The conformational landscape and ring-puckering properties of ε-caprolactone have been analyzed by using microwave spectroscopy and quantum chemical calculations. Two conformers were detected in a supersonic jet expansion, the most stable form being a chair containing the ester group in its rectangular flap. This conformation benefits from reduced CH2 bond eclipsing and angle strain, while π-el...

the 1h and natural-abundance 13c-nmr spectra of 1-thiacyclooctan-3-one (1) have been measured from 25 to -100°c. coalescence is observed in the 1h-nmr spectra of (1) at about -80°c, and attributed to ring inversion in a boat-chair conformation, which is the predominant conformation of (1). the free energy of activation (dg¹) for this process is 9.2±0.2 kcal/mol. the 13c-nmr spectra of (1) is te...

In the title compound, C11H20O8S, the furan-ose ring has a pseudorotation phase angle equal to 31.3° and assumes a (3) T 4 conformation, with deviations of 0.297 (4) and -0.152 (4) Å for the corresponding C atoms. The dioxolane ring adopts an envelope conformation. One of the O atoms is at the flap and deviates from the least-squares plane formed by the other four ring atoms by 0.405 (2) Å. The...

The P—S bond cleavage process in the hydroperoxidolysis of a model system for the nerve agent VX was studied using ab initio and semiempirical molecular orbital methods. Aqueous solvation effects were included through single-point calculations using the semiempirical SM5.2PD/A continuum solvation model and geometries optimized at the HF/MIDI! level of theory. The predominant pathway for P—S bon...

The asymmetric unit of the title compound, NH4 (+)·C11H14N6O7P(-)·0.5H2O, contains one 3'-azido-3'-de-oxy-thymidine-5'amino-carbonyl-phospho-nate (ACP-AZT) anion, half of an NH4 (+) cation lying on a twofold rotation axis and in another position, occupied with equal probabilities of 0.5, an NH4 (+) cation and a water mol-ecule. The amide group of the ACP-AZT anion is disordered (occupancy ratio...

The molybdenyl compound [NBu4][MoO2(C6F5)3] () has been obtained by low-temperature treatment of MoO2Cl2 with LiC6F5 in Et2O followed by addition of [NBu4]Br. This compound of the (AO2X3)(-) type shows an unusual five-coordinate structure not lying in the Berry-pseudorotation path: it can be described rather as an edge-capped tetrahedron (TE-5). The same kind of structure has been found by DFT ...

Between 100 kHz and 2 GHz ultrasonic attenuation spectra of disaccharides in water have been measured at 25 degrees C. Some additional measurements have been performed at different temperatures between 10 and 35 degrees C and as a function of saccharide concentration c (0.5 mol/l</=c</=1.8 mol/l). The analytical description of the spectra in terms of relaxation spectral functions revealed four ...

A definition of minimum distortion paths between two polyhedra in terms of continuous shape measures (CShM) is presented. A general analytical expression deduced for such pathways makes use of one parameter, the minimum distortion constant, that can be easily obtained through the CShM methodology and is herein tabulated for pairs of polyhedra having four to eight vertexes. The work presented he...

4-Thiouridine, Crystal Packing Forces, Molecular Structures 4-thiouridine crystallizes from butyric acid in the form of yellow needles, monoclinic space group P2 j with a = 10.136 (3), b = 4.843 (2 ), c = 11.257 (3) A, ß = 93.91 (5) °. The crystal structure was solved on the the basis of 895 X-ray counter data using direct methods and refined to a reliability index of R = 5.6%. 4-thiouridine is...