Synthesis, spatial and electronic structure of 1-(+)-neomenthyl-1,2-diphosphole and 1-(+)-neomenthyl-1,2,4-triphosphole tungstenpentacarbonyl complexes

Characterization of Conjugation Effects in the Series of Quinoxaline-2-ones by Means of Vibrational Raman Spectroscopy

“…However, it is worth mentioning that the accurate experimental measurement of Raman intensity is a challenging task, which can be influenced by the scattering conditions, the inhomogeneity of the sample, the proximity of the wavelength of the excitation line to the absorption bands of the chromophores, their colors, etc. Conversely, quantum chemically calculated Raman intensities are not affected by these factors and can be used instead of their experimental counterparts as shown previously. − ,− ,, The good agreement of the calculated relative Raman intensities with the corresponding experimental ones also reinforces the confidence in the reliability of the approach used. Herein we employ this protocol to our Q species, in particular focusing to rather characteristic and conserved vibrations such as the “νC N ”, whose normal mode vector representation is given in the Supporting Information.…”

“…Conversely, quantum chemically calculated Raman intensities are not affected by these factors and can be used instead of their experimental counterparts as shown previously. [48][49][50][51][52][54][55][56][57][58]74,81 The good agreement of the calculated relative Raman intensities with the corresponding experimental ones also reinforces the confidence in the reliability of the approach used. Herein we employ this protocol to our Q species, in particular focusing to rather characteristic and conserved vibrations such as the "νCN", whose normal mode vector representation is given in the Supporting Information.…”

“…The harmonic vibrational frequencies and Raman activities, for simulations of the Raman spectra, were calculated using the popular Becke’s three-parameter exchange functional in combination with the Lee–Yang–Parr’s correlation functional (B3LYP). As demonstrated elsewhere ,,− ,,,, B3LYP offers the most cost-effective choice for the calculation of Raman spectra of organic molecules. In particular, the relative Raman activities for the bands in the frequency range ν ≤ 2300 cm –1 are better predicted by this hybrid functional than by ab initio second order Möller-Plesset perturbation theory (MP2) .…”

“…The spectral-structural relationship and in particular the coupling with the extent of the π-conjugation effects, both in solutions and solid state, are provided and analyzed, also thanks to the analysis of the experimental spectra performed by DFT calculations to unravel the nature of the electronic density reorganization and its role on the conjugation pattern. Such an approach based on the combinations of experimental and theoretical protocols, allows both a reliable assignment of the observed Raman bands and, more importantly, a semiquantitative evaluation of the conjugation strength within the molecular backbone. ,,− Indeed, the intensity of Raman bands is closely connected with the extent of the conjugation within a given molecule, and, as it will be briefly recalled in the following section, conjugated systems show a many-fold increase in the intensity of the polarized bands corresponding to the symmetric stretching vibrations of the bonds participating in the conjugation. Thus, the intensities of these enhanced Raman bands can be considered as observables providing an estimation of the strength and of the length of conjugation. ,− Moreover Raman spectroscopy provides an efficient tool tightly interconnecting conjugation effects with the inherent characteristics of the different excited electronic states, since the intensity of a selected Raman band formally depends on the properties, and especially the transition dipole moments, of all the electronic excited states. ,− Hence, in this work through the analysis and the identification of the most conjugation-sensitive Raman scattering bands in a series of novel Q-derivatives we provide a practical way to achieve a semiquantitative characterization of the conjugation length of these compounds, while identifying the effect of conjugation on the optical properties of the Q-derivatives.…”

Review on asymmetric cycloaddition reactions at phosphorus (III) atom

“…11 At the same time, asymmetric Diels-Alder reactions of 1-(+)-neomenthyl-3,4,5triaryl-1,2-diphosphole (1b) with maleic acid derivatives proceeded with higher diastereoselectivity (up to 91% de) and results in the corresponding enantiopure 1,7-diphosphanorbornenes 3 after recrystallization. [12][13][14] An analysis of the structure of 1-(+)-neomenthyl-3,4,5-triphenyl-1,2-diphosphacyclopenta-2,4-diene (1b) indicated that steric shielding of one side by the bulky isopropyl group causes a preferential approach of the dienophile from the opposite side resulting in one attractive and one repulsive pathway of the [4+2] cycloaddition reaction. This study approves that getting closer of the chiral inductor with the dienic system of 1,2-diphospholes leads to an increase of stereochemical outcome (de) of hetero-Diels-Alder reaction.…”