Hydrogen homo-intermolecular

The X-ray crystal structure of the tetrabutylammonium (TBA) salt of anion 72 revealed complementary hydrogen bonds leading to homo-intermolecular diene as a building unit <2003SM669>. 

When two or more molecules of the same type associate, so-called homo-intermolecular hydrogen bonds are formed (Fig. 2-4). The association of different molecules e.g. R—O—H- -NRj) results in hetero-intermolecular hydrogen bonds. The designations homo- and heteromolecular [192] as well as homo- and heteroconjugated hydrogen bond are also in use. A remarkable example of a competitive solvent-dependent equilibrium between homo- and hetero-intermolecular hydrogen-bond associated species has been found in solutions of 4-hydroxyacetophenone and 2-(2-hexyloxyethoxy)ethanol [319]. 

An intermolecular 1,3-dipolar cycloaddition of diazocarbonyl compounds with alkynes was developed by using an InCl3-catalyzed cycloaddition in water. The reaction was found to proceed by a domino 1,3-dipolar cycloaddition-hydrogen (alkyl or aryl) migration (Eq. 12.68).146 The reaction is applicable to various a-diazocarbonyl compounds and alkynes with a carbonyl group at the neighboring position, and the success of the reaction was rationalized by decreasing the HOMO-LUMO of the reaction. 

The relationships between tautomeric equilibrium constants and intramolecular hydrogen bonds (IMHB) are well documented. As expected, an IMHB stabilizes the tautomer that presents it in comparison with other tautomers without IMHB. On the other hand, information about the effect of intermolecular hydrogen bonds on the thermodynamic aspect of tautomerism is scarce. These HBs are of paramount importance in the solid state in solution, the situation is more complicated because there are several possible associations that exist in dynamic equilibrium. For this reason we devoted a theoretical paper to this question, studying homo- and heterodimers of 2-pyridone (63, 64, 65) and 2-aminopyridines (66, 67, 68) [84], In the case of pyridone the most stable dimer is 63 for 2-aminopyridine, it depends on the nature of R. 

The ene reaction involves an alkene fragment (the ene) that removes a hydrogen from an allylic fragment, with formation of a new carbon bond, as in 666.. s with the other reactions in this chapter, reactivity and stereochemistry in the ene reaction can be explained by frontier orbital theory. The reaction proceeds via interaction of the HOMO of the alkene (ene) and the LUMO of the allylic partner (enophile), illustrated by 667 in Figure 11.23." The intermolecular reaction usually requires very high temperatures (typically 250-... 

An example of addition of vinyl cwbonium ion to allene has been discussed in the case of cyclodimerio products formed from allene and hydrogen hf des. Allenic participation may be considered a case of intermolecular addition of an electrophilic carbon to an allenic bond. The pmidcipation has been extensively investigated in the case of homo-allenic compounds of type 81 and homoallenic participation is the current term for the phenomenon. Earlier reports by Hanack and... 

Supramolecular assemblies constructed by hydrogen bonding can be viewed as having nanostructured modules at first. They are essential for the assemblies with low dimensions formed by intermolecular noncovalent interaction forces. For instance, supramolecular nanodisks and nanoboxes (zero-dimensional), supramolecular nanotubes, nanofilamentar cylinders (1-D), and two-dimensional homo- or het-ero- structural layers. These nanostructured assemblies provide advanced basic materials of nanoscale devices through bottom-up chemical methods. 

This unusual enhancement is attributed to relative rotamer populations in the two solvents. Extensive intramolecular hydrogen-bonding is observed in chloroform but intermolecular bonding to the solvent in DMSO. Consequently only in chloroform does the hydroxy-group hydrogen-bond to the cyclobutene and in DMSO reaction is facilitated by orbital interaction through space between the and orbitals. In view of the relation between rate and the difference in energy between HOMO and LUMO orbitals these results are not unexpected. 

The absorption bands in the regions of 7590 and 10000 cm-1 are expected to be much weaker than the band in the 2700-cm l region (Fig. 3C). This is because the two near-IR transitions depend largely on excitation of an electron from the HOMO-1 to the HOMO within one or the other BChl. Such excitations are forbidden because both orbitals have approximately the same inversion symmetry.12 Structural distortions or intermolecular interactions that decrease the orbital symmetry thus could strengthen these transitions. Hydrogen-bonding of the acetyl groups evidently can have such an effect (Fig. 3C). 

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