The Molecular Structure of Allenes and Ketenes, IX [1] π and σ Interactions in Allenes: Photoelectron Spectra, Electronic Absorption Spectra, and Quantum‐Chemical Calculations

Abstract

The electronic structure of monosubstituted allenes has been investigated by means of photoelectron and UV absorption spectroscopy.—The assignment of the photoelectron and UV absorption bands is achieved on the basis of a “composite molecule” (LCMO) model and substantiated by comparisons with structurally related molecules.—Assuming the validity of Koopmans' approximation for the interpretation of photoelectron spectra the π electronic structure of allenes can be rationalized quantitatively in terms of a three‐parameter model of substituent effects which involves short‐range and long‐range inductive effects and resonance effects.—The substituent effect on the highest‐occupied σ orbital of allenes is shown to be essentially an electrostatic (long‐range) field effect. The interpretation of low‐energy 1A” excited states of allenes is achieved via a correlation of UV spectroscopic and photoelectron spectroscopic data.—The interpretation of experimental results is corroborated and refined by semiempirical (CNDO/S) and ab initio (STO‐3G and STO‐4.31G) calculations.—In general, there are analogies of the molecular properties of allenes with those of ethylenes and benzenederivatives and with those of carbonylcompounds and acetylenes.

Density Functional Exploration of C4H3N Isomers

“…Calculations in 1994 at the HF/6-31G* level gave the enthalpy of the isodesmic reaction converting 2 to 8 , as well as the energy difference between 2 and 6 , along with selected vibrational frequencies . A number of calculations of excited states have been made in support of photoelectron spectroscopy studies to determine ionization potentials. − Work from 2009 has also included calculations at the RCCSD­(T)/aug-cc-pVTZ level which give electric dipole moments, polarizabilities, bond distances, and selected bond angles for the most stable C 4 H 3 N family members: 1 , 2 , and 3 . IR frequencies and rotational constants have been reported at the B3LYP/aug-cc-pVTZ level for species 2 and 3 .…”

“…Calculations in 1994 at the HF/6-31G* level gave the enthalpy of the isodesmic reaction converting 2 to 8, as well as the energy difference between 2 and 6, along with selected vibrational frequencies 27 . A number of calculations of excited states have been made in support of photoelectron spectroscopy studies todetermine ionization potentials[28][29][30][31][32] . Recent work has also included calculations at the…”