Huckel MO Theory Research Articles

Electronic absorption spectroscopy of some exceptionally stable 1,4-dialkyl-1,4-dihydro-1,4-diazinium radical cations: assignment of transitions, vibrational structure and effects of π–π dimerization

UV–VIS Absorption spectroscopy of the unusually stable and structurally characterized radical cations 1,4-diethyl-1,4-dihydropyrazinium (1˙+), 1,4-diethyl-1,4-dihydroquinoxalinium monomer (2˙+) and π–π dimer [(2˙+)2], 1,4,6,7-tetramethyl-1,4-dihydroquinoxalinium (3˙+) and 5,10-diethyl-5,10-dihydrophenazinium (4˙+) reveals low-energy π→π* transitions with different intensities and partial vibrational structuring. The spectra of the radical cations and of the corresponding dications (12+–42+) have been analysed with the help of INDO/S calculations; the resulting assignments could also be rationalized using Huckel MO theory. Both higher symmetric systems 1˙+ and 4˙+ exhibit vibrationally split long-wavelength bands. The additional long-wavelength absorption of the π–π dimer (2˙+)2(KDca. 4 × 103) is assigned to a charge transfer transition, similar to that of methylviologen radical dimer.

Huckel MO theory and electron spin resonance in the spectroscopy course

83. Bits and pieces, 34. A computer program that does Huckel MO calculations and allows the calculation of energy levels, MO coefficients, bond orders, and electron densities; another the simulates ESR spectra on the computer.

Generation of the eigenvectors of the topological matrix from graph theory

The technique of describing the characteristic polynomial of a graph is here extended to construction of the eigenvectors. Recurrence relations and path tracing are combined to generate eigenvector coefficients as polynomial functions of the eigenvalues. The polynomials are expressed as linear functions of Chebyshev polynomials in order to simplify the computational effort. Particular applications to the Huckel MO theory, including heteroatom effects, are shown.

An extended Hückel study of hydrogen and oxygen chemisorption on Ru(001) surface

Abstract Extended Huckel MO theory has been applied to treat the chemisorption of hydrogen and oxygen atoms on Ru(001) surfaces. The site of chemisorption, surface-adatom distance, chemisorption energy and the vibrational frequency of the adatom on the surface have been calculated. For different sites, the chemisorption energy ( E c ) results are as follows: For hydrogen, | E c |(centre) > | E c |(top) > | E c |(bridge); while for oxygen, | E c |(bridge) > | E c |(top) > | E c |(centre). These results are critically discussed in the light of the recent results obtained from the electron energy-loss spectroscopy (EELS) experiments.

Computerized visual aids in introductory MO theory

A computer program in Basic has been developed to facilitate student use of Huckel 's MO theory.

On the correlation between the carbonyl vibrational frequency of substituted thenoyl chlorides and the rate of their reaction with aniline

An interpretation is proposed for the observed linear correlation between the carbonyl i.r. of 3- and 5-substituted thenoyl chlorides and the logarithm of the rate constant of their reaction with aniline. Simple Huckel MO theory, both in its complete form and in its perturbation approximation, shows that the substituent effect on the π-electron population of the carbon atom of the CO group is linearly related to the substituent effect on the reaction rate. The activation energy of the reaction has been evaluated from the HMOs of the separate molecules by fitting them into a supermolecule scheme. The bond formed in the activated state was treated as a charge transfer from the HOMO of aniline to the LEMO of the substituted thenoyl chlorides. This model accounts for the observed correlation between the substituent effect on the reaction rate and that on the ν(CO) absorption band. The complete HMO treatment gives a better agreement than the perturbation approach. The following suggestions are made. (i) A similar correlation is expected for the substituent effect in furan- and pyrrole-2-carbonyl chlorides. (ii) A search should be made for a charge-transfer absorption band in the spectra of the reacting molecules.

Photochemistry and a model for adsorption of some conjugated hydrocarbons

Adsorption and photochemical reactions of some phenyl-substituted conjugated molecules have been studied on a commercial Al2O3 adsorbent. The heats of adsorption are correlated with the number of conjugated double bonds. Steric effects are discussed. Photocyclization and photooxidation are observed. From this experimental material a model for adapting Huckel MO-theory to the adsorption process is derived. This model, used with 2nd order HMO perturbation theory gives encouraging results on photo-chemical reactivity of adsorbed conjugated molecules.

ChemInform Abstract: AN MO‐THEORETICAL INTERPRETATION OF THE REDUCTIVE CLEAVAGE OF ORGANIC HALIDES BY PENTACYANOCOBALTATE(II)

Chemischer InformationsdienstVolume 4, Issue 52 Preparative Organic Chemistry ChemInform Abstract: AN MO-THEORETICAL INTERPRETATION OF THE REDUCTIVE CLEAVAGE OF ORGANIC HALIDES BY PENTACYANOCOBALTATE(II) KATSUTOSHI OHKUBO, Search for more papers by this authorHIROKAZU KANAEDA, Search for more papers by this authorKOHJI TSUCHIHASHI, Search for more papers by this author KATSUTOSHI OHKUBO, Search for more papers by this authorHIROKAZU KANAEDA, Search for more papers by this authorKOHJI TSUCHIHASHI, Search for more papers by this author First published: December 25, 1973 https://doi.org/10.1002/chin.197352167Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue52December 25, 1973 RelatedInformation

Relative validity of the valence bond theory and of the molecular orbital theory for description of conjugated hydrocarbons

It is shown that MO theory predicts the butadiene molecule to be flat, and that VB theory predicts a skewed configuration of this molecule. The calculations of the resonance energy of conjugated systems, using either VB or MO theory, are discussed and compared. Benzede is taken as an example. Emphasis is laid on the requirement of similarity between the theoretical calculation and the empirical determination of the resonance energy. Using simple Huckel MO theory, the resonance energy of benzene is then predicted with the correct sign and in the right order of magnitude. However, with valence bond theory one finds the wrong sign for the resonance energy of benzene. The cause of this failure of valence bond theory is discussed. It is concluded that description of conjugated systems by the MO theory is far superior. © 1966 Taylor and Francis Group, LLC.