Semiquantitative Considerations

The concept of size of the nitrogen lone pair was introduced in early discussions21 of conformational equilibria, and detailed discussions and cal- 

and 5 6) illustrates the differences in conformational preferences in heterocyclic and carbocyclic systems. The C—N bond length (1.47A) is less than the C—C length (1.54 A), so that the nonbonded interactions in 2 involving R and the syn axial C—H bonds should be significantly greater than in 4. The axial orientation of R in 5 is also expected to be more favorable than in 4 because one of the syn axial interactions between R and a C—H bond in 4 is replaced by a syn axial interaction between R and the nitrogen atom and its associated lone pair of electrons. 

Just as conformational behavior in cyclohexane has been explained semi-quantitatively in terms of gauche-butane interactions (cf. 3 4, R = Me), corresponding gauche-propylamine (C—C—C—N) and other interactions can be used to discuss conformational equilibria involving heteroatoms.26 

Lone-pair-lone-pair interactions are in part responsible for the conformational features of the hexahydropyridazine and related systems,12 and these are discussed in Section III,C,2. 

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From these semiquantitative considerations we conclude that competition between, on one hand, processes which eliminate concentration gradients like vertical mixing, and on the other hand, processes which produce concentration gradients like in-situ reactions and boundary fluxes, can be highly variable in time. Sometimes vertical mixing is intensive enough to warrant the box-model approach, other times we would need a model that allows us to describe spatially continuous concentration profiles. Sometimes we need a tool which could handle both situations. Such a model will be discussed next. 

It might be good enough for semiquantitative considerations, but hardly for quantitative predictions of fading of plastics and composite materials. 

When a reactor has to be scaled up from its bench scale version, a certain number of questions arise as to its ultimate type and operation. In general, several alternatives are possible. These may be retained up to a certain degree of progress of the project, but a choice will have to be made in as early a stage as possible, on the basis of qualitative or semiquantitative considerations, before considerable effort is invested into the detailed design. 

The use of reactor models as a basis for design, associated with the ever-increasing possibilities of computers. This is an aspect that will be dealt with extensively further in this chapter. To place this aspect in the right perspective, earlier stages of design in which decisions are taken on the basis of sound judgment and semiquantitative considerations will be discussed first. 

An approach to copolymerization has been advanced by Price and Alfrey which attempts to both combine resonance and polarity considerations and accomplish the data reduction strategy of the last paragraph. It should be conceded at the outset that the Price-Alfrey method is only semiquantitative in its success. Its greatest usefulness is probably in providing some orientation to a new system before launching an experimental investigation. 

Of course, Sqo Sq if the difference is significant, the hypothesis of a common point of intersection is to be rejected. Quite rigourously, the F test must not be used to judge this significance, but a semiquantitative comparison may be sufficient when the estimated experimental error 6 is taken into consideration. We can then decide whether the Arrhenius law holds within experimental error by comparing Soo/(mi-21) with 6 and whether the isokinetic relationship holds by comparing So/(ml — i— 2) with 5. ... 

The main difference between the chromatographic process carried out in the linear and the nonlinear range of the adsorption isotherm is the fact that in the latter case, due to the skewed shapes of the concentration profiles of the analytes involved, separation performance of a chromatographic system considerably drops, i.e., the number of theoretical plates (N) of a chromatographic system indisputably lowers. In these circumstances, all quantitative models, along with semiquantitative and nonquantitative rules, successfully applied to optimization of the linear adsorption TLC show a considerably worse applicability. 

Although etch rate data for a particular polymer film yielded straight-line kinetic plots, the data from one film to another for any given polymer exhibited considerable scatter this is indicated by the large standard deviations in Tables I and II. Because of the scatter, the cause of which is under investigation, the etch rate data reported here have only semiquantitative significance. 

Layers-of-protection analysis (LOPA) is a semiquantitative methodology for analyzing and assessing risk. It is typically applied after a qualitative hazards analysis has been completed, which provides the LOPA team with a listing of hazard scenarios with associated safeguards for consideration. LOPA uses simplified methods to characterize the process risk based on the frequency of occurrence and consequence severity of potential hazard scenarios. The process risk is compared to the owner/operator risk criteria. When the process risk exceeds the risk criteria, protection layers are identified that reduce the process risk to the risk criteria. 

In the following a semiquantitative argument is presented on the recovery of the hydrodynamic boundary condition from microscopic considerations. 

Thermodynamic analysis is a useful tool in understanding CVD processes but should be used with caution and careful attention to the assumptions underlying the application. Because CVD is a nonequilibrium process, the thermodynamic predictions are often only semiquantitative and mainly serve to provide insights into the process. Accurate process prediction must include chemical kinetics and transport rate considerations. 

Consideration of Surface Tool Concerns. Reasonably fast data acquisition, small probing beam size (allowing both faster sputter profiling and spatial resolution) and semiquantitative data analysis, give AES a primary role in each of these two experiments. 

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