Preliminary Cautions

Before proceeding with this inspection of our world for chirality, we need to be mindful of several issues, namely, the integrity of photographs and other pictorial representations of chiral objects, the accuracy of classification of chiral objects, and the simple statistics associated with small sample sizes. 

FIGURE 6.2. A pinhole camera obscura. In part (a) the image is projected onto a wall and traced in part (b) the image is traced from a screen. 

Vermeer and the camera obscura. One of the most popular Dutch painters of the seventeenth century was Johannes Vermeer (1632-1675). Approximately 35 paintings are attributed to this artist, and he has developed an increasingly large number of devotees due to recent books and a popular 

Finally, we need to comment on summary conclusions based on an insufficient number of observations. We will focus in this chapter on examining our world and deciding whether certain objects or events are chiral or racemic. There is a direct analogy here to seeing whether, on flipping coins, we have more heads, more tails, or equal numbers of heads and tails. If you flip two coins, for example, the probability that you will get two heads is or 25% because there are only four outcomes, which are equally probable, namely, HH, HT, TH, and TT. If you flip N coins, what is the probability that you will get N heads The formula that is used here is the probability P = So with 10 coins the probability that they will all land as heads (or tails) is (5) ° = = 0.00098 or 

If you are observing our world and you see 10 independent objects or events that could be either A or B, and they are all A, you would probably conclude that the probability of A and B occurring is not equal. 

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As indicated previously, soils can contain carbonates and bicarbonates that release carbon dioxide when treated with acid. The release of C02 can be dramatic and can cause splattering and loss of sample. A preliminary step in any acid extraction is to check the soil sample to determine if it contains carbonate or bicarbonates. If it does, particular caution must be taken in extracting the sample. Also, because the acid extractant is neutralized by the carbonate or bicarbonate, this must be taken into account in carrying out the extraction. 

Respiratory depression Although preliminary studies did not reveal respiratory depressant effects at hypnotic doses in healthy individuals, observe caution if zolpidem is prescribed to patients with compromised respiratory function, since sedative/hypnotics have the capacity to depress respiratory drive. 

Respiratory ejects Although preliminary studies did not reveal respiratory depressant effects at hypnotic doses of zaleplon in healthy subjects, observe caution if zaleplon is prescribed to patients with compromised respiratory function because sedatives/hypnotics have the capacity to depress respiratory drive. Depression As with other sedative/hypnotic drugs, administer zaleplon with caution to patients exhibiting signs or symptoms of depression. Suicidal tendencies may be present in such patients and protective measures may be required. Intentional overdosage is more common in this group of patients therefore, prescribe the least amount of the drug that is feasible for the patient at any one time. 

PM3 semi-empirical calculations furnish a solid account of the geometries of transition-metal coordination compounds. Most distances are within a few hundredths of an A of their experimental values, but large errors appear for a few compounds. PM3 can be recommended (with due caution) for preliminary structure determinations of transition-metal coordination compounds. 

For those with a history of substance abuse or intolerance to benzodiazepines and the elderly, caution must be used in controlling anxiety. In these cases, benzodiazepines may exacerbate other conditions. Preliminary reports suggest that antipsychotics such as quetiapine may alleviate symptoms of anxiety. Other strategies include use of antihistamines such as hydroxyzine and diphenhydramine. 

While conceding that much information of a preliminary nature could be obtained by knob-twiddling —as he jokingly called it—he stoutly maintained that results obtained by such methods should be treated with caution until reinforced by more tangible evidence. 

Until rigorous scale-up rules are determined, these cautionary rules are the state of the art for now. We offer a first step toward rigorous scaling rules by scaling particle surface velocities but caution that this work is only preliminary in nature. The best advice is to be cautious—understand the physics behind the problem and that statistics of the data collected. Remember that a fundamental understanding of the issues is still limited and luck is unlikely to be on your side, hence frustrating trial-and-error is still likely (and unfortunately) necessary to be employed. 

The Gilliland correlation appears to be conservative for feeds with low values of q (the thermal condition of the feed), and can be in error when there is a large difference in tray requirements above and below the feed. The principal value of the correlation appears to be for preliminary exploration of design variables which can be refined by computer calculations. Although it is often used for final design, that should be done with caution. Other possibly superior but more difficult to use correlations have been proposed and are described in standard textbooks for example, Hines and Maddox (1985). 

Wyckoff et al. (62) have provided a preliminary coordinate list of all nonhydrogen atoms in RNase-S. Along with the list is a series of notations on the quality of the map and the fit of the atomic model to the electron density contours. The following comments concerning group accessibilities are based on this coordinate list, but detailed interpretations must be made with caution in view of the uncertainties in many parts of the structure. 

Caution. Because of the danger of explosion, the reactants must undergo a preliminary heating in a temperature gradient of 400/40°C. until the bromine has completely reacted. 

Caution. As described above, a preliminary firing of the reactants in a temperature gradient of 400/40°C. is necessary in order to eliminate the possibility of an explosion. 

The work of Swain, de la Mare, and Roberts indicated that caution was necessary because of the differences in the intermediates. However, the resonance-stabilized carbonium ion (12) formed in the rate-determining step of the solvolysis offered an attractive model for the benzenium ions (13) formed in the slow step of the substitution reaction. The preliminary correlation of rate data for solvolysis of substituted phenyl-dimethylcarbinyl chlorides and aromatic substitution reactions revealed... 

Measurements of emissions of by-product POPs, such as dioxin-like compounds and HCB have been performed and preliminary estimations exist for other POPs. However, due to uncertainty in estimations, comparisons among POPs should be made with caution. Most by-product POPs are likely to be produced from similar sources, principally pyrolytic... 

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