Setting up reactions

It is not necessary to weigh the solid support when setting up reactions because the scale of the reaction is determined by the crown loading. 

Finally it may be added that in the earlier days of organic chemistry the use of kinetic investigations was not so widely applied as might have been desirable. The ways of setting up reaction mechanisms were merely based upon the enormous knowledge of known reactions compiled in the literature. To us the only natural way is to corroborate such suggestions by kinetic experiments. 

The concept may be taken one step further. It is often possible to set up reactions where not only the number of electron pairs is constant, but also the formal types of bonds is the same on both sides. Consider for example calculating the stability of propene by the reaction in Figure 5.5. In this case the number of C=C, C-C and C-H bonds is the same on both sides, and the reaction energy is therefore relatively easy to calculate since the electron correlation to a large extent is the same on both sides. Such reactions, which conserve both the number and types of bonds, arc called isodesmic -... 

Apply inert gas pressure to the graduated cylinder and vent the receiving flask to deliver the liquid (Fig. 6.5). See also Chapter 9 for more details on setting up reactions under inert conditions). 

TIP In some reactions a small change in the amount of water charged can have significant effects. Setting up reactions on a test-tube scale with the concentration of water varied in increments may be an easy way to assess any potential benefits of water. 

There exist other commonplace but inappropriate practices that newly employed process chemists rethink. The laboratory habits that motivate reforms pervade small-scale chemical research, appearing whenever chemists set up reactions and isolate or purify their products. Changes save time and money and lend safety and envirorunental soimdness to chemical development. Consider the following flve examples. 

The concept may be taken one step further. It is often possible to set up reactions where not only the number of electron pairs is constant, but also the formal type of bonds is the same on both sides. Consider for example calculating the stability of propene by the reaction in Figure 5.6. 

Set up reactions to determine the number of C. burnetii genome equivalents in each DNA sample. For each unknown DNA sample, make 80 pL of TaqMan Universal PCR Master Mix containing 10 pM of dotA-F and dotA-R primers, and 333 nM of dotA-probe, as per kit instmctions. Mix 10 pL of purified DNA from step 4 with Master Mix for a final volume of 90 pL. To generate a standard curve of 10 -10 dotA copies, add 10 pL of 10-fold dilutions of purified pCR2.1-TOPO DNA containing the C. burnetii dotA gene to 80 pL of Master Mix (see Note 17). To perform PCR reactions in triplicate, add 3-25 pL aliquots of the 90 pL Master... 

A rapid method for the estimation of Xeq is to set up reaction mixtures containing known concentrations of aU reactants at some ratio close to /feq, and thus bracket the equilibrium position by varying the concentration of one reactant. After the addition of enzyme to each mixture, the change in concentration of one reactant is measured, and the change is plotted against the [product]/[reactant] ratio. The change in concentration of a chosen reactant can be positive or negative and where the line in the plot crosses zero, the [product]/[reactant] ratio equals Jfeq (Fig. 2). 

New England Biolabs. 2009a. Optimizing Restriction Endonuclease Reactions [Online]. Available at http // www.neb.com/nebecomm/tech reference/restriction enzymes/setting up reaction.asp... 

We have just seen that the rate law for a first-order reaction is simpler than the rate law for a second-order reaction. It turns out to be quite easy to set up reaction conditions for a second-order reaction so that its kinetics will resemble a first-order reaction. When this is the case, we say that the reaction is pseudo first order. This situation results if we pick one of the two reactants, say A, and make its initial concentration much greater than the concentration of B. Then, we will follow the reaction experimentally only until about 1% of B has reacted. At this time, the concentration of A will scarcely have changed at all. So the rate law reduces to... 

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