The smell of coffee: the carbon atom microwave structure of coffee furanone validated by quantum chemistry

The rotational spectra of coffee furanone (2-methyltetrahydrofuran-3-one) have been measured in the frequency range from 2.0 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer. Quantum chemical calculations used for the conformational analysis yielded two stable twist conformers, which were described using the Cremer-Pople notation for five-membered rings. The experimental spectrum of the more stable conformer with the methyl group in equatorial position was assigned and fitted using a rigid rotor model with centrifugal distortion corrections. The spectra of all five 13C-isotopologues could be observed in natural abundance. The carbon atom structure was experimentally deduced using Kraitchman's equations and compared with the structure calculated by quantum chemistry. Key words: rotational spectroscopy, conformational analysis, structure determination, five-membered ring. Resume : Nous mesurons les spectres de rotation du furanone de cafe (2- methyltetahydrofurane-3-un) dans le domaine 2.026.5 GHz, en utilisant un spectrometre microonde a transformee de Fourier avec jet moleculaire. Les calculs de chimie quantique utilises pour l'analyse de configuration donnent deux conformeres stables, qui sont decrits en utilisant la notation de CremerPople pour les anneaux a cinq membres. Le spectre experimental du conformere le plus stable avec le groupe methyl en position equatoriale est assigne et ajuste numeriquement au modele du rotateur rigide avec corrections de distorsions centrifuges. Les spectres des cinq isotopologues C sont observes selon les abondances isotopiques naturelles. La structure de l'atome de carbone est experimentalement deduite a l'aide de l'equation de Kraitchman et comparee avec la structure calculee en chimie quantique. [Traduit par la Redaction] Mots-cles : spectroscopie rotationnelle, analyse de configuration, determination de structure, anneau a cinq membres, 2-methyltetrahgydrofurane-3-un.
1. Introduction Coffee is a very popular drink in the daily life of millions of people in many countries as a first hot beverage in the morning. Several methods have [...]