INDO Molecular Orbital Calculations Research Articles

Identity of the Radicals Observed by ESR in Aqueous Solutions of Uracil during Fast Electron Irradiation

Aqueous solutions of uracil have been studied during their irradiation with fast electrons. This subject was first reported on by P. Neta in a series of papers which appeared in 1972 and 1973. Similar spectra, which are clearly due to the same radical species, are reported here. Unlike the previous work, however, attempts are made to identify the radicals responsible for the spectra with the help of INDO and CNDO molecular orbital calculations. These calculations support the suggestion that the radicals observed in aqueous solutions of uracil are produced by OH attack at C(5) leading to a radical having a keto group at this point. They do not support, however, the suggested ring opening at pH 11 to 12.5 and suggest instead that the radical formed is of sigma type.

Microwave Spectrum, Dipole Moment and Centrifugal Distortion Constants of 1,2,4-Trifluorobenzene

The microwave spectrum of 1,2,4-trifluorobenzene has been studied at dry ice temperature in the frequency region of 8 to 12.4 GHz. The molecule exhibits a very dense spectra of both a- and b-type. The analysis of 59 selected transitions from a large number of measured lines yields the following spectroscopic constants of the molecule for Watson's reduced Hamiltonian in the I r representation: A =3084.0215±0.0062 MHz, B =1278.3595±0.0027 MHz, C =903.6835±0.0027 MHz, Δ J =-0.0674±0.0054 kHz, Δ J K =0.728±0.052 kHz, Δ K =-0.657±0.016 kHz, δ J =0.0528±0.0032 kHz and δ K =-0.574=0.059 kHz. The dipole moment of the molecule has been determined as 1.39±0.03 D. The INDO and CNDO molecular orbital calculations give the value of the dipole moment as 1.77 D and 1.63 D respectively. The benzene ring appears to have undergone a distortion, if the C(sp 2 )–F bond length is assumed to be 135 pm.

Correlation of the reactivity of coordinated π-hydrocarbons with electronic parameters : III. Stabilization of the benzyl cation coordinated to Cr(CO) 3

INDO molecular orbital calculations have been carried out on the free benzyl carbonium ion and on the coordinated cation [(benzyI)Cr(CO) 3] +. The remarkable stability of the coordinated benzyl cation is shown to arise via backbonding from the chromium d x 2− y 2 orbital into the non-bonding π-orbital of the benzyl ligand. This model is discussed in relation to previous proposals for the mode of stabilization.

Vibronic effects on the hyperfine splitting constants of pyridinyl radicals

The aN and aIINH hyperfine splitting constants of pyridinyl are poorly reproduced by INDO molecular orbital calculations if assuming a planar geometry for the radical. A much better agreement with experiment has been found by evaluating these constants from vibronic wavefunctions even though at a semiquantitative level. The effects of substituents and of solvent polarity on the hyperfine splittings of pyridinyls are also discussed.

Ab initio and indo molecular orbital calculations of the geometries and electronic structures of substituted sulfines

Ab initio and indo molecular orbital calculations of the geometries and electronic structures of substituted sulfines

Ab initio and indo molecular orbital calculations of the geometries and electronic structures of substituted sulfines

Molecular orbital calculations are presented for the parent sulfine and some mono-and dihalogensubstituted sulfines, using ab initio and INDO methods. A partial geometry optimization was performed for nine different sulfines. Charge distributions, potential surfaces and dipole moments were calculated from the wave functions of the optimized geometries. Cis-trans interconversion barriers and electronic spectra are also given. The atomic charges of the S and O atoms are insensitive to substitutions at carbon, and substituents greatly influence the potential in the environment of the molecule. The implications of the results for the chemical behavior of sulfine derivates are briefly discussed and compared with experimental data.

UV photoelectron studies of biological pyrimidines: the valence electronic structure of methyl substituted uracils

UV photoelectron spectroscopy and INDO molecular orbital calculations have been employed to investigate the electronic structure of several methyl substituted uracils. The results indicate that the ionization potential of uracils is most sensitive to perturbation at the 1 and 5 positions. Substitution occurs in both of these positions in biological systems. It is also found that the large (0.4 eV) differences in the ionization potential of uracil and thymine is conserved in the nucleoside models 1-methyluracil and 1-methylthymine.

ChemInform Abstract: PARAMAGNETIC RESONANCE STUDY OF PHOTOLYZED CRYSTALS OF DIMETHYLNITRAMINE

Chemischer InformationsdienstVolume 7, Issue 18 Physical Organic Chemistry ChemInform Abstract: PARAMAGNETIC RESONANCE STUDY OF PHOTOLYZED CRYSTALS OF DIMETHYLNITRAMINE F. J. OWENS, F. J. OWENSSearch for more papers by this authorVERONICA L. VOGEL, VERONICA L. VOGELSearch for more papers by this author F. J. OWENS, F. J. OWENSSearch for more papers by this authorVERONICA L. VOGEL, VERONICA L. VOGELSearch for more papers by this author First published: May 4, 1976 https://doi.org/10.1002/chin.197618053AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue18May 4, 1976 RelatedInformation

Structural studies on some 1,3,5,7‐tetraaza‐ and 1,3,5‐triazaadamantane derivatives

Abstract1H and 13C NMR data are reported for hexamethylenetetramine (hexamine), 7‐nitro‐1,3,5‐triazaadamantane and some of their quaternary derivatives. INDO molecular orbital calculations have been performed on these molecules to aid the interpretation of their spectra.

Paramagnetic resonance study of photolyzed crystals of dimethylnitramine

The uv-irradiation of single crystals of dimethylnitramine, (CH3)2–N–NO2, produces an EPR spectrum arising from an unpaired electron with hyperfine coupling to six hydrogen and one nitrogen nuclei. The parameters of the axial spin Hamiltonian are g∥=2.0017, g⊥=2.0091, A∥(N) =33.0 G, A⊥(N) =6.5 G, and Aiso(H) =14.0 G. The spectrum is assigned to a (CH3)2–N radical. INDO molecular orbital calculations of hyperfine splittings in the (CH3)2–N radical support the assignment when allowance is made for the strong dependence of the hydrogen isotropic hyperfine splitting on the C–N bond length.

Tautomerism of histamine

Both ab initio and INDO molecular orbital calculations on histamine show that the histamine N(3)H tautomer is preferred for the monocationic form, whereas in the neutral state the N(1)H tautomer is favored. This implies that upon neutralization of the protonated histamine which is predominant in the neutral aqueous solution the tautomeric shift occurs from the N(3)H to the N(1)H form. Although the total electronic energy term makes the N(1)H tautomer of the monocation more favorable, it is the nuclear repulsion term that results in the N(3)H tautomer for the monocation being more stable. The tautomeric energy difference for both the neutral and protonated histamines is independent of the side chain conformations.

The chemical dynamics of base adducts with bis(N,N-dithiocarbamate)nickel(II)

The chemical dynamics for the adduct reactions of the nitrogen bases pyridine, 2-picoline, 3-picoline, 4-picoline and 3,5-lutidine with bis(N,N-dialkyldithiocarbamate)nickel(II) were investigated. The thermodynamic parameters for adduct formation were determined by NMR techniques. The pyridine-Ni(diR,R′dtc) 2 adducts have the stability order -CH 2H 5 < -n-C 3H 7 < -n-C 4H 9; the order is controlled by entropy rather than by enthalpy effects contrary to previously reported results from i.r. and vis spectral studies. At low temperatures the adduct stability order of Ni-(din-butyldtc) 2 with pyridine type bases is 3,5-lutidine < 3-picoline < 4-picoline < pyridine. However, at 25°C the order changes to pyridine ∼3-picoline ∼3,5-lutidine < 4-picoline, the change in stability order with temperature being attributed to the T Δ S° term. The kinetic parameters ΔH ≠, and ΔS ≠ for 3-picoline and 4-picoline exchange with Ni(din-butyldtc) 2 were determined by NMR line broadening techniques. The rate constants, κ ≠, were found to be 12·5 × 10 4 sec −1 for 3-picoline and 6·2 × 10 4 sec −1 for 4-picoline. Temperature studies of contact shifts and INDO molecular orbital calculations are used to analyze the unpaired spin density transfer between the Ni(din-butyldtc) 2 and the pyridine type bases.

Nitrogen NMR chemical shifts of some simple azines interpreted by INDO molecular orbital calculations

The average excitation energy approximation, used in conjunction with INDO molecular orbital calculations, is shown to give a quantitative correlation between the experimental nitrogen chemical shifts of some azine ring systems and the calculated values of the local paramagnetic term. The molecules studied include pyridine, three isomeric diazines, 1,3,5-triazine, and 1,2,4,5-tetrazine. The results obtained compare favorably with previous estimates of the nitrogen nuclear screening in these molecules.

Uv photoelectron studies of biological pyrimidines: The electronic structure of uracil

The photoelectron spectrum of uracil has been measured in the gas phase. A qualitative interpretation of the spectrum indicates that the first and third highest occupied orbitals in uracil are π orbitals, while the second and fourth highest orbitals are lone-pair orbitals associated with oxygen atoms. This ordering is consistent with that predicted by CNDO and INDO molecular orbital calculations.

An Investigation of σ and π Contributions to Long-range 1H–1H Coupling Constants in Planar Aromatic Derivatives Using CNDO and INDO Molecular Orbital Calculations

Molecular orbital calculations of coupling constants based on finite perturbation theory in the CNDO/2 and INDO approximations have been carried out for styrene, benzaldehyde, and naphthalene. INDO calculations have also been carried out in which one-center exchange integrals involved in σ–π interaction are omitted (INDO(σ) calculations). Both CNDO and INDO(σ) constants give reasonable estimates of σ contributions to long-range 1H–1H couplings, with the former giving better results when strongly stereospecific σ contributions are present. INDO calculations also give reasonable, but generally overestimated, π contributions to these couplings.

Nuclear magnetic resonance contact shifts and spin delocalization mechanisms in tris(acetylacetone) nickel(II) perchlorate

The NMR contact shifts for the complex tris(acetylacetone) Ni(II) perchlorate have been found to be +4.7 ppm for the methyl group and +35.6 for the methylene group. INDO molecular orbital calculations are used to show that the major spin delocalization is into the highest filled ligand orbital which is of sigma symmetry, with a minor contribution from delocalization into the lowest empty pi orbital. In the case of Ni(acac) 3 − and Ni(acac) 2(py) 2 the major spin delocalization is into the highest filled ligand orbital, of π symmetry, with a minor contribution from the next highest filled orbital, which is a sigma type. For Co(acac) 2(py) 2 an additional mechanism, which places spin in the third highest filled orbital, also sigma, is found to be consistent with the contact shift results. The implications of these results on the “ratio method” of separating contact and dipolar shifts in complexes of the type M(acac) 2L 2, M  Co, Ni, is discussed and the donor properties of the acetylacetone and acetylacetonate ligands are compared.

The ortho effect in mass spectra. Insight into the tightening of activated complexes for the loss of ketene from phenyl acetates and ethylene from phenetoles from INDO molecular orbital calculations

AbstractINDO Molecular orbital calculations of the energetically most favourable conformation of the molecular ions of phenyl acetate and its o‐fluoro‐ and o‐chloro‐analogs indicate bond formation between carbonyl oxygen and ortho halogen. For the molecular ions of phenetole and its o‐fluoro and o‐chloro‐analogs, no ring formation is observed. These results are in accord with the frequency factor changes found for the ortho substitution in these systems by halogens.

An Investigation into σ and π Contributions to Long Range 1H–1H Coupling Constants in Conjugated Dienes and Diynes Using CNDO and INDO Molecular Orbital Calculations

Molecular orbital calculations based on finite perturbation theory in the CNDO/2 and INDO approximations are carried out for fourteen conjugated dienes and diynes for which experimental results are available. There is generally very good agreement between experimental and calculated (INDO) coupling constants. Comparison of results of CNDO/2 and INDO calculations elucidates the relative importance of σ and π pathways for the various long-range coupling constants.

ChemInform Abstract: INDO MOLECULAR ORBITAL CALCULATIONS OF THE DIPOLE MOMENT AND CONFORMATION OF METHYL FORMATE AND METHYL FLUOROFORMATE

Chemischer InformationsdienstVolume 4, Issue 34 Physical Organic Chemistry ChemInform Abstract: INDO MOLECULAR ORBITAL CALCULATIONS OF THE DIPOLE MOMENT AND CONFORMATION OF METHYL FORMATE AND METHYL FLUOROFORMATE E. BOCK, E. BOCKSearch for more papers by this authorE. TOMCHUK, E. TOMCHUKSearch for more papers by this author E. BOCK, E. BOCKSearch for more papers by this authorE. TOMCHUK, E. TOMCHUKSearch for more papers by this author First published: August 21, 1973 https://doi.org/10.1002/chin.197334079AboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue34August 21, 1973 RelatedInformation

INDO Molecular Orbital Calculations of the Dipole Moment and Conformation of Methyl Formate and Methyl Fluoroformate

AbstractThe electric dipole moment and the total molecular energy of methyl formate and methyl fluoroformate for different molecular conformations was calculated using the INDO molecular orbital approximation. It was found that the calculated dipole moments were in fair agreement with the experimentally measured dipole moments. It was also found that the most stable molecular conformations predicted by INDO calculations were in agreement with the experimentally determined conformations.