Ruling out harmonic couplings as a possible origin of an anomalous isotope effect on the ν5modes in H bonds

Measurements of the transition probabilities of all the IR bands of adipic acid crystals, polarized in the a, c plane and having frequencies in the range 1000–4000 cm^?1show that the anomalous value P_H/P_D= 2 found for the ratio of the transition probabilities of ν_s bands

and

cannot be due to a harmonic coupling of ν_s vibrations with other vibrations.     

On the Pauling electronegativity scales—I

It is shown that the Pauling electronegativity scale χ is closely related to the electrostatic potential near the physical meaningful boundary between the core and valence regions in an atom, and is well reproduced by the relationship:

where N_ν is the valence electron number and the factor f(n) is empirically given by

n being the periodic number.     

Zur komplexchemie von 4-zentren-π-systemen : XII. Glyoxaldiiminkomplexe: 1H-nmr-spektren und long range-kopplungen

Glyoxaldiimines (I) RN=CHCH=NR show in the NMR a downfield shift of glyoxalic protons (H_gly) when complexed to

(II: M = Mo, W), but increasing high field shifts when going to

(III) and

complexes (IV). In the tungsten complexes II H_glyW coupling satellites are resolved (J(WH) ≈4–6 Hz); in the phosphine compounds III, IV long range PH_gly coupling is clearly visible. Mechanisms of spinspin interaction are briefly discussed in connection with the EPR results on monoanionic radicals of II–IV.     

Sensitized photochemical reactions of some silyl-1,3-butadienes: Synthesis of 2,2,4-trimethyl-3-methylene-2-silabicyclo [2.1.1]Hexane

The photolysis of 2,4,4-trimethyl-4-sila-3-methylene-l,5-hexadiene

yielded 2,2,4-trimethyl-3-methylene-2-silabicyclo[2.1.1]hexane as the only volatile photoproduct in high yield. However, 2,4,4-trimethyl-4-sila-3-methylene-1,6-heptadiene

was found to be photochemically non-reactive under identical reaction conditions, and the 1-substituted butadienes (VI) and (VIII)

underwent cis-trans isomerism on photolysis.     

Investigation of the 2B2 state of H2O+ using valence-bond techniques

Ab initio valence-bond calculations have been performed on the low-lying states of H₂O⁺, with special attention being focused on the

²B₂ state of the ion. The calculated potential energy surface for the

²B₂ state is in qualitative agreement with several previously published molecular orbital calculations in predicting an equilibrium angle of about 60°. This prediction is, however, inconsistent with the most recent interpretation of the high-resolution photoelectron spectrum of H₂O. Examination of the potential energy surfaces for geometries which have been distorted from C_2v symmetry indicates that the

²B₂ and òA₁ states are strongly coupled by the asymmetric stretching motion of the molecular ion. The presence of such a coupling supports the interpretation of the H₂O photoelectron spectrum which invokes excitation of the asymmetric stretching vibration of the ion.     

Further evidence for the intramolecular charge-transfer interaction between tropylium ion and remote benzene rings in 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborate and its methyl derivatives

A series of 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborates

has been prepared. The intramolecular charge-transfer interactions in

were confirmed by their UV spectra and pK_R+ values. As a model compound 1,2,3,4-tetrahydro-1,4-(1,2-tropylio)naphthalene tetrafluoroborate ($\text{5}$)_was also examined.     

Reply to comment by J.T. Wang and F. Williams on the stability of alkyl halide and related σ* anions

Conditions under which σ^* anions (R^.-hal)^? are likely to be stable with respect to dissociation into R^. + hal^? are discussed. It is pointed out that if dissociation leads to

+ hal^., then an important factor is the shape of

rather than that of R^..     

Laser flash photolysis of iodine-iodide mixture in hydroxylic solvent. Evidence for the existence of the radical anion I

The laser flash photolysis of iodine-iodide mixtures in alcoholic solvents produces transient species absorbing in the red and near infrared region with maxima at 740 and 590 nm. The 740 nm absorption band has already been attributed to the well known I

ion. In this work the 590 nm absorption band is assigned to the I

radical anion which presumably could be formed by the equilibrium reaction: I

+ I₃^- ? I

. The variations of the intensities of the 590 and 740 nm transient absorption bands as a function of I₃^? concentration, temperature and solvent, support this assignment. The kinetics of formation of I

and I

has been studied in solutions of tertiary butanol. An analysis of the experimental results shows that the I

ion could be formed via a mechanism involving an I

intermediate.     

The effect of the simultaneous variation of sample mass and heating rate in DTA and DSC

Quantitative correlations between kinetic parameters (energy of activation, E), procedural factors (sample mass, m, and heating rate, φ) and the dependent variables (the temperature of inception of reaction, T_i, and temperature T_α at which a constant fraction α has decomposed) have been derived for differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The relations have the same form as those derived from earlier TG studies. The dependent variables T_i and T_α are related to m, φ and E by the equations

where C₃ and C₂ are constants, and

where C₄ and C₅ are constants for a given α. The variation of C₅ with α is given by C₅ = a + b α where a and b are constants. The equations are applicable to TG, DTA and DSC.     

Electrogeneration of triplet states of intramolecular anthracene-amine systems

In the electron transfer between the cation radicals

of the amine moiety of four intramolecular anthra cene-amine systems and the anion radicals B^XXX of some heterocyclic and carbonyl compounds in acetonitrile/toluene, the triplet state of the anthracene moiety

is formed. As intermediates in this process, intramolecular and intermolecular triplet exciplexcs

or

and

or

are discussed.     

The electroreduction of 2- and 3-cyanopyridinium ions

The reduction mechanism of 1-alkyl-2-cyanopyridinium (2(CN)⁺) and 1-alkyl-3-cyanopyridinium (3(CN)⁺) has been investigated in acetonitrile using dc, normal pulse (NP) and reverse pulse polarography (RP).The reduction of 2(CN)⁺ at low concentraions (< 4 × 10⁻⁵M) and short pulse widths (t_p < 2 ms) leads to the formation of the radical 2(CN) in a reversible process with E°′ = −1028±2 mV.

At longer times, dimerization of the radicals occurs at the 2-, 4- and 6-positions, leading predominantly to 4,4′- and 4,2′-dimers (all dimers denoted by D(CN)₂).

Fast interconversion of linking positions takes place. 4,4′-Dimers are the predominant species. 2,4′-Dimers, although minor species, enable a path for one cyano group to be lost in a homogeneous reaction, resulting in a new pyridinium ion, D(CN)⁺. This pyridinium ions is reduced further at potentials more negative than 2(CN)⁺.

Cyanide ions react with 2(CN)⁺ to form 2,4-dicyano-1-methyl-1,4-dihydropyridine.

The rate of this reaction is relatively slow in the presence of LiClO₄ (k_f = (8±0.5) s⁻¹M⁻¹, k_b = (2.3±0.2)×10⁻³ s⁻¹, log (K/M⁻¹)=(3.5+0.1)) and is much faster in TBAP. During the electrochemical reduction of 2(CN)⁺, during which cyanide ions are released, reaction (5) takes place, causing a decrease in the polarographic limiting current in TBAP, but not in LiClO₄.The reduction of 3(CN)⁺ consists of a single charge transfer followed by irreversible dimerization.

     

Dynamical LEED study of C2H2 and C2H4 chemisorption on Pt(111): evidence for the ethylidyne group

We propose ethylidyne

as the stable formed from C₂H₂ and C₂H₄ chemisorption on the Pt(111) surface (T ≈ 300–350 K). Consistent evidence to support this proposal is given by LEED intensity analysis and high resolution ELS studies of this species.     

Formation of methylpropargyl radicals from tetramethylcyclobutadiene radical cations: an esr study

Exposure of dilute solutions of CH₃CCCH₃ in CC1₂FCC1F₂ and related solvents to ionizing radiation at 77 K produced the radical cation (CH₃CCCH₃)⁺. On annealing, these were initiallycpnverted into the corresponding dimer cation, c-C₄(CH₃)₄⁺, which subsequently decomposed to give the propargyl radical

. This novel result is supported by studies using CH₃CCCD₃ which gave, finally, the radicals

and

in a ratio of approximately 9:1. The absence of the radicals

and

indicates that the cyclobutadiene ring is strongly distorted (D_2h) and that the initial dimers do not undergo equilibration via symmetrical dimers under our experimental conditions. These results are compared to liquid-phase data for c-C₄(CH₃)₄⁺ radicals and explanations for the differences in behaviour are proposed.     

The triplet state decay (T1(nπ*) → S0) of benzaldehydes in the dilute gas phase

The triplet T₁(nπ^*) decay of benzaldehyde (B) and its isotopomers

and

were investigated in the dilute vapour phase (≤0.5 Torr) at room temperature. Following

excitation the quantum yields of the phosphorescence and photodecomposition, and the rate constants of the phosphorescence and the radiationless T₁ → S_o process were determined. Based on these results and in conjunction with theoretical calculations of T₁ → S_o rates and previous data obtained on propynal, the decay mechanism of benzaldehyde was analyzed. It is shown that the important accepting modes of the non-radiative T₁ → S_a decay are the

wagging and the CO stretching modes. In spite of the close vicinity of the T₂(ππ^*) and the T₁(nπ^*) states, the non-adiabatic coupling (communication between ring and carbonyl vibrations is not sufficient to influence the relaxed T₁(nπ^*) decay significantly.     

Étude de la conformation des tripeptides en solution dans l'eau lourde par spectrométrie infrarouge

An IR spectroscopic study of dipeptides

and tripeptides

(where R₁ R₂ R₃ can be H or CH₃) in their zwitterion, chlorohydrate or alkaline forms in heavy-water solution, has shown that the first two forms of the tripeptides exist in the C⁵ conformation; in alkaline solution the hydrogen bond responsible for this conformation is broken. It is shown that the end groups, CO₂^? or CO₂D, possess stretching vibration frequencies which characterize the terminal ammo-acid. Similarly, bending vibration frequencies of CH₂ or CH₃ groups depend on the CH₂ or CH₃ position in the peptide chain.     

Complex hydrogen bonded cations: I. The pyridinium-pyridine ion

The occurrence of the (py₂H)⁺ ion in solutions containing pyridinium ion and pyridine has been established spectroscopically.The infrared and Raman spectra of the four species

,

,

, and

have been examined in the range 80–6000 cm^?1. The spectra are independent of concentration, solvent, or counterion if this is inert. The NH stretching band is a strong, broad doublet with maxima at 2080 and 2530 cm^?1. In the bridge deuterated species there is a single strong, broad, ND stretching band, maximum at 1920 cm^?1. The N-N stretching is infrared active, at ~138 cm^?1. The internal modes of the base are all singlets in both the infrared and Raman spectra. The proton bridge is between the σ orbitais on the N atoms.     

Electrokinetic phenomena in porous membranes: Determination of phenomenological coefficients and transport numbers

Electrokinetic phenomena in porous membranes were studied in the framework of the linear thermodynamics of irreversible processes. Phenomenological coefficients of two commercial porous membranes were determined. The variation of these coefficients with the different concentrations of NaCl used was also studied. Onsager's reciprocal relationship between cross-coefficients holds within the limits of experimental error.Membrane potentials were measured at concentrations ranging from 10^?3M to 75 X 10^?3M. The apparent transport number of the cation,

, was calculated from the diffusion potential expression. An electrometric method was used to obtain the true cation transport number,

, and the water transport number,

, for different solution concentrations, ranging from 15 x 10^?3M to 75 x 10^?3M. The true transport number of the cation,

, was also determined, taking into account water transport across the membrane. A good agreement was found between

and

values.     

A direct synthesis of 1,3-bis(bromomagnesio)propane

Careful addition of 1,3-dibromopropane

to magnesium in Et₂O yields 1,3-bis(bromomagnesio)propane

which is purified via “magnesacyclobutane”

. Reactions of

with H₂O, CO₂, HgBr₂ and Me₃SnCl are reported. MgBr₂ catalyses the decomposition of

to allylmagnesium bromide

.     

Doping-addition of arylsulfenyl chlorides to the tricyclo[4,2,2,02,5]deca-3,7,9-triene system: skeletal rearrangements and serendipitious products

“doping-addition” of 2-NO₂C₆H₄SCl to the tricyclo[4,2,2,0^2,5]deca-3,7,9-triene system

occurs to give unusual products: (i) rearranged caged cyclopropane

and (ii) the stable cross-perchlorate

.