Straddle rules

It is of some interest to apply Trouton s rule (entropy of vaporization at the boiling point is a constant) to the above data. Unfortunately, boiling points are known only for nitric acid and some of the aliphatic nitrates. Their Trouton constants (AH p/Tbp) are 20.2 and ca 22.8 entropy units, respectively. Thus they straddle the normal Trouton constant of 21 eu. This observation, coupled with the observed constancy of the specific heat of vaporization, suggests that intermolecular bonding in nitrate esters may be relatively weak, or at least consistent... 

Every column must have a heading that describes the material below it. Be as succinct as possible, keep headings to two lines if possible, and use abbreviations and symbols whenever practical. Be consistent with the text and with other column headings. Define nonstandard abbreviations in table footnotes. Name the variable being measured and indicate the unit of measure after a comma, after a slash, or within enclosing marks. Use the same style within and among all tables. A unit of measure alone is not an acceptable column heading. A unit of measure under a straddle rule, as in Table 1, is acceptable. 

If a column heading applies to more than one column, use a rule below it that spans the columns to which it applies this is called a straddle rule. Below the rule, give the specific headings for each column. A column heading should not apply to the entire table information that describes all of the columns belongs in a general table footnote. 

In contrast to a fluid mixture, the quality of a solids mixture is difficult to determine because of the discontinuous nature of the particulate systems as well as the finiteness of particle and sample sizes The sample concentrations and their standard deviations can be affected by the error caused by the propensity of any component s particle or particle cluster to straddle the boundaries of the sample containing it. It follows that the measured standard deviation depends on the average concentration of the given key component as well as on the relative sample size. For a completely randomized mixture whose component particles are identical in size and density, this uncertainty can be determined mathematically. For other cases, this is much more complicated. To account for the effects of the sample number and size, the general rule is to take a sufficient number of samples from well-distributed points in representative regions of the mixture. Each sample must also contain a sufficient number of particles such a number can be determined from practical points of view. 

Thus, a rule of thumb says that valid normal coordinates must be either entirely symmetric or entirely antisymmetric over the most common symmetry operations if m and n label any two internal coordinates related by symmetry, then either Ukm = cikn or akm = —akn- This rule of thumb holds also in the construction of the coefficients of atomic orbitals in molecular orbitals (see Section 3.5). The bending mode of water straddles the mirror plane and is already symmetry-adapted if the displacements of the two hydrogen atoms are equal and in opposite directions (if the motions were in the same direction, that would be a molecular rotation, not a vibration). 

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