Chapter 5, Problem 5.81MP

(a)

Interpretation Introduction

Interpretation:

The three possible structures for $C_2{H}_{2}C{l}_2$ and the overall shape and their difference in shape should be explained.

Concept introduction:

• Using VSEPR theory and Lewis structure, the exact geometry of a molecule can be obtained.
• In VSEPR, the geometry of the molecule is explained based on minimizing electrostatic repulsion between the molecules’ valence electrons around a central atom
• Bond angle is the angle between two bonds of a molecule and it is determined based on the electron-domain geometry.

  [Bond angles: tetrahedral = $\text{109}{\text{.5}}^{\text{o}}$, trigonal planar = ${\text{120}}^{\text{o}}$, T-shape = ${\text{90}}^{\text{o}}$]

• Sigma (σ) bonds: The bonds in which shared hybrid orbital’s electron density are concentrated along the internuclear axis and it is represented as the single bond between atoms in molecules.
• Pi (π) bonds: the bonds in which shared unhybridized orbital’s (p, d, etc) electron density are concentrated in above and below of the plane of the molecule.
• Double bonds: One sigma bond and one pi bond are together known as a double bond.

(b)

Interpretation Introduction

Interpretation:

The structures which are polar and the structures which are non-polar for the molecule $C_2{H}_{2}C{l}_2$ have to be given.

Concept introduction:

Two types of covalent bonds:

• Polar bond
• Nom-polar bond

Polar molecule: A molecule which has polar bonds and the dipoles did not cancel to zero.

Non-polar molecule: A molecule which has either non polar bonds or polar bonds whose dipoles cancel to zero.

(c)

Interpretation Introduction

Interpretation:

The energy in $kJ/mol$ involved has to be determined if the wavelength of approximately $200nm$ is required for isomerization.

Concept introduction:

Energy of the photon:

$\begin{array}{l}\text{E}\text{=}\frac{\text{hc}}{\text{λ}}\\ \text{h-Planck's}\text{constant}\\ \text{c-}\text{speed}\text{of}\text{the}\text{light}\\ \text{λ-}\text{wavelength}\end{array}$

(d)

Interpretation Introduction

Interpretation:

The orbitals involved in the central carbon-carbon bond and the reason for the high energy requirement for bond rotation in the molecule has to be given.

Concept introduction:

Hybrid orbitals:

The formation of four sigma bonds involves the $s{p}^3$ hybrid orbitals and when a carbon forms a double bond, $s{p}^2$ hybrid orbitals are involved.  When a carbon forms a triple bond, $sp$ hybrid orbitals are involved in bond formation.