Slowing-down density

One can see that increase of board density slows down their deterioration by more than three times. 

These effects can be attributed mainly to the inductive nature of the chlorine atoms, which reduces the electron density at position 4 and increases polarization of the 3,4-double bond. The dual reactivity of the chloropteridines has been further confirmed by the preparation of new adducts and substitution products. The addition reaction competes successfully, in a preparative sense, with the substitution reaction, if the latter is slowed down by a low temperature and a non-polar solvent. Compounds (12) and (13) react with dry ammonia in benzene at 5 °C to yield the 3,4-adducts (IS), which were shown by IR spectroscopy to contain little or none of the corresponding substitution product. The adducts decompose slowly in air and almost instantaneously in water or ethanol to give the original chloropteridine and ammonia. Certain other amines behave similarly, forming adducts which can be stored for a few days at -20 °C. Treatment of (12) and (13) in acetone with hydrogen sulfide or toluene-a-thiol gives adducts of the same type. 

Decorative coatings of nickel plus chromium are cathodic to steel or zinc alloy substrates and with these protective systems deliberate use may be made of discontinuities in the chromium topcoat where corrosion of the underlying nickel will occur. If the number of these discontinuities in the chromium layer is greatly increased the current density at each individual corrosion site is reduced, penetration of corrosion through the thickness of the nickel layer is thus slowed down and the period of protection of the substrate metal is prolonged. 

We have seen how an —OH group can accelerate a reaction. Are there substituents that can slow down the electrophilic substitution of benzene One way to reduce the electron density in the benzene ring and to make it less attractive to elec-... 

Curve 1 in Fig. 6.9 shows the influence of constant k, (or of parameters or which are proportional to it) on the current density at constant potential for a reaction with an intermediate value of k°. Under diffusion control (low values of/) the current density increases in proportion to/ . Later, its growth slows down, and at a certain disk speed kinetic control is attained where the current density no longer depends on disk speed. The figure also shows curves for the kinetic current density 4 and the diffusion current density /. 

Eventually however, a crust of increasing thickness and density degins to appear on the surface, which, along with blocking of pores due to salt deposition, hinders evaporation of the liquid. Consequently, with increasing salt content the strength attains its maximum and then drops as the crystallization rate slows down. 

Here, r gas is the viscosity of the gas surrounding the liquid droplet and pliquid is the mass density of the liquid. Figure 17.4 shows the steady-state velocity of a water droplet in air as a function of the droplet radius. The quadratic dependence on the droplet radius gives rise to a dramatic slow down, thus making visualization of falling microdroplets practical. 

Calculations indicate that the unpaired electron density in the cation-radical of tetrathiafulvalene resides principally on sulfur, hut with the internal carbon being the site of second highest density. The product of coupling of an a-carbonyl radical to sulfur, an a-carbonyl-sulfonium salt would be destabilized by the adjacent dipoles. The transition state would be expected to mirror this, thus slowing down the C-S coupling and permitting the observed coupling to the carbon of tetrathiafulvalene. 

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