THE EFFECT OF ACIDS ON THE INFRARED SPECTRA OF SCHIFF BASES—II. IMINES CONTAINING THE C=C-C=N AND C=C-C=C-C=N UNITS

Abstract— The Fourier-transform infrared spectra of chloroform-d solutions of conjugated imines CH₃CH=CHCH=NCH(CH₃)₂ and CH₃CH₂CH=CHCH=CHCH=NCH(CH₃)₂ and the related protonated species with HCl, HBr, HI, trichloro, dichloro, monobromo and monochloroacetic acids or propionic acid are presented. The effects of conjugation and protonation are examined. The results show that conjugation slightly increases the basicity of the Schiff bases. HCl, HBr and HI protonate the Schiff bases completely. The carboxylic acids protonate partially depending on their p K _a, values. When the Schiff base contains two (or more) C=C bonds conjugated with C=N, the main C=C stretching band undergoes a strong intensification showing that sizeable dipole moment variations occur along the conjugated chain.     

An improved boundary element method for the charge density of a thin electrified plate in ℝ3

A weakly singular integral equation of the first kind on a plane surface piece Γ is solved approximately via the Galerkin method. The determination of the solution of this integral equation (with the single-layer potential) is a classical problem in physics, since its solution represents the charge density of a thin, electrified plate Γ loaded with some given potential. Using piecewise constant or piecewise bilinear boundary elements we derive asymptotic estimates for the Galerkin error in the energy norm and analyse the effect of graded meshes. Estimates in lower order Sobolev norms are obtained via the Aubin–Nitsche trick. We describe in detail the numerical implementation of the Galerkin method with both piecewise-constant and piecewise-linear boundary elements. Numerical experiments show experimental rates of convergence that confirm our theoretical, asymptotic results.     

Surfactants with an amide group "spacer": Synthesis of 3-(acylaminopropyl)trimethylammonium chlorides and their aggregation in aqueous solutions

The cationic surfactants RCONH(CH2)3N+(CH3)3Cl-, where RCO = C10, C12, C14, and C16, respectively, have been synthesized by reacting the appropriate carboxylic acids with 3-N,N-dimethylamino-1-propylamine, followed by dehydration of the ammonium salt produced. Reaction of the intermediates obtained (RCONH(CH2)3N(CH3)2) with methyl iodide, followed by chloride/iodide ion-exchange furnished the surfactants. Their adsorption and aggregation in aqueous solutions have been studied by surface tension, conductivity, EMF, static light scattering and FTIR. Additional information on the micellar structure was secured from effects of the medium on the 1H NMR chemical shifts and 2D ROESY spectra. Increasing the length of the acyl moiety increased the micelle aggregation number, and decreased the minimum area/surfactant molecule at the solution/air interface, the critical micelle concentration, and the degree of dissociation of the counter-ion. Gibbs free energies of adsorption at the solution/air interface and of micelle formation were calculated, and compared to those of 2-(acylaminoethyl)trimethylammonium chloride; alkyl trimethylammonium chloride; and benzyl(3-acylaminopropyl)dimethylammonium chloride surfactants. For both processes (adsorption and micellization), contributions of the CH2 groups in the hydrophobic tail and of the head-group to DeltaG0 were calculated. The former contribution was found to be similar to those of other cationic surfactants, whereas the latter one is more negative than those of 2-(acylaminoethyl)trimethylammonium chlorides and trimethylammonium chlorides. This is attributed to a combination of increased hydrophobicity of the head-group, and (direct- or water-mediated) intermolecular hydrogen-bonding of aggregated monomers, via the amide group. FTIR and NMR results indicated that the amide group lies at the micellar interface.     

An implicit finite-difference algorithm for the numerical simulation of supersonic flow over blunted bodies

In order to compute axisymmetric laminar supersonic flow we use an unsteady implicit finite-difference scheme. This scheme solves numerically either the inviscid Euler equations or the ‘thin-layer’ Navier-Stokes equations. In both cases the scheme leads to large sparse non-linear systems, which can be solved by a genuine iteration process. The convergence of this process is shown and numerical results are given.