Ring effect

Heats of formation can be estimated with reasonable accuracy by additivity of group increments and corrections for ring effects. 

Compare atomic charges and electrostatic potential maps for the three cations. For each, is the charge localized or delocalized Is it associated with an empty a-type or Tt-type orbital Examine the lowest-unoccupied molecular orbital (LUMO) of each cation. Draw all of the resonance contributors needed for a complete description of each cation. Assign the hybridization of the C" atom, and describe how each orbital on this atom is utilized (o bond, n bond, empty). How do you explain the benzene ring effects that you observe ... 

A modification of this method, related to the Beckmann rearrangement, entails treatment of a ketoxime with one equivalent of CDI, then four to five equivalents of a reactive halide such as allyl bromide or methyl iodide (R3X) under reflux in acetonitrile for 0.5-1.5 h. Quatemization of the imidazole ring effectively promotes the reaction by increasing the electron-withdrawing effect. The target amides then are obtained by hydrolysis. High yields, neutral conditions, and a very simple procedure make this modification of the synthesis of amides by azolides a very useful alternative. 1243... 

Chlorobenzene and nitrobenzene may be expected to be somewhat poorer -electron donors, but the ring effect should still be present and... 

This seemingly anomalous result, called the ring effect, has been investigated in more detail (20, 32). With a potential expression as simple as that for a single Lennard-Jones particle as the sorbate, it is possible to vary systematically the size (rrgucst -guest) or interaction (egues, hosi) parameters, as... 

The concept of the ring effect has recently been applied to the diffusion of a binary mixture of Lennard-Jones particles in zeolite NaY (57). The first particle was varied in size while the second was held fixed. The results suggest that when the diameter of the larger sorbate is close to that of the 12-ring window in zeolite NaY, the larger sorbate will diffuse faster than the smaller one. 

Calculation results at 177 K led to the prediction that methane diffuses from one a-cage to another at a rate of 1.9 x 1010 per sorbate per second in NaY zeolite and 24.3 x 1010 per sorbate per second in NaCaA zeolite. Thus, this is another example of a guest diffusing faster through a host with smaller pore windows (the so-called ring effect ), a phenomenon that had been observed previously only for noble gas atoms. 

Table VI shows that regardless of the starting isomeric olefin, selectivity is lower with Co2(CO)8 than with rhodium this is especially true when the starting isomer is conjugated. Moreover, when hydroformylation is done with Co2(CO)8, two aromatic ring effects are observed ...

When rhodium is used, this ring effect is very important only with trans-propenylbenzene, and it becomes even more important when tri-phenylphosphine is added to rhodium. 

In the presence of Co2(CO)8, selectivity seems to depend on the number and relative position of the double bond substituents as well as on the reaction temperature. As is usually the case with Co2(CO)8, hydro-formylation leads mainly to the least branched aldehydes when the carbon a to the ring bears two substituents. However, when this carbon is monosubstituted, the ring effect becomes more important and CO insertion occurs on the benzylic position. 

The value of 10 is determined by molecular and particulate (cloud and aerosol) scattering, and surface reflection. A small fraction of the molecular scattering is the non-conservative Rotational Raman scattering (RRS) that partially fills the solar Fraunhofer lines in the scattered radiation, creating what is commonly known as the Ring effect [15] As a result, the ratio Iq/F, where F is the extraterrestrial solar flux, contains structure that is correlated with solar Fraunhofer lines. By separating these effects, one can write... 

Joiner, J., Bhartia, P.K., Cebu la, R.P., Hilsenrath, E McPeters, R.D., and Park, H. (1995) Rotational-Raman Scattering (Ring Effect) in Satellite Backscatter Ultraviolet Measurements, Appl. Opt., 34, pp. 4513-4525. 

E. B. Bagley and D. D. Christianson, Uniaxial Compression of Viscoelastic Rings - Effect of Friction at the Platen Sample Interaction for Gels and Doughs, J. Rheol., 32(6), 555-573, (1988). 

The basicity of these indicators can be controlled by suitable substitution of the phenyl rings effecting ionization of the corresponding benzydrols [Eq. (1.29)]. The protonation equilibria [Eq. (1.30)] is measurable by 1H or 13C NMR spectroscopy. 

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