Microwave spectrum of the 13C-ring-monosubstituted toluenes and structure of toluene

The microwave spectra of the four ¹³C-ring-monosubstituted toluene species were analyzed in the frequency range 18.5–40 GHz and their rotational constants calculated. From these data and previous work, a substitution structure and a least-squares structure were calculated and are discussed. The microwave structure of toluene, in good agreement with recent electron diffraction results, presents the following features: a slight elongation of the phenyl ring along the symmetry axis, a corresponding small narrowing of the ring, and a short C_ringC_methyl bond.     

What Is Bohmian Mechanics

Bohmian mechanics is a quantum theory with a clear ontology. To make clear what we mean by this, we shall proceed by recalling first what are the problems of quantum mechanics. We shall then briefly sketch the basics of Bohmian mechanics and indicate how Bohmian mechanics solves these problems and clarifies the status and the role of the quantum formalism.     

Fragmentation of 13C Labelled methylcyclohexanes under electron-impact

The methylcyclohexanes labelled with carbon-13 in the five possible positions have been synthesised and their mass spectra recorded. By comparison of these spectra with those of the corresponding deuterated molecules, it was possible to accurately determine the nature and the contribution of the various fragmentation paths. More than ninety percent of the fragment ions formed from methylcyclohexane result from the rupture, at one stage or another, of one of the C? C bonds attached to the tertiary carbon atoms. Besides the elemination of a polymethylene group from the ring, in either one or two steps, the two major fragmentation pathways involve the prior formation of a cyclohexyl or a cyclopentyl ion.     

Origin of the SN2 benzylic effect

The S N2 identity exchange reactions of the fluoride ion with benzyl fluoride and 10 para-substituted derivatives (RC6H 4CH 2F, R = CH3, OH, OCH 3, NH2, F, Cl, CCH, CN, COF, and NO2) have been investigated by both rigorous ab initio methods and carefully calibrated density functional theory. Groundbreaking focal-point computations were executed for the C6H5CH 2F + F (-) and C 6H 5CH2Cl + Cl (-) SN2 reactions at the highest possible levels of electronic structure theory, employing complete basis set (CBS) extrapolations of aug-cc-pV XZ (X = 2-5) Hartree-Fock and MP2 energies, and including higher-order electron correlation via CCSD/aug-cc-pVQZ and CCSD(T)/aug-cc-pVTZ coupled cluster wave functions. Strong linear dependences are found between the computed electrostatic potential at the reaction-center carbon atom and the effective SN2 activation energies within the series of para-substituted benzyl fluorides. An activation strain energy decomposition indicates that the SN2 reactivity of these benzylic compounds is governed by the intrinsic electrostatic interaction between the reacting fragments. The delocalization of nucleophilic charge into the aromatic ring in the SN2 transition states is quite limited and should not be considered the origin of benzylic acceleration of SN2 reactions. Our rigorous focal-point computations validate the benzylic effect by establishing SN2 barriers for (F (-), Cl (-)) identity exchange in (C6H5CH2F, C6H 5CH2Cl) that are lower than those of (CH3F, CH3Cl) by (3.8, 1.6) kcal mol (-1), in order.     

On the Classical Limit of Quantum Mechanics

Contrary to the widespread belief, the problem of the emergence of classical mechanics from quantum mechanics is still open. In spite of many results of the standard approach, it is not yet clear how to explain within standard quantum mechanics the classical motion of macroscopic bodies. In this paper, we shall formulate the classical limit as a scaling limit in terms of an adimensional parameter ε. We shall take the first steps toward a comprehensive understanding of the classical limit, analyzing special cases of classical behavior in the framework of a precise formulation of quantum mechanics called Bohmian mechanics which contains in its own structure the possibility of describing real objects in an observer-independent way.     

Bond-shift rearrangement during hydrogenolysis of neopentyl iodide on group VIII metal catalysts. An analogue of the mechanism of action of vitamin B12

The hydrogenolysis of neopentyl iodide on reduced Co or Pt dispersed on MgO support yields increasing amounts of 2-metylbutane and 2-methylbutenes in addition to neopentane, as the temperature is raised from 50 to 150°C. These results support the idea that a π-complexed half-reaction state is simultaneously involved in activation of the R---I bond and in the evident 1,2-methyl shift. This π-complex mechanism is the same as that first suggested almost a quarter of a century ago for neopentane isomerism during hydrogenolysis at 200°C on Pt catalysts. The present results also support the contention that similar π-complexes are responsible for analogous carbon skeleton rearrangement reactions mediated by coenzyme B₁₂.     

Coherent optical manipulations of the fundamental state in a single quantum dot

By means of an original all-optical experimental technique using microphotoluminescence in a waveguiding geometry, resonant coherent manipulation of quantum states in a single quantum dot becomes possible now. Resonant Rabi oscillation of the fundamental exciton state in a single quantum dot has been realized. We present the results obtained on two different kinds of samples: InAs/GaAs self-assembled quantum dots and naturally formed GaAs quantum dots by thickness fluctuations.