A Choice

If you ever begin to feel that chemistry is a difficult subject, read this chapter again. Then ask yourself, and give an honest answer Do I have trouble because the subject is difficult, or is it because I did not choose to improve my learning skills Your honest answer will tell you what to do next. A pertinent quote from an anonymous source is, Discipline is the bridge between goals and accomplishments.  

At all stages of our lives we make choices. We then live with the consequences of those choices. Choose wisely—and enjoy learning chemistry. 

States of Matter Physical and Chemical Properties and Changes Pure Substances and Mixtures 

Separation of Mixtures Elements and Compounds The Electrical Character of Matter 

Characteristics of a Chemical Change Conservation Laws and Chemical Change 

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Having made a choice of the reaction path, we need to choose a reactor type and make some assessment of the conditions in the reactor. This allows assessment of reactor performance for the chosen reaction path in order for the design to proceed. 

Despite these problems, a choice of separation system must be made and the design progressed further before it can be properly assessed. 

The penalty as a result of the constraint having been identified enables judgment as to whether it is acceptable or too expensive. If it is too expensive, there is a choice between two options ... 

FOR THE BEST IN PAPERBACKS, LOOK FOR THE A CHOICE OF PENGUINS AND PELICANS... 

In the calculation of vapor phase partial fugacities the use of an equation of state is always justified. In regard to the liquid phase fugacities, there is a choice between two paths ... 

A detailed study of the properties of the potential products is of prime technical and economic importance, because it allows the refiner to have a choice in selecting feedstocks for his different units for separation, transformation and conversion, to set their operating conditions, in order to satisfy the needs of the marketplace in the best ways possible. 

The results of the assessment are documented in an Environmental Impact Statement (EIS), which discusses the beneficial and adverse impacts considered to result from the activity. The report is one component of the information upon which the decision maker ultimately makes a choice. A final decision can be made with due regard being paid to the likely consequences of adopting a particular course of action, and where necessary by introducing appropriate monitoring programs. 

The bare foot completion, which leaves an open hole section below the previous casing, is cheap, simple and suitable for consolidated formations which have little tendency to collapse. The slotted liner s an uncemented section of casing with small intermittent slots cut along its length, which prevents the hole from collapsing, but allows no selectivity of the interval which will be produced. The cased and cemented horizontal completion does allow a choice of which intervals will be perforated and produced. None of these examples provides any effective sand exclusion it this is required a gravel pack or a pre-packed liner can be used. 

The practical implementation of cone-beam systems requires a choice of scanning geometry and of a reconstruction method. The good answers to both these questions simultaneously can hardly be obtained. 

The software contains features such as TCG- compensation, information on probe rotation, compensations for object geometry and can provide a choice of A-, B- and C-scan images while scanning. 

The use of these techniques is an important element of industrial policy since they contribute to the creation of a business friendly regulatory environment allowing the combination of measures taken for internal organisational reasons and obligations of certification without lowering the level of safety to be achieved. Wlienever possible a choice between product control and quality assurance procedures is offered to manufacturers. 

The directive will initially come into force on 29 November 1999. From that date until 28 May 2002 manufacturers have a choice between applying the pressure equipment directive or continuing with the application of the existing national legislation. From 29 May 2002 the pressure equipment directive will be obligatory throughout the European Union. 

The Web-based graphical user interface permits a choice from numerous criteria and the performance of rapid searches. This service, based on the chemistry information toolkit CACTVS, provides complex Boolean searches. Flexible substructure searches have also been implemented. Users can conduct 3D pharmacophore queries in up to 25 conformations pre-calculated for each compound. Numerous output formats as well as 2D and 3D visuaHzation options are supplied. It is possible to export search results in various forms and with choices for data contents in the exported files, for structure sets ranging in size from a single compound to the entire database. Additional information and down-loadable files (in various formats) can be obtained from this service. 

We have said that the Schroedinger equation for molecules cannot be solved exactly. This is because the exact equation is usually not separable into uncoupled equations involving only one space variable. One strategy for circumventing the problem is to make assumptions that pemiit us to write approximate forms of the Schroedinger equation for molecules that are separable. There is then a choice as to how to solve the separated equations. The Huckel method is one possibility. The self-consistent field method (Chapter 8) is another. 

Sometimes a choice between two disconnections of this sort can be made by our first criterion (a good mechanism). How would you make TM 47 ... 

Sometimes we must make a choice between two mechanistically reasonable disconnections. How about TM 114 ... 

The measurements are predicted computationally with orbital-based techniques that can compute transition dipole moments (and thus intensities) for transitions between electronic states. VCD is particularly difficult to predict due to the fact that the Born-Oppenheimer approximation is not valid for this property. Thus, there is a choice between using the wave functions computed with the Born-Oppenheimer approximation giving limited accuracy, or very computationally intensive exact computations. Further technical difficulties are encountered due to the gauge dependence of many techniques (dependence on the coordinate system origin). 

Aside of benzene the chemist has a choice in which allyl she can use. Allyl alcohol, allyl bromide or allyl chloride can be used with equal success but allyl alcohol is a nice bonus because it is easier... 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Eor multiple unsaturated bonds, the chain is so numbered as to give the lowest possible locants to the unsaturated bonds. When there is a choice in numbering, the double bonds are given the lowest locants, and the alkene is cited before the alkyne where both occur in the name. Examples ... 

Unsaturated branched acyclic hydrocarbons are named as derivatives of the chain that contains the maximum number of double and/or triple bonds. When a choice exists, priority goes in sequence to (1) the chain with the greatest number of carbon atoms and (2) the chain containing the maximum number of double bonds. 

Should there be a choice for the fundamental straight chain of a radical, that chain is selected which contains (1) the maximum number of double and triple bonds, (2) the largest number of carbon atoms, and (3) the largest number of double bonds. These are in descending priority. 

If there is a choice among heterocyclic systems, the parent compound is decided in the following order of preference ... 

If there is a choice between components of the same size containing the same number and kind of heteroatoms, choose as the base component that one with the lower numbers for the heteroatoms before fusion. When a fusion position is occupied by a heteroatom, the names of the component rings to be fused are selected to contain the heteroatom. 

Numbering of Compounds. If the rules for aliphatic chains and ring systems leave a choice, the... 

When side chains of two or more different kinds are attached to a cyclic component, only the senior side chain is named by the conjunctive method. The remaining side chains are named as prefixes. Likewise, when there is a choice of cyclic component, the senior is chosen. Benzene derivatives may be named by the conjunctive method only when two or more identical side chains are present. Trivial names for oxo carboxylic acids may be used for the acyclic component. If the cyclic and acyclic components are joined by a double bond, the locants of this bond are placed as superscripts to a Greek capital delta that is inserted between the two names. The locant for the cyclic component precedes that for the acyclic component, e.g., indene-A - -acetic acid. 

When the sequence rules permit alternatives, preference for lower-numbered locants and for inclusion in the principal chain is allotted as follows in the order stated Z over E groups and cis over trans cyclic groups. If a choice is still not attained, then the lower-numbered locant for such a preferred... 

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