Optically active amines. XVI. Exciton chirality method applied to the salicylidenimino chromophore. Salicylidenimino chirality rule

Abstract

The Cotton effects of A-salicylidene derivatives of chiral a-and /3-arylalkylamines are interpreted in terms of a coupled oscillator mechanism. The exciton splittings in the circular dichroism (CD) spectra of the Ar,Ar'-di(5-bromosalicylidene) derivative of (R)-(-)-imns-l ,2-cyclohexanediamine and the N,N'-di(5-bromosalicylidene) and A^A'-disalicylidene derivatives of (R)-(-)-l ,2-propanediamine are utilized to determine the transition moment directions for the salicylidenimino chromophore. A simple chirality rule is then devised for A-salicylidene-/3-arylalkylamines, stating that the sign of the Cotton effects near 255 and 315 nm (or the long wavelength band in the case of exciton splitting) is the same as the sign of the chirality (right-handed screw for positive chirality) of the attachment bonds to the aryl and salicylidenimino groups. Agreement is shown with the CD data for ßarylalkylamine derivatives for which the aryl substituent is a phenyl, p-nitrophenyl, p-hydroxyphenyl, or p-chlorophenyl group. For the A-salicylidene derivatives of a-arylalkylamines, the sign of chirality is determined by placing the transition moments at the center of the aryl group and of the phenyl ring of the salicylidenimino chromophore. Again positive chirality gives positive Cotton effects near 255 and 315 nm if the interaction energy is positive. Agreement is shown with the CD data for chiral -arylalkylamine derivatives for which the aryl substituent is a 1-naphthyl, phenyl, 2-pyridyl, or 4-pyridyl group. For the A-salicylidene derivatives of chiral alkylamines, the one-electron mechanism accounts for the observed Cotton effects. Consequently, the C, symmetry of the salicylidenimino chromophore suggests the application of a planar sector rule.

Copper(II) Schiff base complexes and their mixed thin layers with ZnO nanoparticles

“…Powder X-ray diffraction (PXD) analysis was performed using a Philips (Almelo, The Netherlands) XPERT θ-2θ diffractometer with CuKα radiation. The indentation properties of the layers were made on NHT2 microindentation tester (TTX-NHT) from Anton Paar TriTec SA with a Berkovich indenter using loads 20 and 100 mN and holding time of 5 s. The system hardness and elastic modulus were determined from the indentation curves by the standard Oliver [35][36][37][38][39][40] (vs, very strong; s, strong; m, medium; w, weak, vw ver weak) (figure 1).…”

Probing the mechanism and dynamic reversibility of trianglimine formation using real‐time electrospray ionization time‐of‐flight mass spectrometry

“…Compounds 1 , 4 , 5 , 19 and 31–33 (Figs. and , and Scheme ) were synthesized according to standard published procedures . Positive ion mode mass spectra of the samples dissolved either in MeOH (methanol) or in DCM (dichloromethane) were recorded on a ESI‐TOF mass spectrometer (Bruker Daltonics, Bremen, Germany).…”

“…1 and 6, and Scheme 4) were synthesized according to standard published procedures. [9,18,28] Positive ion mode mass spectra of the samples dissolved either in MeOH (methanol) or in DCM (dichloromethane) were recorded on a ESI-TOF mass spectrometer (Bruker Daltonics, Bremen, Germany). Calibration was carried out using a 0.1 M solution of sodium formate in the enhanced quadratic mode prior to each experimental run.…”

Optically pure trans-1-benzyl-4-aminopiperidin-3-ols. Synthesis and absolute configuration

“…As it is shown in Figure 3, three Cotton effects in the CD curve of derivative 9a -negative at 322 and 250 nm and positive at 276 nm -are attributed to transitions of the salicylidenimino chromophore with an intramolecular hydrogen bond. 16 For the Nsalicylidenimino derivative 9a, the observable negative Cotton effects at 322 and 250 nm correspond to the negative sign of chirality; thus, derivative 9a has the (3R,4R) configuration. The CD spectrum 9b in CDCl 3 exhibits an almost mirror image of the 9a spectrum: there are less intense positive Cotton effects at 322 and 250 nm (room temperature), which correspond to positive chirality (Fig.…”