Electronic Spectra of Isoelectronic Amides, Acids, and Acyl Fluorides

The first four bands in the gas‐phase spectra of amides, carboxylic acids, and acyl fluorides are thought to be $\mathrm{n\hspace{0.17em}\to \hspace{0.17em}\pi *}$ , $\text{n\hspace{0.17em}→\hspace{0.17em}3s}$ Rydberg, $\mathrm{\pi \hspace{0.17em}\to \hspace{0.17em}\pi *}$ , and $\text{n\hspace{0.17em}→\hspace{0.17em}3p}$ Rydberg excitations. That the second and fourth bands are Rydberg, whereas the first and third are valence shell is demonstrated in a comparison of gas‐phase and condensed‐phase absorption and circular dichroism spectra. All‐electron, SCF Gaussian orbital calculations are also presented which qualitatively explain the trends in the spectra of HCOX molecules, and predict several quantities of interest, such as upper‐state dipole moments and magnetic transition moments, which have not been measured as yet.