5,968 research outputs found
Path integral evaluation of the kinetic isotope effects based on the quantum instanton approximation
A general method for computing kinetic isotope effects is described. The
method uses the quantum-instanton approximation and is based on the
thermodynamic integration with respect to the mass of the isotopes and on the
path-integral Monte-Carlo evaluation of relevant thermodynamic quantities. The
central ingredients of the method are the Monte-Carlo estimators for the
logarithmic derivatives of the partition function and the delta-delta
correlation function. Several alternative estimators for these quantities are
described here and their merits are compared on the benchmark hydrogen-exchange
reaction, H+H_2->H_2+H on the Truhlar-Kuppermann potential energy surface.
Finally, a qualitative discussion of issues arising in many-dimensional systems
is provided.Comment: 11 pages, 2 figures, proceeding
Exploiting classical nucleation theory for reverse self-assembly
In this paper we introduce a new method to design interparticle interactions
to target arbitrary crystal structures via the process of self-assembly. We
show that it is possible to exploit the curvature of the crystal nucleation
free-energy barrier to sample and select optimal interparticle interactions for
self-assembly into a desired structure. We apply this method to find
interactions to target two simple crystal structures: a crystal with simple
cubic symmetry and a two-dimensional plane with square symmetry embedded in a
three-dimensional space. Finally, we discuss the potential and limits of our
method and propose a general model by which a functionally infinite number of
different interaction geometries may be constructed and to which our reverse
self-assembly method could in principle be applied.Comment: 7 pages, 6 figures. Published in the Journal of Chemical Physic
Path-integral virial estimator for reaction rate calculation based on the quantum instanton approximation
The quantum instanton approximation is a type of quantum transition state
theory that calculates the chemical reaction rate using the reactive flux
correlation function and its low order derivatives at time zero. Here we
present several path-integral estimators for the latter quantities, which
characterize the initial decay profile of the flux correlation function. As
with the internal energy or heat capacity calculation, different estimators
yield different variances (and therefore different convergence properties) in a
Monte Carlo calculation. Here we obtain a virial-type estimator by using a
coordinate scaling procedure rather than integration by parts, which allows
more computational benefits. We also consider two different methods for
treating the flux operator, i.e., local-path and global-path approaches, in
which the latter achieves a smaller variance at the cost of using second-order
potential derivatives. Numerical tests are performed for a one-dimensional
Eckart barrier and a model proton transfer reaction in a polar solvent, which
illustrates the reduced variance of the virial estimator over the corresponding
thermodynamic estimator.Comment: 23 pages, 5 figures, 1 tabl
An appraisal of predetermined costs as applied to the rectification and bottling of alcoholic beverages
Thesis (M.B.A.)--Boston Universit
SELECTIVE IODINATION USING DIARYLIODONIUM SALTS
Aryl iodides have become widely recognized as versatile synthetic intermediates, owing to aromatic iodine’s excellent ability to participate in oxidative addition reactions. Iodoarenes readily undergo a variety of synthetic transformations including metal catalyzed cross-coupling reactions, diaryliodonium chemistry, formation of organometallics through reduction or metal-halogen exchange, as well as classical SN2 type chemistry. Because a wide array of transformations are available for aryl iodides, organic molecules containing this moiety often serve as vital precursors to highly desirable pharmaceuticals.
This thesis describes a simple and selective two-step approach to the formation of aryl iodides. This method proceeds through an easily purified diaryliodonium salt intermediate, which is subsequently converted to the corresponding aryl iodide. This method is an effective and general process for the selective synthesis of a large variety of monoiodinated arenes that are difficult to access by other approaches.
Advisor: Stephen G. DiMagn
SELECTIVE IODINATION USING DIARYLIODONIUM SALTS
Aryl iodides have become widely recognized as versatile synthetic intermediates, owing to aromatic iodine’s excellent ability to participate in oxidative addition reactions. Iodoarenes readily undergo a variety of synthetic transformations including metal catalyzed cross-coupling reactions, diaryliodonium chemistry, formation of organometallics through reduction or metal-halogen exchange, as well as classical SN2 type chemistry. Because a wide array of transformations are available for aryl iodides, organic molecules containing this moiety often serve as vital precursors to highly desirable pharmaceuticals.
This thesis describes a simple and selective two-step approach to the formation of aryl iodides. This method proceeds through an easily purified diaryliodonium salt intermediate, which is subsequently converted to the corresponding aryl iodide. This method is an effective and general process for the selective synthesis of a large variety of monoiodinated arenes that are difficult to access by other approaches.
Advisor: Stephen G. DiMagn
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