Chapter 8, Problem 1Q

Interpretation Introduction

(a)

Interpretation:

The computional chemistry method from MM or QM used to compare the heat of formation of isomeric structures needs to be determined.

Concept Introduction:

The branch of chemistry uses result of theoretical chemistry incorportaed into efficient computer programmed in order to calculate properties and structure of the molecule is said to be computational chemistry.

Answer to Problem 1Q

QM or quantum mechanics method.

Explanation of Solution

The quantum mechanics method is based on the solution of the Schrodinger wave equation which is represented as follows:

  $\widehat{H}\psi =E\psi$

Here, $\widehat{H}$ is the Hamiltonian operator that describes the kinetic energies and the electrostatic forces of interactions between the nucleus and electrons. Also $E$ is the energy of the system and $\psi$ is wavefunction. The following assumptions are made during the calculation of the wave equation.

1. The nucleus is assumed to be stationary with respect to the electron.
2. The movement of electrons is independent of each other. The single electron can affect the average electric field due to its motion.
3. The molecular orbital is made by a linear combination of the atomic orbitals.

The molecular mechanics method is used to compare the energies of conformers but not for the isomeric compounds which are not conformers. The method is not reliable for comparison of the energies of isomers but this can be well explained by the quantum mechanical methods.

Thus, QM or quantum mechanics method is used to compare the heat of formation of isomeric structures.

Interpretation Introduction

(b)

Interpretation:

The computional chemistry method from MM or QM used to determine the difference in energy between the diaxial and diequitorial cis-1,3-dimethylcyclohexane needs to be determined.

Concept Introduction:

The branch of chemistry uses result of theoretical chemistry incorportaed into efficient computer programmed in order to calculate properties and structure of the molecule is said to be computational chemistry.

Answer to Problem 1Q

MM or molecular mechanics.

Explanation of Solution

The best computational method can be determined by analyzing the question. If the optimum or lowest energy structure of organic molecules needs to be determined, it can be best determined by using molecular mechanics. The exact value of bond angles, bond lengths and interatomic distances can be determined using this method. A molecular mechanics method can be used to calculate the values more efficiently.

Thus, the difference in energy between the diaxial and diequitorial cis-1,3-dimethylcyclohexane is determine by MM or molecular mechanics method.

Interpretation Introduction

(c)

Interpretation:

The computional chemistry method from MM or QM used to determine the highest occupied molecular orbital needs to be determined.

Concept Introduction:

The branch of chemistry uses result of theoretical chemistry incorportaed into efficient computer programmed in order to calculate properties and structure of the molecule is said to be computational chemistry.

Answer to Problem 1Q

QM or quantum mechanics method.

Explanation of Solution

The electronic behavior of atoms and molecules can be described by quantum mechanical methods. On the other hand, the molecular mechanics is used to calculate the bond formation and bond dissociation energies. The highest molecualr orbital can be determined by studying the electronic behavior thus, QM or quantum mechanics method is used here.

Interpretation Introduction

(d)

Interpretation:

The computional chemistry method from MM or QM used to determine the charge distribution of the intermediate of reaction needs to be determined.

Concept Introduction:

The branch of chemistry uses result of theoretical chemistry incorportaed into efficient computer programmed in order to calculate properties and structure of the molecule is said to be computational chemistry.

Answer to Problem 1Q

MM or molecular mechanics method.

Explanation of Solution

In the molecular mechanics method, the molecule is treated as made up of balls (atoms) and springs (bonds). Here, springs connects the balls. The total energy of molecule is known as strain energy and it is sum of the energy contributed due to stetching, strain in anghle and electronic charge interactions.

Molecular mechanics method can be used in the study of large systems like trans membtrane proteins. It cannot be used to simulate the chemical reactions as, it cannot handle breaking and formation of the chemical bonds. Thus, the charge distribution of the intermediate of reaction is measured by MM or molecular mechanics method.

Interpretation Introduction

(e)

Interpretation:

The computional chemistry method from MM or QM used to determine the lowest energy conformation of cyclodecane needs to be determined.

Concept Introduction:

The branch of chemistry uses result of theoretical chemistry incorportaed into efficient computer programmed in order to calculate properties and structure of the molecule is said to be computational chemistry.

Answer to Problem 1Q

MM or molecular mechanics method.

Explanation of Solution

In the molecular mechanics method, the molecule is treated as made up of balls (atoms) and springs (bonds). Here, springs connects the balls. The total energy of molecule is known as strain energy and it is sum of the energy contributed due to stetching, strain in angle and electronic charge interactions. Thus, the lowest energy conformation of cyclodecane can be determined using the MM or molecular mechanics method.