Leif J. Saethre

Toxicity and chemical reactivity of naphthalene and methylnaphthalenes

Abstract Newly fertilized sea urchin and fish eggs were exposed to solutions of naphthalene and mono- and disubstituted methylnaphthalenes. The toxic effects were not dependent on the number of methyl groups alone, but rather on their specific ring positions. Comparison with calculated atom and bond reactivity indices indicates that the variation in toxicity is related to differences in electronic properties of the molecules. The results are in favour of an initial atom oriented interaction mechanism of toxicity.

Toxic effects of naphthalene and methylnaphthalenes on marine plankton organisms

Sea urchin eggs, fish eggs, and adult copepods showed different sensitivity towards aromatic hydrocarbons of the naphthalene type. Methylated naphthalenes were, however, more toxic than naphthalene. The toxicity was apparently not dependent on the number of methyl groups, but rather on their position on the naphthalene molecule. Ultrastructural studies of exposed sea urchin embryos did not reveal specific effects at the cellular level.

Effect of halogen substituents on carbon is ionization energies in haloethenes and haloethanes

Abstract Carbon 1 s ionization energies have been measured for ethene and ethane and for their monosubstituted halogen derivatives, CH 2 CHX and CH 3 CH 2 X (X = F, Cl, Br, I). The shift in ionization energies relative to the unsubstituted compounds is large for the carbon atoms directly attached to the halogen atom, but much less for the terminal carbon atoms. The effect of substitution is, however, remarkably similar for the two series of molecules. Ab initio calculations give results which are in good agreement with experiments and permit an analysis of the results in terms of initial-state potential energies and final-state relaxation energies. It is shown that the relative ability to accept charge at a carbon position is mainly determined by the initial-state potential and to a lesser extent by the relaxation energy. The effect of fluorine substitution on the initialstate potentials is almost exclusively confined to the directly bonded carbon, C1. The effect becomes less for C1 and is transmitted more to the terminal carbon C2 as the substituent is changed from fluorine to iodine, the combined effect being almost constant for both series of compounds. Molecular charge distributions have been calculated both for the initial state and for the coreionized state to aid interpretation. Results from integrated Bader populations on haloethenes show that the traditional point-charge model is inadequate to explain the shifts in initial-state potentials.

Gas phase ESCA studies of trithiapentalene and its 2,5-dimethyl derivative

Abstract 1,6,6a-trithiapentalene and its 2,5-dimethyl derivative have been studied in the gas phase by means of ESCA in order to elucidate the unusual type of SS bonding in these molecules. The high resolution spectra show very wide S 2p lines from the terminal sulfur atoms due to vibrational broadening. The effect of core ionization on the SS bond lengths in trithiapentalene has been estimated using the equivalent core approximation and the CNDO/2 method. Ground and final state potential curves have been calculated and explain qualitatively the differences in line widths for the terminal and central sulfur atoms. The observed chemical shifts agree with predictions from CNDO/2 and ab initio calculations.

Relativistic corrections to reported sulfur 1s ionization energies

Abstract Recently reported sulfur I s ionization energies are found to be systematically in error by about 0.5 eV, apparently because relativistic effects were not considered in the calibration of the spectrometer that was used for the measurements.

Molecular structure and photoelectron spectra of H2S, H2Se, and H2Te. Effective core potential calculations on ground and valence ionic states

Abstract Hartree—Fock effective core potential calculations have been performed for the neutral ground state ( 1 A 1 ) and the first three low-lying ionic states ( 2 B 1 , 2 A 1 and 2 B 2 ) of H 2 S, H 2 Se and H 2 Te. The computational method enabled us to use the same, relatively large, basis for all three molecules. The calculations include potential energy curves for the three ionic states, equilibrium geometries, vibrational frequencies, Franck—Condon factors, and ionization potentials. The results show satisfactory agreement between calculated and experimental values when comparison is possible, and indicate that molecules and ions containing heavy elements may be studied at a satisfactory level with the effective core potential method.

Formation of monoaldehydes by cerium(IV) ammonium nitrate oxidation of unsymmetric dimethylnaphthalenes

Abstract When 1,2-, 1,3-and 1,6 -dimethylnaphthalene are oxidized by Ce 4+ in acetic acid the corresponding monoaldehydes are formed in better than 80% yield. In each case aldehyde formation takes place with a high degree of selectivity as the methyl-1- to methyl-2-naphthaldehyde ratio is better than 11:1. The selectivity may be explained from differences in reactivity as calculated within the frontier orbital method.

Core-ionization energies and chemical properties

Abstract Core-ionization energies can be related to the charge distribution in molecules and to the ability of a molecule to accept charge at a particular location. Typically, charge distributions are discussed in terms of point charges centered on the nuclei of the atoms in a molecule. Once appropriate corrections for relaxation energies have been made, the core-ionization energies can be related to these point charges via potential models. However, the concept of an atomic charge in a molecule is not well defined. Baders method of integrating over basins of the charge distribution provides a method for defining such charges from the charge density, which is an observable quantity. Analysis of core-ionization energies in terms of Bader charges shows that the usual pointcharge model has serious drawbacks. Among these are that the charges on the atoms are not centered on the nuclei nor are they spherically distributed about the center of charge. Furthermore, the valence radius of an atom, which is taken to be constant in the point-charge model, depends significantly on both the atomic charge and the nature of the neighboring atoms. The point-charge model must, therefore, be replaced by one that includes the variability of the valence radius as well as the multipole nature of the charge distribution on the surrounding atoms. We find, however, that such a model even Including multipoles up to the octupole moment still does not give correct potentials and, hence, cannot provide an accurate picture of the effect of the charge distribution on the core-ionization energy. Core-ionization energies can be combined with gas-phase acidities, Auger kinetic energies, or results from ab initio calculations to show the influence of initial-state charge distribution and final-state relaxation on the ability of a molecule to accept charge at a specific location. Recent investigations of this nature have been concerned with the acidities of organic acids, such as carboxylic acids, phenol, and substituted phenols, with substituent effects in thiophene, and with factors that influence the rates of electrophilic addition. These have shown that traditional views about the effect of anionic resonance on acidities is incorrect. In addition, it is found that polarizable alkyl groups attached to electronegative centers affect the Initial-state potential as well as the final-state relaxation. For example, the higher acidity of formic acid relative to acetic acid arises because of this effect; the methyl group in acetic acid is more electron donating to the carbonyl carbon than is the hydrogen in formic acid. Investigations of substituted thiophenes show that there is significant resonance delocalization of electrons from the substituents to the ring in the neutral molecule and that the directing effect of the substituents is due to the initial-state charge distribution rather than delocalization of charge in the final state (or transition state). Relationships between experimental core-ionization energies and proton affinities (both experimental and theoretical) for fluoro-substituted ethenes illustrate the dominance of the initial-state potential over final-state relaxation in electrophilic addition reactions.

Effects of short-term exposure to xylenes on the early cleavage stages of cod eggs (Gadus morhua L.)

Abstract Seawater solutions of the three isomers of xylenes were analysed both by gas chromatography (GLC) and ultra-violet spectroscopy (UV), and the two methods were compared. Cod eggs were exposed to seawater solutions of the xylenes. Concentrations ranged from less than 1 ppm to c. 35 ppm. Treatment during fertilization with ortho-xylene had no significant effect upon fertilization capacity, while meta-and para-xylene induced significant decreases in fertilization rate at concentrations above 10 ppm (p < 0.05). Fertilized cod eggs were exposed to xylenes 3 or 6 hours before the first cleavage. There was no significant difference in effect between the xylenes, and treatment for 3 and 6 hours gave similar effects. Effects upon the early cleavage pattern were significant from a concentration interval of 2–7 ppm (p < 0.01). Characteristic effects included inhibition of the formation, of the cleavage furrow. ‘Small cells’ or total absence of cleavage occurred in the highest concentrations (16–35 ppm), whil...

Accurate calculation of brønsted acidities using low-level ab initio methods

Gas-phase acidities calculated at three different levels of ab initio theory are presented. At the MP4/6-311 + +G (2d,p) level the calculated acidities for methane, methanol, and formic acid, corrected for zero-point energy temperature, are within 3 kcal mol−1 of the experimental values of ΔH°298. At the RHF/3-21 + G//3-21 + G level the calculated acidities of 12 compounds deviate systematically from the experimental values. However, there is a good linear correlation between the theoretical experimental acidities. This correlation can be used together with acidities calculated at this level to provide predictions of acidities that are probably within 3 kcal mol−1 of the correct values. Acidities for the same compounds calculated at the RHF/STO-3G// STO-3G level scatter about the correlation line, and the reliability of predicted acidities based on such calculations cannot be expected to be better than about 12 kcal mol−1. Acidities calculated at the same level for a series of substituted phenols, however, correlate well with the experimental values.