Methylene group, interaction with

An activated methylene group interacts with an adjacent acetyloxy function when the compound is heated with acetic acid-acetic anhydride. The trimethyl-siiyl enol ethers (97 J) of 2-hydroxyacetophenones are useful precursors for the synthesis of heterocycles. They react with nitrosobenzene without external heat under oxidative conditions to form benzofuran-3-ones in one step without isolating intermediates, some of which are shown to be present by spectroscopic evidence. 

An explanation for these observances in the cases of ethanol and PEG may arise from hydrophobic interactions (i.e., methylene groups, methyl) with the unfolded state of the protein at elevated temperatures. This idea is supported by studies of the interaction of several alkylureas (methyl-, ACVdimethyl-, ethyl-, and butylureas) with the thermal unfolding of ribonuclease A, where it was shown... 

A five-line e.s.r. spectrum is recorded. Evidently, the grafted polymer on the photoirradiated cellulose had a conformation that restricted rotation about the Ca - Cg bond, so that only one of the methylene hydrogens and the freely rotating methyl group interact with the unpaired electron (17). 

While much of the efforts in osmium cluster chemistry are on synthesis and structural characterization, there have been a number of important studies on reactions in solution, particularly on isomerization reactions. The reaction between diazomethane and Os3(/u,-H)2(CO)io produces a mixture of a methyl complex Os3(/x-H)(CH3)(CO)io and a methylene complex Os3(/U.-H)2(/U.-CH2)(CO)iq. Variable-temperature NMR studies showed that these two isomers are in equilibrium and that the methyl group interacts with a second osmium center through a C-H-Os bridge. Two isomers of the substituted vinyl compound Os3(CO)gL(/U.-H) (/x-CH=CH2) are in equilibrium in solution. The position of the equilibrium depends on the size of the phosphine ligand, L. There is a similar steric effect in the equilibration of methyl and methylene tautomers of Os3(/u.-H)2(/U.-CH2)(CO)gL and Os3(/u.-H)(CH3)(CO)gL with larger ligands favoring the methylene complex. 

It turned out that p increases with increasing transition enthalpy of the SmA-N transition determined at atmospheric pressure. Pm decreases with decreasing number of methylene groups interacting within a layer. 

Different types of van der Waals interactions are observed in the complexes. Hydrogen bonds formed between the ammonium Hn atoms and the crown ether O atoms. The strongest Hj jO bonds in complexes of dibenzo-18-crown-6 ether with ammonium cation have a CE of 0.9 eV per bond [7] and bond distances of 1.8 A. The H atoms of the methylene and/or the phenyl group interact with the O atoms of ethers. The weakest interactions observed are between H atoms and phenyl groups as well as between two phenyl groups. In addition, the interactions are not always 1... 

The standard free energy can be divided up in two ways to explain the mechanism of retention. First, the portions of free energy can be allotted to specific types of molecular interaction that can occur between the solute molecules and the two phases. This approach will be considered later after the subject of molecular interactions has been discussed. The second requires that the molecule is divided into different parts and each part allotted a portion of the standard free energy. With this approach, the contributions made by different parts of the solvent molecule to retention can often be explained. This concept was suggested by Martin [4] many years ago, and can be used to relate molecular structure to solute retention. Initially, it is necessary to choose a molecular group that would be fairly ubiquitous and that could be used as the first building block to develop the correlation. The methylene group (CH2) is the... 

The methylene group carries an empty p orbital. Howr will the methyl group interact w ith this empty orbital Clearly the 7r-type orbitals of the methyl group (ttu in E, tt. in B) have the appropriate symmetry to mix with the p orbital. A typical orbital interaction diagram (for E) is shown in Fig. 37. Several conclusions emerge immediately from this diagram ... 

Instinctively it would seem that Step C would be rate controlling and the slowest. In the case of the Fischer-Tropsch reaction, one would postulate that the surface would offer more methylene groups for chain polymerization. This mechanism differs from that of Vlasenko and Uzefo-vich (4) essentially in the concept that the whole molecule interacts with the surface. Furthermore, the HCOH intermediate is wholly horizontal to the surface rather than perpendicular. 

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