Computationally‐Assisted Approach to the Vibrational Spectra of Molecular Crystals: Study of Hydrogen‐Bonding and Pseudo‐Polymorphism

Abstract

Zwei Stufen, ein Katalysator: Ein Vanadium(V)‐Oxo‐Komplex mit einer dreizähnigen Schiff‐Base als weiterem Ligand katalysiert die Titelreaktion, die racemische (Bis)homoallyl‐α‐hydroxyester in trans‐Tetrahydropyrane (THPs) oder cis‐Tetrahydrofurane (THFs) überführt. Auf diese Art lassen sich cyclische Ether effizient asymmetrisch synthetisieren, wie mit der ersten enantioselektiven Synthese von (−)‐Pantofuranoid E belegt wird.

Hydrated Solid Forms of Theophylline and Caffeine Obtained by Mechanochemistry

“…The O-H stretching frequency of water was observed at 3360 cm -1 for the theophylline hydrate and at 3357 cm -1 for the caffeine hydrate. The IR spectra of theophylline and caffeine hydrates were similar to the reported previously [12]. …”

Probing Pseudopolymorphic Transitions in Pharmaceutical Solids using Raman Spectroscopy: Hydration and Dehydration of Theophylline

“…Based on this information, the band was assigned to the metastable form TPm. 65 On the whole, the two experiments (weighting and FT-Raman measurements) are consistent with a two-step mechanism for the pseudomorphic TPh ! TPa transformation…”

“…As can be seen, the spectral differences between the TPa and TPh forms spread out through almost the entire spectral range. According to a previous study, 65 these are related to the stretching modes of the oscillators C (8) All these spectral regions were evaluated for their suitability to be used in the relative quantification of the two forms, TPa and TPh, using physical mixtures of known TPa/TPh ratio. Two main criteria were considered.…”

“…The remaining spectral regions marked in Figure 3 either do not present a single isosbestic point or include Raman bands ascribed to Fermi resonance modes, 65 and thus preclude a kinetic analysis.…”

Pseudopolymorphic transitions of niclosamide monitored by Raman spectroscopy

“…Ab initio calculations using a molecular pair approach 22 can be used to predict the shifts associated with pairwise intermolecular contacts, and assist a full vibrational assignment of different crystal forms. Although such assignment is out of the scope of the present work, calculations with a few pairs suggest that the observed shifts may result from the increase of hydrogen bond contacts of the OH group (for instance, due to niclosamide Ð Ð ÐH 2 O association) and the decrease of hydrogen bond contacts of the C O group.…”