Inductive Effects on Intramolecular Hydrogen Bond Strength: An Investigation of the Effect of an Electron-Withdrawing CF3 Group Adjacent to an Alcohol Hydrogen Bond Donor.

This combined experimental and theoretical study seeks to determine the role that inductive effects have on hydrogen bonds by an investigation into the change in intramolecular hydrogen bond strength in 2-amino-1-trifluoromethylethanol (2ATFME) relative to that in 2-aminoethanol (2AE). Toward this end, the rotational spectra of the normal, 13C, and 15N isotopologues have been measured using Fourier transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson A-reduction Hamiltonian. Structural parameters used to characterize the strength of the intramolecular hydrogen bond have been determined from the experimental structures of both 2ATFME and 2AE as well as from MP2/6-311++G(d,p) calculations. A comparison of these parameters in 2ATFME with those of 2AE indicates that the electron-withdrawing trifluoromethyl CF3 group strengthens the hydrogen bond. These include a 4% decrease in the distance between the donor and acceptor heavy atoms of the hydrogen bond, a 6% increase toward linearity of the OH···N angle, and a 23% decrease of the COH···N torsional angle toward planarity in 2ATFME relative to 2AE. This trend toward increased intramolecular hydrogen bond strength in 2ATFME is also observed within the ab initio structures.

Investigation of carbon buildup in simulations of multi-impact bombardment of Si with 20 keV C60 projectiles.

Beams of single C(+) ions are used for the incorporation of Si in the synthesis of thin films of SiC, which have a wide range of technological applications. We present a theoretical investigation of the use of C60 cluster beams to produce thin films of SiC on a Si substrate, which demonstrates that there are potential advantages to using C60(+) cluster ion beams over C(+) single ion beams. Molecular dynamics simulations of the multi-impact bombardment of Si with 20 keV normal incident C60 projectiles are performed to study the buildup of carbon and the formation of a region of Si-C mixing up to a fluence of 1.6 impacts/nm(2) (900 impacts). The active region of the Si solid is defined as the portion of target that contains almost all of the C atoms and the height ranges from 3 nm to more than 7 nm below the average surface height. The C fraction in the active region is calculated as a function of fluence, and a simple model is developed to describe the dependence of the C fraction on fluence. An analytic function from this model is fit to the data from the molecular dynamics simulations and extrapolated to predict the fluence necessary to achieve equilibrium conditions in which the C fraction is constant with fluence. The fraction of C atoms at equilibrium is predicted to be 0.19, and the fluence necessary to achieve 90% of this asymptotic maximum value is equal to 4.0 impacts/nm(2).