Detailed Assignment of the CH Chromophores in Methyl Mandelate and Mandelic Acid: A Multi-Experimental Approach Using Polarized FTIR Microspectroscopy of Sublimated Crystals

Abstract

A sublimation cell for the characterization of microcrystals using Fourier transform infrared (FTIR) microspectroscopy was constructed and applied to methyl mandelate and mandelic acid. It was possible to assign different CH chromophores in the FTIR spectra. Comparison to quantum chemical calculations, attenuated total reflectance infrared (ATR-IR) spectra of related compounds, and isotope labeling was used to support the assignments. Vibrational transition dipole vectors were deduced from crystal rotation and polarization experiments. The direction of these vectors can be used to constrain the absolute orientation of the molecules in the crystal as well as for the assignment of further vibrational bands.

Femtisecond single-mole infrared spectroscopy of molecular clusters

“…Important challenges for future jet-FTIR studies include the extension into the very far infrared range, 139 where weak translational bands meet low photon levels, and into the near infrared, 117 where the band strengths are extremely small. Using focal plane array detectors, 221 it will become possible to directly image a supersonic jet expansion in terms of spatial cluster distribution or shock waves. Presently, this is restricted to a pointwise scanning mode.…”

Rotational spectroscopy of methyl benzoylformate and methyl mandelate: structure and internal dynamics of a model reactant and product of enantioselective reduction

“…16 More recently, based on resolved OH stretching vibrational bands of MM in n-hexane, Tsui et al distinguished two intramolecular hydrogen bonding scenarios: OH hydrogen-bonded to the sp 3 -hybridized oxygen atom of the ester group (OHÁ Á ÁO-C); and OH hydrogen-bonded to the sp 2 -hybridized oxygen atom of the carbonyl group (OHÁ Á ÁOQC). 19 Furthermore, Nedić and Suhm characterized crystalline MM using Fourier-transform infrared microspectroscopy, 20 and Poopari et al characterized solvated MM using vibrational circular dichroism. 18 Albrecht et al followed up on this study by investigating self-aggregation of MM, using a wide variety of spectroscopic methods.…”

Adaptive Aggregation and Chirality Recognition of Neuroactive Substances and their Building Blocks: A Vibrational Spectroscopic and Microscopic Study

“…The synthesis of mandelates according to Refs. [57,58] was modified to obtain methyl-d 3 mandelate [37]. 0.458 g R-mandelic acid (0.0030 mol) was dissolved in 3 mL methanol-d 3 (0.0742 mol, 25-fold molar excess).…”

“…Methyl mandelate was chosen as the test substance for the polarized transmission FTIR microspectroscopic studies on sublimated crystals because of its structural similarity to some neurotransmitters [37]. Results including the change of conformation and chirality recognition of a 1:1 and a 3:1 racemic crystal [38] are presented in Chapter 5.…”

“…The polarized transmission FTIR microspectroscopic method is applied to mandelic acid [37] in Chapter 6 and to the neuroactive phenylpropanolamines norephedrine, pseudonorephedrine, ephedrine, and pseudoephedrine in Chapter 7. Chirality recognition effects are presented for norephedrine and pseudoephedrine.…”