Chiral Discrimination by Vibrational Spectroscopy Utilizing Local Modes

Abstract

Chiral discrimination of homochiral and heterochiral H-bonded complexes is a challenge for both experimentalists and computational chemists. It is demonstrated that a two-pronged approach based on far-infrared vibrational spectroscopy and the calculation of local mode frequencies facilitates the chiral discrimination of H-bonded dimers. The local H-bond stretching frequencies identify the strongest H-bonds and by this the dominating chiral diastereomer. This is shown in the case of peroxide, trioxide, hydrazine, glycidol, and butan-2-ol dimers as well as propylene oxide···glycidol complexes investigated with the help of second-order Møller-Plesset perturbation, coupled cluster, and density functional theory calculations where, in the latter case, the ωB97X-D functional was used for an improved description of H-bonding. In some cases, additional intermolecular interactions overrule the important role of H-bonding, which is found by calculating chirodiastaltic energies.

Quantitative Assessment of B−B−B, B−Hb−B, and B−Ht Bonds: From BH3 to B12H122−

“…It has been shown that the local stretching force constant k a is a superior bond strength measure compared to the often used bond dissociation energies (BDE) and bond dissociation enthalpies (BDH) as they contain cumulative effects of geometry relaxation, multiple bonding interactions, and also electronic density reorganizations of the dissociated fragments . Local stretching force constants k a have been successfully used to determine the intrinsic bond strength of covalent bonds such as: CC bonds, NN bonds, NF bonds, CO bonds, and CX (X=F, Cl, Br, I) bonds, and weak chemical interactions such as: hydrogen bonding, halogen bonding, pnicogen bonding, chalcogen bonding, tetrel bonding, and recently interactions …”

“…[25,[73][74][75] It has been shown that the local stretching force constant k a is a superior bond strength measure compared to the often used bond dissociation energies (BDE) and bond dissociation enthalpies (BDH) as they contain cumulative effects of geometry relaxation, multiple bonding interactions, and also electronic density reorganizations of the dissociated fragments. [73,76,77] Local stretching force constants k a have been successfully used to determine the intrinsic bond strength of covalent bonds such as: CC bonds, [74,75,78,79] NN bonds, [80] NF bonds, [81] CO bonds, [82] and CX (X = F, Cl, Br, I) bonds, [83][84][85][86] and weak chemical interactions such as: hydrogen bonding, [87][88][89][90] halogen bonding, [91][92][93] pnicogen bonding, [94][95][96] chalcogen bonding, [73,77] tetrel bonding, [97] and recently BH � � � p interactions. [16,17] The main objectives of this paper are: (i) to evaluate the nature of the BÀ B, BÀ H b , and BÀ H t bonds; (ii) to evaluate why intermediate species may or may not facilitate the reversibility reactions in the perspective of thermodynamics and intrinsic bond strength; (iii) to provide a new tool to characterize new (potential) intermediates and their role for the reversibility of the hydrogenation/dehydrogenation reactions; and (iv) to give guidelines whether intermediates may be stable enough to be isolated.…”

Vibrational Properties of the Isotopomers of the Water Dimer Derived from Experiment and Computations

“…[19][20][21][22][23] This approach is especially attractive when applied to H-bonded complexes [24] and when measured vibrational frequencies, rather than calculated vibrational frequencies, are available. [25,26] In this work, we will extend the description of molecular properties based on measured vibrational frequencies to determine the vibrational properties of isotopomers of a given target molecule.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…One has however to keep in mind that systems deprived of very floppy or anharmonic motions, like those made of rigid subunits or involving a dominant electrostatic interaction, are very satisfactorily described in terms of harmonic frequencies of the most stable isomers [184]. Last, attempts at assessing the chiral discrimination effects in terms of local mode description have been proposed but not applied to experimentally studied systems yet [185].…”