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ABSTRACT: The microwave spectrum of linalool, an acyclic monoterpene, was recorded for the first time in the range from 9 to 16 GHz. The only conformer observed under molecular beam conditions was assigned. Fitting the rotational spectrum with two different programs treating internal rotation yielded the rotational constants A = 1.64674020(46) GHz, B = 0.68219862(16) GHz, C = 0.61875100(20) GHz, and the centrifugal distortion constants. The standard deviation of the fit was close to experimental accuracy. A-E splittings due to the internal rotation of one methyl group could be resolved and the internal rotation barrier was determined to be 400.20(64) cm(-1). The results from microwave spectroscopy were used to validate the molecular geometry obtained from quantum chemical calculations.
Physical Chemistry Chemical Physics 03/2013; · 3.57 Impact Factor
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ABSTRACT: We report on the gas-phase structure of the most abundant conformer of diisopropyl ketone, (CH3)2HC CO-CH(CH3)2, as observed by molecular beam Fourier transform microwave (MB-FTMW) spectroscopy. The gas-phase structures of five conformers of diisopropyl ketone were optimized using ab initio calculations at the MP2/6 311++G(d,p) level of theory. The nature of the stationary points was verified using harmonic frequency calculations. The only conformer observed in the supersonic jet possesses C2 symmetry and appears as an enantiomeric pair. From the microwave spectrum, a set of three highly accurate rotational constants, five centrifugal distortion constants, as well as three sextic centrifugal distortion constants were determined. The structure of the observed conformer was optimized again at different levels of theory using the HF, MP2, and B3LYP methods. The theoretical constants of the C2 conformer were subsequently validated using the experimental constants. To understand the transitions of one conformer to the others the isopropyl groups were rotated against each other. The resulting two-dimensional potential energy surface (PES) shows nicely the symmetry of the conformational landscape and also indicates the enantiomeric pairs of the conformers. The barriers to internal rotation of the methyl groups were determined to be 1052 cm-1 and 905 cm-1 at the MP2/6 311++G(d,p) and the B3LYP/6-311++G(d,p) level, respectively. In agreement with the theoretical predictions, no internal rotation patterns could be observed in the microwave spectrum.
The Journal of Physical Chemistry A 11/2012; · 2.95 Impact Factor
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ABSTRACT: Musk made to odor: A new oxy-oxonia-Cope macrocyclization to (3Z)-configured cycloalk-3-en-1-yl formates is reported, which is useful in the synthesis of unsaturated and saturated macrocyclic ketones. The synthesized structures provide new insight into the structure-odor correlation of musks, making it likely for macrocyclic and linear alicyclic musks to address the same olfactory receptors.
Chemistry 04/2012; 18(23):7010-5. · 5.93 Impact Factor
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Angewandte Chemie International Edition 06/2011; 50(24):5576-80. · 13.45 Impact Factor
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ChemPhysChem 03/2011; 12(4):761-4. · 3.41 Impact Factor
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ABSTRACT: We observed the microwave spectrum of ethyl isovalerate by molecular beam Fourier transform microwave spectroscopy. The rotational and centrifugal distortion constants of the most abundant conformer were determined. Its structure was investigated by comparison of the experimental rotational constants with those obtained by ab initio methods. In a first step, the rotational constants of various conformers were calculated at the MP2/6-311++G** level of theory. Surprisingly, no agreement with the experimental results was found. Therefore, we concluded that in the case of ethyl isovalerate more advanced quantum chemical methods are required to obtain a reliable molecular geometry. Ab initio calculations carried out at MP3/6-311++G**, MP4/6-311++G**, and CCSD/6-311++G** levels and also density functional theory calculations using the B3LYP/6-311++G** method gave similar results for the rotational constants, but they were clearly distinct from those obtained at the MP2/6-311++G** level. With use of these more advanced methods, the rotational constants of the lowest energy conformer were in good agreement with those obtained from the microwave spectrum.
The Journal of Physical Chemistry A 01/2011; 115(2):118-22. · 2.95 Impact Factor
