Small structure effects

Removal of the the related ethoxymethyl group from an imidazole with 6 N HCl at reflux is slow and low yielding. Small structural effects at a site seemingly remote from the MOM group can have a significant influence on the deprotection process. The MOM group in compound a is easily removed with acid, but the cleavage with HCl in compound b proved quite difficult. ... 

Chapter 2 by Laszlo Nyulaszi and Zoltan Benko deals with the chemistry and physical organic chemistry of aromatic phosphorus heterocycles and is divided into four subchapters dealing with three-, four-, five-, and six-membered rings, in which there may be more than one phosphorus atom. The chapter begins with a clear presentation of the electronic structure that phosphorus may achieve in molecules with CP bonds. For cyclopentadiene and phosphole eight aromaticity indices are collected. Almost all of them indicate that phosphole is more aromatic than cyclopentadiene. It is also shown that even small structural effects (substituent, bonding modes) can have a substantial impact on the chemistry of the reported systems. 

The X-ray crystallographic analysis of 9 provided experimental structural data of the new corannulene-type aromatic system. The bond alternation found in 9 closely follows the pattern found in an X-ray crystal structure of tetramethyl fused corannulene [38c]. Such agreement of the bond alternation patterns indicates that the fullerene framework and the dibenzo conjugation added to the parent corannulene structure have a small structural effect in spite of the rather large difference in hybridization of the carbon atoms between 9 p-orbital axis vector (POAV) angles [40] = 8.0-12.8° and C (POAV = 0.0-11.0°). 

Numerous small structural effects have also been revealed by microwave structure studies. In this section a few of these results are pointed out to provide the reader with an indication of what can be found from a study of the rotational spectrum. Also, some of the areas of study are mentioned briefly to indicate the wide range of problems being attacked by microwave spectroscopy. Many detailed structures and molecular information other than those mentioned here have been obtained, and the reader should consult the Bibliography and references cited therein for further examples. 

The followmg types of studies will not be presented individually but may have contnbuted supportmg data to coverage by compound type conformational analyses [23 24, 25, 26 27], fluoropolymers [28, 29, 30 31, 32], solid-state NMR [ii], and solvent effects [34 35, 36, 37] Many excellent articles with m-depth NMR interpretation of one specific compound or of a small, structurally related group of compounds can be found in the chemical hterature A few of these, not incorporated elsewhere in this secUon are referenced here carbonyl fluondes [JS 39 40], fluoropropanes [41 42, 43], fluorocyclopropanes [44, 45 46], fluorobutanes [47], perfluorocyclobutanone [48], fluorohexanes [49], and vinyl fluondes [50, 51 52, 53, 54]... 

IV, C, 1, d). Second, for both classes of aromatic compounds such values show a surprisingly small dependence on the nature of the attacking reagent, probably indicating the predominant role of the reorganization of the substrate toward a new state represented by structure 63 or 65. FinaUy, it may not be fortuitous that a correspondence is found between structural effects on substitution rates and on ionization constants (Section IV,C, l,a). Bond-making would in fact be the essential analogy between these phenomena [Eqs. (16) and (17)], and... 

The structural effect of alkyl groups such as methyl, ethyl, and -butyl on the Rp is small. Alkyl 4-methyl-phenylcarbamate can be chosen as a model compound for the hard segment of poly(ether-urethane) (PEU). This group can initiate grafting reaction with Ce(IV) ion and the grafting site was proposed at the hard segment of PEU [3,15] as shown in Scheme (1). 

Small-Particle Effects and Structural Considerations for Electrocatalysis Kinoshita, K. 14... 

An example of a structural effect is on the gold (111) surface where there is an in-plane tangential surface pressure (, , 35) On extended surfaces, a hill-and-valley roughening occurs to accommodate the expansion, as described earlier. In contrast, small particles accommodate the pressure by a surface buckle ( ). We would expect similar behaviour when there is chemisorption involving interactions between the adsorbed molecules. 

Kinoshita, K., Small-particle effects and structural considerations for electrocatalysis, in Modem Aspects of Electrochemistry, 1. O M. Bockris, Eds., Vol. 14, Kluwer, New York, 1982, p. 557. 

Structural Effects of Rotation Rapid rotation in a fully convective star decreases the core temperature, but actually increases Tt,cz once a radiative core has developed. The net effect on Li depletion seems to be rather small and cannot explain the dispersion of Li abundances seen among the slow rotating ZAMS stars [24]. 

Examples of the application of correlation analysis to diene and polyene data sets are considered below. Both data sets in which the diene or polyene is directly substituted and those in which a phenylene lies between the substituent and diene or polyene group have been considered. In that best of all possible worlds known only to Voltaire s Dr. Pangloss, all data sets have a sufficient number of substituents and cover a wide enough range of substituent electronic demand, steric effect and intermolecular forces to provide a clear, reliable description of structural effects on the property of interest. In the real world this is not often the case. We will therefore try to demonstrate how the maximum amount of information can be extracted from small data sets. 

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