Structural Elucidation of Trace Amounts of Volatile Compounds Using the Crystalline Sponge Method

Abstract

Volatile organic compounds are widely present as scents and odors in our daily lives and are readily found in a variety of natural extracts. Because these compounds are highly volatile and usually available only in minute quantities, little attention has been paid to X-ray diffraction as a technique for their structure determination. Here, we show that the structures of volatile organic compounds are easily elucidated using minute quantities of the compounds and the crystalline sponge method. The compound vapors can be directly absorbed into the sponge crystals, or alternatively, preparative gas chromatography can be used to separate the desired compound from a natural mixture.

Racemic and Enantiopure Camphene and Pinene Studied by the Crystalline Sponge Method

“…Only unidentifiable small fragments of unordered solvent and/or (+)-α-pinene molecules were found inside the channels. This result is in agreement with the observation of the group of Fujita 22 for α-pinene. The absence of the original chloroform solvent molecules in the structure indicated, however, that guest exchange had occurred.…”

“…Others observed that enantiopure compounds can be ordered inside the host channels and give rise to loss of inversion symmetry, possibly aided by solvents. 2 , 22 , 25 − 27 This is indeed the case for β-pinene but we did not observe this for camphene and α-pinene. It is not clear if ordering of enantiopure compounds or of enantiomeric pairs is most common.…”

Structure determination of terpenes by the crystalline sponge method

“…These interactions include π-π, CH-π, and charge-transfer interactions. The technique was first introduced by Fujita et al [1] in 2013 and since then has grown rapidly and proven helpful in the structure elucidation of natural products [2], [3] volatile compounds [4], [5], ozonides [6], metabolites [7], in studying reaction mechanisms [8], [9] and in absolute structure determination [10], [11]. With the success of the crystalline sponge method many researchers developed alternative crystalline sponges [12], [13].…”

Determination of the Absolute Configurations of Chiral Alkanes – An Analysis of the Available Tools

“…The crystalline sponge method has been utilized for AC determination of a variety of challenging organic compounds including small molecules with a quaternary carbon stereogenic center, [ 99 ] with planar or axial chirality, [ 100 ] and with volatile alkenes. [ 101 ] Remarkable applications for AC determination of natural products include the hydrocarbon astellifadiene ( 44 ) [ 102 ] and the pseudo‐meso compound elatenyne ( 45 ) [ 103 ] shown in Figure 12. Although the applicability to chiral alkanes has yet to be seen, the crystalline sponge method is a promising analytical technique with broad substrate scope.…”