Intramolecular 1,3 separations

In some molecular geometries, the so-called intramolecular 1,3 separations are remarkably constant. The 1,3 label refers to the interactions between two atoms in the molecule which are separated by a third atom. The near equality of the nonbonded distances in the ONF3 molecule is a special case. What is more commonly observed is the constancy of a certain 1,3 nonbonded distance throughout a series of related molecules. Significantly, this constancy of 1,3-distances may be accompanied by considerable changes in the bond lengths... 

In some molecular geometries, the so-called intramolecular 1,3 separations are remarkably constant. The 1,3 label refers to the interactions between two atoms in the molecule which are separated by a third atom. The... 

Right Histograms of the olg(3II) population vs the iodine-iodine separation at 2 time points. Shown are the first two exits for such points in time that the dissociative population has reached an average intramolecular separation of —4 A (This distance is about the upper limit of the experimental probing window.) [16] The localized nature of the dissociative population is a direct result of the vibrational localization on the parent 6 state, as an exit to the a state occurs only when there is population in the curve-crossing region. 

It has been suggested that alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions (124-126). Clear spectroscopic evidence for n interactions stems from investigations of alkenylaluminum compounds having a suitable intramolecular separation between the aluminum center and the double bond (127). IR and NMR data of these compounds show comparably lower alkene stretching frequencies and deshielded vinylic protons. Furthermore, these molecules are monomeric in solution this indicates that the tendency toward 7i-complex formation is stronger than that toward the dimeric bonding usual in aluminum alkyls. 

According to the Norrish reaction of the II type there occurs intramolecular separation of the hydrogen atom and formation of the radical with its following decay [238]. 

One of the chlorine atoms in phosphorus pentachloride appears to hold a unique position in that the products of the reaction mth indene, styrene, a-methylstyrene and 5 u.-diphenylethylene m cold benzene solution, suffer hydrolysis accompanied by intramolecular separation of the fifth chlorine atom as hydrogen chloride when treated with water. At much higher temperatures certain indones add on two chlorine atoms when treated with phosphorus pentachloride, this decisively indicating the fission PCI5 PClg + Clg. 

The quenching interactions in these peptide structures are occurring in the presence of conformational flnctuations which lead not only to large changes in the intramolecular separations of Dye-Trp, but also in the electrostatic interactions of Arg+with the dye and side chain polarizations. In the presence of spatial fluctuations. 

FIG. 8. The potential energy per atom, E E Qy of molecule No. 7 before and after dissociation as a function of the intramolecular separation After dissociation, E and are those associated with the fragments of the molecule.. 391e is the average potential energy of the system... 

Modified DID model. As seen from Eq. (4.1.5) for some cases the simple dipole-induced-dipole (DID) model formulated by Silberstein for a system of n interacting atoms [63], being a little modified [50] for the molecular complexes, can be effective applied. In the modified model, like for the dipole moment, every molecule in a complex is represented as a set of effective atoms whose polarizability depends on the intemuclear separations in the molecule. The polarizabilities of the effective atoms are chosen so that their total polarizabihty equals to the polarizability of the molecule formed by these atoms, and the interaction between the effective atoms is absent. The concept of effective atoms allows one to take into account the dependence of the polarizability of a complex on the intramolecular separation r and, because the small interatomic separations are excluded from calculation procedure, the use of usual DID model is appeared. 

Gumylphenol. -Cumylphenol (PGP) or 4-(1-methyl-l-phenylethyl)phenol is produced by the alkylation of phenol with a-methylstyrene under acid catalysis. a-Methylstyrene is a by-product from the production of phenol via the cumene oxidation process. The principal by-products from the production of 4-cumylphenol result from the dimerization and intramolecular alkylation of a-methylstyrene to yield substituted indanes. 4-Cumylphenol [599-64-4] is purified by either fractional distillation or crystallization from a suitable solvent. Purification by crystallization results in the easy separation of the substituted indanes from the product and yields a soHd material which is packaged in plastic or paper bags (20 kg net weight). Purification of 4-cumylphenol by fractional distillation yields a product which is almost totally free of any dicumylphenol. The molten product resulting from purification by distillation can be flaked to yield a soHd form however, the soHd form of 4-cumylphenol sinters severely over time. PGP is best stored and transported as a molten material. 

The reaction is illustrated by the intramolecular cycloaddition of the nitrilimine (374) with the alkenic double bond separated from the dipole by three methylene units. The nitrilimine (374) was generated photochemically from the corresponding tetrazole (373) and the pyrrolidino[l,2-6]pyrazoline (375) was obtained in high yield 82JOC4256). Applications of a variety of these reactions will be found in Chapter 4.36. Other aspects of intramolecular 1,3-dipolar cycloadditions leading to complex, fused systems, especially when the 1,3-dipole and the dipolarophile are substituted into a benzene ring in the ortho positions, have been described (76AG(E)123). 

The intramolecular nature of the rearrangement was firmly established by a crossover experiment in which 39 and 40 were heated simultaneously and found to yield the same products as when they were heated separately. There was no evidence for the formation of... 

Stereochemical positioning of a functional group, relative to a separate enamine moiety in the same molecule, can be done in such a manner that a simple intramolecular alkylation or acylation will cause cyclization. Such intramolecular cycloalkylations with alkyl halides have been reported 107,108). Inftamolecular cycloacylations of enamines with esters 109, 110,110a) and with nitriles 110a,l 11,111a) have also been observed. 

Any doubt about the existence of individual tautomers is now long past some tautomers can be crystallized separately (desmotropy), and others can be observed simultaneously in the same crystal (Section V,D,2) in summary, tautomers are not intrinsically different from isomers. Maybe it is worth mentioning that even two identical tautomers can differ. This is the case for the two intramolecular hydrogen-bonded (IMHB) enol tautomers of acetylacetone and for many NH-azoles they correspond to a doublewell profile for the proton transfer with both wells having the same energy (autotrope). 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

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