IUPAC as and tram


Now let us turn to the case of a highly reactive electrophile, where we expect an early transition state. In this case, the charge density and coefficients of the HOMO characteristic of the aromatic reactant would be expected to be major features governing the orientation of electrophilic attack. The transition state should resemble the reactants, and, according to frontier orbital theory, the electrophile should attack the position that has the largest coefficient in the HOMO. Methoxybenzene (anisole) can be taken as an example of a reactive molecule. MO calculations place the lone-pair oxygen orbital lower in energy than the aromatic n orbitals, leading to the MO diagram in Fig. 10.2. The degeneracy of the two highest-lying occupied n orbitals is lifted because the methoxy group interacts preferentially with one of them. The other has a node at the site of methoxy substitution. Figure 10.3 gives the coefficients for the two highest occupied n orbitals, as calculated by the CNDO/2 method. We see that the HOMO has its highest coefficients at the ipso, ortho, and para positions. As indicated in Fig. 10.2, the energy of this orbital is raised by its interaction with the electron-donor substituent. Figure 10.4 shows the distribution of n electrons from all the orbitals, based on STO-3G calculations, for various substituted benzenes. Those having the electron-donating substituents show increased electron density at the ortho and para positions. Both the HOMO coefficients and the total charge distribution predict preferential attack by the electrophile at the positions ortho and para to donor substituents.  [c.560]

Theorem 2 (Thm. 4.2. in [6]). Let 4> initialli have width <5(0) < 5 and let e be small enough. Moreover, assume that caustics do not appear in time interval [0,rj. Then, the semiclassical wavefunctions and-ipQc approximate the TDSCF wavefunction ip up to an error of order 5 -F e, i.e.,  [c.384]

A small tank was filled every day with sufficient raw material to last until the following day by watching the tank level and stopping the filling pump when the tank was 90% full. This worked for several years until the worker overfilled the tank. A high level trip was installed to turn off the pump automatically if the level exceeded 90 I. To the surprise of engineering staff the tank overflowed again after about a year because the worker decided to rely on the trip and stopped watching the level. The supervisor and foreman knew this, but were pleased that the worker s time was being used more productively. The engineers had assumed the worker would still be monitoring the fill level, m l a ho,lily rch.ibic shulnif niccham. in was not needed. The trip was being used as a process controller,  [c.171]

The body of statistical evidence.. . when examined in the context of our physical understanding of the climate system, now points towards a discernible human influence on global climate. Our ability to quantify the magnitude of this effect is currently limited by uncertainties in key factors, including the magnitude and patterns of longer-term natural variability and the rime-evolving paiterns of forcing by (and response to) greenhouse gases and aerosols [IPCC, 1995, p. 439],  [c.240]

Long-term vibration trends are a useful diagnostic tool. Trending techniques involve graphically comparing the total energy, which is the sum of the frequency components amplitude over some consistent, user-selected frequency range (i.e., Fmin to f iviAx)> over a long period to get a historical perspective of the vibration pattern. Plots of this sum against time (e.g., days) provide a means of quantifying the relative condition of the monitored machine (see Figure 44.24). Most predictive-maintenance systems provide automatictrending capabilities for recorded data. This is not to be confused with time-domain plots, which are instantaneous measures of total vibration amplitude plotted against time measured in seconds.  [c.727]


See pages that mention the term IUPAC as and tram : [c.541]    [c.1022]    [c.14]    [c.50]    [c.197]    [c.278]   
Carey organic chemistry (0) -- [ c.124 ]