Chapter D, Problem D.9YT

Interpretation Introduction

Interpretation:

The atomic orbital overlap and MO energy diagrams for ${\text{CH}}_{\text{3}}\text{COCl}$ (Figs. 3-13 through 3-25 to be reviewed) are to be constructed and these diagrams are to be used to determine its LUMO. Whether the answer agrees with the one shown in Figure D-8a is to be explained.

Concept introduction:

Molecular orbitals are constructed from the AOs of different atoms. When two atoms are brought close enough together (i.e., about a bond length apart), the AOs of one atom significantly overlap the AOs of the other atom, enabling them to undergo constructive and destructive interference, or mix, to produce new orbitals. The central $\text{C}$ and $\text{O}$ atoms are both ${\text{sp}}^{\text{2}}$ hybridized in ${\text{CH}}_{\text{3}}\text{COCl}$, and each has an unhybridized pure p-orbital. The $\text{C}$ atom of the ${\text{CH}}_{\text{3}}$ and the Cl atom are both ${\text{sp}}^{\text{3}}$ hybridized, and each $\text{H}$ atom contributes a 1s orbital. End-on overlap occurs in the $\text{C-H}$ and $\text{C-C}$, $\text{C-Cl}$, and $\text{C-O}$ bonding and, therefore, results in six $\text{σ}$ bonds. Side-by-side overlap occurs between the two pure p orbitals of $\text{C}$ and $\text{O}$. This results in a $\text{π}$ bond. When the $\text{14}$ AOs overlap, $\text{14}$ MOs are produced: six $\text{σ}$, six ${\text{σ}}^{\text{*}}$, one $\text{π}$ bonding, and one ${\text{π}}^{\text{*}}$ antibonding.

(LCAOs).