{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T00:47:26Z","timestamp":1760316446327,"version":"build-2065373602"},"reference-count":40,"publisher":"Wiley","issue":"47","license":[{"start":{"date-parts":[[2012,10,2]],"date-time":"2012-10-02T00:00:00Z","timestamp":1349136000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Chemistry A European J"],"published-print":{"date-parts":[[2012,11,19]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>Determining the structure of reactive intermediates is the key to understanding reaction mechanisms. To access these structures, a method combining structural sensitivity and high time resolution is required. Here ultrafast polarization\u2010dependent two\u2010dimensional infrared (P2D\u2010IR) spectroscopy is shown to be an excellent complement to commonly used methods such as one\u2010dimensional IR and multidimensional NMR spectroscopy for investigating intermediates. P2D\u2010IR spectroscopy allows structure determination by measuring the angles between vibrational transition dipole moments. The high time resolution makes P2D\u2010IR spectroscopy an attractive method for structure determination in the presence of fast exchange and for short\u2010lived intermediates. The ubiquity of vibrations in molecules ensures broad applicability of the method, particularly in cases in which NMR spectroscopy is challenging due to a low density of active nuclei. Here we illustrate the strengths of P2D\u2010IR by determining the conformation of a Diels\u2013Alder dienophile that carries the Evans auxiliary and its conformational change induced by the complexation with the Lewis acid SnCl<jats:sub>4<\/jats:sub>, which is a catalyst for stereoselective Diels\u2013Alder reactions. We show that P2D\u2010IR in combination with DFT computations can discriminate between the various conformers of the free dienophile <jats:italic>N<\/jats:italic>\u2010crotonyloxazolidinone that have been debated before, proving antiperiplanar orientation of the carbonyl groups and s<jats:italic>\u2010cis<\/jats:italic> conformation of the crotonyl moiety. P2D\u2010IR unequivocally identifies the coordination and conformation in the catalyst\u2013substrate complex with SnCl<jats:sub>4<\/jats:sub>, even in the presence of exchange that is fast on the NMR time scale. It resolves a chelate with the carbonyl orientation flipped to synperiplanar and s<jats:italic>\u2010cis<\/jats:italic> crotonyl configuration as the main species. This work sets the stage for future studies of other catalyst\u2013substrate complexes and intermediates using a combination of P2D\u2010IR spectroscopy and DFT computations.<\/jats:p>","DOI":"10.1002\/chem.201201583","type":"journal-article","created":{"date-parts":[[2012,10,2]],"date-time":"2012-10-02T09:19:25Z","timestamp":1349169565000},"page":"14989-14995","source":"Crossref","is-referenced-by-count":10,"title":["Two\u2010Dimensional Infrared Spectroscopy Reveals the Structure of an Evans Auxiliary Derivative and Its SnCl<sub>4<\/sub> Lewis Acid Complex"],"prefix":"10.1002","volume":"18","author":[{"given":"Andreas T.","family":"Messmer","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Katharina 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