consists of a sigma bond and a pi bond, restricting rotation around the bond. This means But-1-ene is planar as all carbon atoms are connected by single or restricted double bonds.

Analyze the structure of But-1-en-3-yne

But-1-en-3-yne has the molecular formula CH2=CH-C≡CH. In this molecule, the carbon-carbon double bond (C=C) restricts rotation due to its pi bond. The carbon-carbon triple bond (C≡C) has two pi bonds, also restricting rotation around the bond. Therefore, all atoms in But-1-en-3-yne are in the same plane.

Analyze the structure of Buta-1,3-diene

Buta-1,3-diene has the molecular formula CH2=CH-CH=CH2. This molecule has two carbon-carbon double bonds present. Although a single double bond restricts rotation, the rotation is only restricted around the specific carbon-carbon double bond. In Buta-1,3-diene, the carbon atoms containing the C=C have rotational freedom around the single bond (C-C) between them. As a result, all atoms in Buta-1,3-diene do not stay in the same plane in all conformations.

Analyze the structure of Buta-1,3-diyne

Buta-1,3-diyne has the molecular formula CH≡C-C≡CH. This molecule possesses two carbon-carbon triple bonds. The triple bonds (C≡C) restrict rotation, due to their pi bonds. As there is no free rotation around the triple bonds, all atoms in Buta-1,3-diyne are in the same plane.

Identify planar compounds

From the analysis of each compound, we can conclude that the compounds having all atoms in a plane in all conformations (if possible) are: (A) But-1-ene (B) But- 1 -en-3-yne (D) Buta- 1,3 -diyne

Key concepts

Carbon-Carbon Double Bond

In organic chemistry, carbon-carbon double bonds are crucial in establishing a molecule's geometry. A double bond between two carbon atoms (denoted as C=C) consists of one sigma (σ) bond and one pi (π) bond. The sigma bond is the primary bond that holds the carbon atoms together, while the pi bond arises from the overlap of p orbitals. This overlap creates an electron cloud both above and below the plane of the atoms, locking the molecular conformation.

Due to the presence of the pi bond, rotation around a double bond is greatly restricted. This restriction means that the atoms linked by the double bond generally remain in a plane, leading to a planar structure, as observed in compounds like But-1-ene. In such cases, all atoms in the molecule may reside in the same geometric plane.

Carbon-Carbon Triple Bond

The carbon-carbon triple bond (denoted as C≡C) is a feature of certain organic compounds that significantly affects their spatial arrangement. A triple bond comprises one sigma bond and two pi bonds. The sigma bond forms the primary connection between the two carbon atoms, while the two pi bonds are arranged perpendicularly, wrapping around the sigma bond.

This bond arrangement restricts any rotational movement about the bond, thereby enforcing a linear geometry at the site of the triple bond. Because of this linear nature, compounds like Buta-1,3-diyne, which feature triple bonds, often exhibit all atoms arranged in a single plane. The rigidity and linearity are due to the constraints imposed by the two overlapping pi bonds that restrict movement in space.

Molecular Geometry

Molecular geometry is a key concept in understanding the three-dimensional arrangement of atoms in a molecule. It is influenced primarily by the types of bonds between the atoms, such as single, double, or triple bonds, which determine the molecule's flexibility and shape.

For example, a carbon-carbon double bond typically results in a planar structure, as seen in But-1-ene, due to the restricted rotation around these bonds. Similarly, the presence of triple bonds, like in But-1-en-3-yne and Buta-1,3-diyne, leads to linear arrangements, which also ensure planarity. Buta-1,3-diene, while possessing double bonds, does not maintain planarity in all conformations due to the rotational freedom around single bonds between the double bonds.

Understanding molecular geometry helps predict the structural and chemical properties of organic compounds, demonstrating the interplay between bond types and spatial configuration.

Sigma and Pi Bonds

Sigma (σ) and pi (π) bonds are fundamental in defining the structure and properties of organic compounds. A sigma bond is the strongest type of covalent bond, formed by the head-on overlap of atomic orbitals, allowing free rotation of atoms around the bond unless other bonds restrict it.

On the other hand, a pi bond is formed by the sideways overlap of p orbitals. This overlap creates an electron density above and below the axis of the bonded atoms. Each double bond contains one pi bond, while each triple bond contains two pi bonds. These pi bonds restrict rotation and significantly influence the geometry of molecules.

For example, in But-1-en-3-yne, the carbon-carbon double and triple bonds restrict rotation due to their pi bonds, ensuring a planar structure. Understanding sigma and pi bonds aids in predicting molecular configurations and properties, offering insight into the behavior of organic molecules.