The structuredness of solvents. 2. Data for ambient conditions

In view of the inadequacy of Trouton's constant for the expression of the structuredness of solvents at ambient temperatures, alternative measures have been sought. Calculations of the entropy deficit _vapS⁰/R of solvents at ambient conditions relative to their vapors and compared to presumably unstructured alkanes with the same number and arrangement of skeletal atoms have been made. Data for nonpolar, dipolar aprotic, non-hydroxylic protic and hydroxylic solvents are presented, with _vapS⁰/R>2 representing structured solvents. Empirically, the heat capacity density of solvents at ambient temperatures, [C _p (l)-C _p (g)]/V], is another meaningful measure of the structuredness of solvents, compatible with the former one. Values>0.6 J-K^–1-cm^–3 signify a structured solvent.     

The search for new biochemical photoprobes. II. The nucleophilic photosubstitution of 2-fluoro-4-nitroanisole.

The photosubstitutions of 2-fluoro-4-nitroanisole with several amines are studied. The preparative results, the thermal stability of the photochemical substrate, and the limiting quantum yield values obtained from photoreactions with several nucleophiles suggest the possible usefulness of 2-fluoro-4-nitrophenyl ethers as biochemical photoprobes.     

The A. J. P. Martin award recipients for 1988

The A. J. P. Martin award recipients for 1988     

The C. S. Jubilee medal recipient for 1988

The C. S. Jubilee medal recipient for 1988     

The Cyclopropylcarbinyl-Cyclobutyl-Homoallylic Rearrangement. Part III. Evidence for a symmetrical intermediate and for two discrete rearrangement processes

In buffered 70% aqueous dioxane the cyclopropylcarbinyl ( 1 -X), endo-cyclobutyl ( 2 -X) and homoallylic ( 3 -X) derivatives (X = nucleofuge) react to give the same mixture of alcohols 1 -OH and 3 -OH by way of a common intermediate, the symmetrical homoallylic ion 22 . This follows from a study of optically active reactants 1 -X and 3 -X and from the deuterium scrambling pattern in the products from deuteriated 1 -X, endo- 2 -X and 3 -X. The high solvolysis rates of 3 -X indicated π-bond participation in the transition state, while the high rates of 1 -X and endo- 2 -X reflect strong σ-bond participation which is absent in exo- 2 -X. Prolonged heating of 1 -X, endo- 2 -X and 3 -X in formic acid leads to a degenerate rearrangement of the initially formed 3 -formate. As evidenced by deuterium scrambling, carbon atoms 1, 3 and 7 eventually become positionally equivalent in the latter compound.     

Structure and Chemistry of Malonylmethyl- and Succinyl-Radicals. The search for homolytic 1,2-rearrangements

Malonylmethyl radical I [· CH₂CH(COOEt)₂] and its thioester analogue II [· CH₂CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and II were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2-shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals III and IV , respectively, was found at temperatures below ? 40°C. At higher temperatures of up to 140°C, the search for malonylmethyl → succinyl rearrangement was examined by thorough-product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to III by photolysis and of the radical II to IV by thermolysis at 130°C in chlorobenzene to only a small extent.     

The Fundamental Basis for Cyclopolymerization. III. A Spectroscopic Study of Dimethacrylamides

The purpose of this investigation was to prepare suitable solid 1,6-dienes and the corresponding monoenes and to compare their UV and NMR spectra. A comparison of their polymerization characteristics will be reported in the succeeding paper of this series. The compounds chosen for this study were dimethacrylamide, N-isobutyrylmethacrylamide, and their N-methyl and N-phenyl derivatives. Since the dimethacryl derivatives are solids at room temperature, they are suitable monomers for solid-state polymerization studies, the results of which could lead to significant conclusions regarding the fundamental basis for cyclopolymerization. A previously postulated electronic interaction between the neighboring double bonds of the dienes should be detectable when their UV spectra are compared with their monoene counterparts. The UV spectra of the N-isobutyrylmethacrylamides and dimethacrylamides were compared with the spectra of the related di-isobutyramides, methacrylamides, and isobutyramides. The spectra of the diacylamides were much more complicated than predicted, and it seems that interaction of the carbonyls through the nitrogen is the major factor affecting the observed spectral transitions. This is different from the corresponding anhydrides in which the carbonyl groups appear to behave as isolated chromophores. The NMR spectra of the compounds were determined since a comparison of chemical shifts and variations of chemical     

Rate constants for radical recombination. III. The trifluoromethyl radical

Products of the radical reactions arising from t-Bu₂O₂, CF₃I, and CH₃I at 146°C in the vapor phase have been measured over a 33-fold range of CH₃I/CH₃I ratios and shown to be governed by the rapidly established equilibrium Together with K estimated by thermochemical methods, the results yield, for the rate of recombination for CF₃· radicals, k_r = 10^{9.7 ± 0.5} M^?1 sec^?1.     

Scaling factors for the prediction of vibrational spectra. II. The aniline molecule and several derivatives

The structure of aniline was studied by semiempirical, ab initio, and density functional methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational frequencies of aniline was determined. The normal modes were characterized by the magnitudes and direction of the displacement vectors. Three procedures were used to obtain the scaled frequencies, two of them new, using specific scale factors and scaling equations from the benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost‐effective method and procedure of scaling was carried out. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Thermodynamics and relaxation. The relationship between memory for past history and equilibrium

Thermodynamic theory is traditionally developed without any consideration of time. This procedure has been successful for materials and phenomena which have either exceedingly long or exceedingly short relaxation times. Polymers have typically relaxation times comparable to the time scale of actual experiments, and a basically new approach to thermodynamic theory is thus required. p]The modern mathematical theory of relaxation thermodynamics is briefly reviewed, and its application to polymers is discussed. Particular emphasis is placed on the need for an appropriate definition of equilibrium. Connections with polymer physics are briefly discussed.     

II. The case for the Big Bang

I describe the evidence for the Big Bang, including the various cosmological parameters. There is general concordance on their values, although the uncertainties remain large enough to justify the ensuing debate. Structure formation is reviewed, and here there is consensus on the hierarchical nature of the sequence of formation. The cosmic microwave background anisotropies provide a glimpse of the initial conditions that seeded structure, and the evolution of clouds of dark matter is an inevitable consequence. There are two outstanding mysteries: the very beginning where a theory of quantum gravity is eagerly awaited, and the detialed nature of galaxy formation, where observations are well ahead of theory.     

The NMR spectra of the carbanions of xanthene and thioxanthene. Evidence for paratropism

The proton NMR spectra of the carbanions of xanthene [XH]^? and thioxanthene [TxH]^? have been recorded and interpreted. Paratropism in the central rings of [XH]^? and [TxH]^? is inferred from a comparison of the chemical shifts with those of the carbanion of 9,10-dihydroanthracene [AH]^?. The contributions to the chemical shifts arising from n-electron excess charges, local dipoles and magnetic anisotropies are discussed. Numerical values for the various ring currents have been estimated by a least squares analysis of the observed chemical shifts after applying corrections for the excess charge effect. The results point to a strongly increasing paramagnetic ring current in the central ring in the order [AH]^?, [TxH]^?, [XH]^?.     

Breakdown of the pseudopotential approximation for magnetizabilities and electric multipole moments. II. The importance of gauge invariance for large-core semi-local pseudopotentials

In a previous paper we pointed out that core contributions to the static magnetizability are non-negligible, and can therefore lead to erroneous results within the pseudopotential approximation [P. Schwerdtfeger, B. Assadollahzadeh, U. Rohrmann, R. Scha?fer, and J. R. Cheeseman, J. Chem. Phys. 134, 204102 (2011)]. In a recent paper van Wu?llen showed that additional terms arising from the gauge-invariant condition for the semi-local part of a pseudopotential operator can lead to non-negligible contributions to the magnetizability tensor, which are sensitive to the gauge origin and basis set chosen [C. van Wu?llen, J. Chem. Phys. 136, 114110 (2012)]. These terms were neglected in previous calculations as they were assumed to be small. In this paper we analyze the importance of the gauge-dependent semi-local pseudopotential correction term in detail for AuF and clusters of Sn showing that it leads indeed to very large corrections to the paramagnetic term for large-core pseudopotentials. Without this correction the results become very sensitive to the basis set applied. This now resolves some of the unusual large paramagnetic contributions reported before for both AuF and Sn(2).     

Renner-Teller vibronic analysis for a tetra-atomic molecule. I. The effective Hamiltonian and matrix elements

The effective vibronic Hamiltonian for a linear tetra-atomic molecule in a Pi state has been investigated. In addition to the usual vibrational and Renner-Teller coupling terms, the bending mode anharmonicity, spin-orbit coupling, and Fermi resonance interactions have been added to the model. Terms in the Hamiltonian up to the fourth order are given explicitly for molecules of C(infinityupsilon) symmetry and simplifications for symmetric D(infinityh) molecules are discussed. The matrix elements for the HCCS free radical have been obtained and are used to analyze the observed ground-state levels of HCCS and DCCS in a companion paper. The Sears resonance vibronic interaction that couples levels with the selection rules DeltaK=+/-1, DeltaSigma=-/+1, and DeltaP=0 has also been studied and the matrix elements derived. The determinable combinations of signs for the major parameters in the model are discussed.