Chirality‐Induced Switch in Hydrogen‐Bond Topology: Tetrameric Methyl Lactate Clusters in the Gas Phase

Abstract

Supersonic jet expansions of racemic methyl lactate show a prominent OH‐stretching infrared absorption at 3401 cm−1 which is not present in the enantiopure compound. Experimental results and quantum chemical calculations show that the underlying tetrameric cluster has 2:2 stoichiometry of the R and S isomers and S4 symmetry (see picture; C orange, O red, H gray).

Chirality Recognition between Neutral Molecules in the Gas Phase

“…Usually, cooperativity wins for larger clusters, but there are stereoselective exceptions which offer stabilizing secondary interactions. [139] …”

“…[141] However, the effect is very pronounced at the MP2 level. [139] The structure loses its competitiveness by replacing the C a ÀH atom with a methyl group, whereas it can also be realized in MGly tetramer. [93] Interestingly, the crystal structures of enantiopure and racemic serine also differ in the type of hydrogen bonding, O À H···O À H versus O À H···O = C. Like racemic lactate tetramers, racemic serine can form OÀ H···O=C links.…”

“…There is one exception: The tetramer built from two R and two S units in an alternating RSRS sequence, switches back to the OÀH···O=C connectivity, giving rise to a characteristic IR band. [139] This change is due to a particularly compact S 4 -symmetric structure (Figure 9), which offers a maximum of attractive secondary interactions. To build the structure, the internally hydrogen-bonded OH group in neighboring syn lactate units has to be distorted in alternating directions (r/s) and this alternation has to match the alternation of the lactate configuration (R/S).…”

Confinement of chiral molecules in reverse micelles: FT-IR, polarimetric and VCD investigation on the state of dimethyl tartrate in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles dispersed in carbon tetrachloride

“…On the other hand, when dimethyl-d-tartrate is solubilized in 0.158 M AOT/CCl 4 solutions, the OH band appears broadened and red-shifted suggesting extensive intermolecular H-bonding which, being unconstrained by intramolecular tensions and enhanced by cooperative effects, allows to establish stronger H-bonds as well as to widen the spectrum of differently hydrogen bonded DDT populations [14]. This finding can be taken as a clear indication that DDT is entrapped in the polar domain of the AOT reverse micelles leading to strong DDT/DDT and DDT/AOT interactions.…”

MOVIPAC: Vibrational spectroscopy with a robust meta‐program for massively parallel standard and inverse calculations

“…[29,33,52] Subspace iteration methods for vibrational problems have been used before in the context of molecular mechanics applications, [53][54][55][56] where huge Hessians must be diagonalized and where subspace iteration techniques are a natural means to solve the diagonalization problem. In quantum chemistry, however, the Mode-Tracking idea established new principles [28,[57][58][59][60][61][62][63] : (1) isolated, structure-characteristic vibrations can be directly targeted, (2) vibrations that involve only a subset of atoms (e.g., in the case of adsorbates on surfaces [64] or in quantum mechanics (QM)/molecular mechanics (MM) partitionings [65] ) can be directly optimized, (3) low-dimensional Hessians also benefit if their entries are time-consuming to calculate. In our former work, [51] it was shown that the proper construction of a guess vector has an important influence on the convergence characteristics of the algorithm.…”