Dipole triple

In the third order of long-range perturbation theory for a system of tluee atoms A, B and C, the leading nonadditive dispersion temi is the Axilrod-Teller-Mutd triple-dipole interaction [58, 59]... 

Hence, the same teclmiques used to calculate are also used for Cg. Note that equation (A1.5.28) has a geometrical factor whose sign depends upon the geometry, and that, unlike tlie case of the two-body dispersion interaction, the triple-dipole dispersion energy has no minus sign in front of the positive coefficient Cg. For example, for an equilateral triangle configuration the triple-dipole dispersion is repulsive and varies... 

The effect of the Axilrod-Teller term (also known as the triple-dipole correction) is to make the interaction energy more negative when three molecules are linear but to weaken it when the molecules form an equilateral triangle. This is because the linear arrangement enhances the correlations of the motions of the electrons, whereas the equilateral arrangement reduces it. 

In presence of one carbon-nitrogen triple bond —C—C=N In compounds with tendency to dipole formation, e.g., C=C—C=0 In aromatic compounds... 

Revised material in Section 5 includes an extensive tabulation of binary and ternary azeotropes comprising approximately 850 entries. Over 975 compounds have values listed for viscosity, dielectric constant, dipole moment, and surface tension. Whenever possible, data for viscosity and dielectric constant are provided at two temperatures to permit interpolation for intermediate temperatures and also to permit limited extrapolation of the data. The dipole moments are often listed for different physical states. Values for surface tension can be calculated over a range of temperatures from two constants that can be fitted into a linear equation. Also extensively revised and expanded are the properties of combustible mixtures in air. A table of triple points has been added. 

In order for dipole—dipole and dipole-iaduced dipole iateractioas to be effective, the molecule must coataia polar groups and/or be highly polarizable. Ease of electronic distortion is favored by the presence of aromatic groups and double or triple bonds. These groups frequently are found ia the molecular stmcture of Hquid crystal compouads. The most common nematogenic and smectogenic molecules are of the type shown ia Table 2. 

Figure 4.2. Rotational-energy barriers as a function of substitution. Tbe small barrier ( 2kcal) in ethane (a) is lowered even further ( O.Skcal) if three bonds are tied back by replacing three hydrogen atoms of a methyl group by a triple-bonded carbon, as in methylacetylene (b). The barrier is raised 4.2 kcal) when methyl groups replace the smaller hydrogen atoms, as in neopentane (c). Dipole forces raise the barrier further ( 15 kcal) in methylsuccinic acid (d) (cf. Figure 4.3). Steric hindrance is responsible for the high barrier (> 15 kcal) in the diphenyl derivative (e). (After...

Indeed, in the speetrum of ethynylpyrazole 94, the triple bond appears at 2112 em and then in the speetrum of earbinol 95, as in other disubstituted aeetylenes, their frequeney inereases by about 100 em . Note that the high intensity of the 2112 em band of eompound 94 is likely to result from the elevated eleetron density at position 4 of the pyrazole ring and the resulting inerease in the dipole moment of the triple bond eonjugate to it. 

Alkylvinylacetylenes react with 1,3-dipoles exclusively across the terminal unsubstituted bond, whether it is a double or triple bond (80UK1801). 1-Heteroalk-1-en-3-ynes behave quite differently in these reactions. Orientation is largely determined by the nature of heteroatom. 

The ynaminoketone vinylogs react with 1,3-dipoles (C,N-disubstituted nitii-limines, benzonitrile A-oxide) in a regio- and stereospecific fashion at the triple... 

A reliable calculation of polarizabilities requires an adequate description of the outer part of the electron density. For this reason Kassimi and Lin [98JPC(A)9906] used augmented basis sets of triple- quality to study polarizabilities and dipole moments of thiazoles and thiadiazoles. They expect their results to be reliable within 5%. In addition, the authors provide MP2/6-31G geometries for most of their structures. Hyperpolarizabilities for substituted thiazoles obtained from calculations at lower levels are also provided [99MI2]. 

Dickson and Becke, 1996, use a basis set free numerical approach for obtaining their LDA dipole moments, which defines the complete basis set limit. In all other investigations basis sets of at least polarized triple-zeta quality were employed. Some of these basis sets have been designed explicitly for electric field response properties, albeit in the wave function domain. In this category belong the POL basis sets designed by Sadlej and used by many authors as well as basis sets augmented by field-induced polarization (FTP) func-... 

Other interesting multicomponent sequences utilizing isocyanides have been elaborated by Nair and coworkers. In a recent example, this group exploited the nucleophilic nature of the isocyanide carbon, which allows addition to the triple bond of dimethyl acetylenedicarboxylate (DMAD) (9-90) in a Michael-type reaction (Scheme 9.19) [59]. As a result, the 1,3-dipole 9-91 is formed, which reacts with N-tosylimines as 9-92 present in the reaction vessel to give the unstable iminolactam 9-93. Subsequently, this undergoes a [1,5] hydride shift to yield the isolable aminopyrroles 9-94. In addition to N-tosylimine 9-92 and cyclohexyl isocyanide (9-89), substituted phenyl tosylimines and tert-butyl isocyanide could also be used here. 

Since Huisgen s definition of the general concepts of 1,3-dipolar cycloaddition, this class of reaction has been used extensively in organic synthesis. Nitro compounds can participate in 1,3-dipolar cycloaddition as sources of 1,3-dipoles such as nitronates or nitroxides. Because the reaction of nitrones can be compared with that of nitronates, recent development of nitrones in organic synthesis is briefly summarized. 1,3-Dipolar cycloadditions to a double bond or a triple bond lead to five-membered heterocyclic compounds (Scheme 8.12). There are many excellent reviews on 1,3-dipolar cycloaddition, in particular, the monograph by Torssell covers this topic comprehensively. This chapter describes only recent progress in this field. Many papers have appeared after the comprehensive monograph by Torssell. Here, the natural product synthesis and asymmetric 1,3-dipolar cycloaddition are emphasized.630 Synthesis of pyrrolidine and -izidine alkaloids based on cycloaddition reactions are also discussed in this chapter. 

One obvious synthetic route to isoxazoles and dihydroisoxazoles is by [3+2] cycloadditions of nitrile oxides with alkynes and alkenes, respectively. In the example elaborated by Giacomelli and coworkers shown in Scheme 6.206, nitroalkanes were converted in situ to nitrile oxides with 1.25 equivalents of the reagent 4-(4,6-di-methoxy[l,3,5]triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) and 10 mol% of N,N-dimethylaminopyridine (DMAP) as catalyst [373], In the presence of an alkene or alkyne dipolarophile (5.0 equivalents), the generated nitrile oxide 1,3-dipoles undergo cycloaddition with the double or triple bond, respectively, thereby furnishing 4,5-dihydroisoxazoles or isoxazoles. For these reactions, open-vessel microwave conditions were chosen and full conversion with very high isolated yields of products was achieved within 3 min at 80 °C. The reactions could also be carried out utilizing a resin-bound alkyne [373]. For a related example, see [477]. 

Cycloaddition at C=C Bonds Cycloaddition of nitrile oxides to triple carbon-carbon bonds is a rather trivial reaction. Therefore, most attention is to new types of dipoles and dipolarophiles as well as to unusual reaction routes... 

There are several, separate types of interaction in III both covalent bonds and dipoles. Induced dipoles involve a partial charge, which we called <5+ or S, but, by contrast, covalent bonds involve whole numbers of electrons. A normal covalent bond, such as that between a hydrogen atom and one of the carbon atoms in the backbone of III, requires two electrons. A double bond consists simply of two covalent bonds, so four electrons are shared. Six electrons are incorporated in each of the rare instances of a covalent triple bond . A few quadruple bonds occur in organometallic chemistry, but we will ignore them here. 

After the N, C-labelled NBD peptide was obtained, the triple-resonance experiment developed to measure rNHC dipole-CSA CCR-rates [41] was performed as a 2-dimensional experiment. The spectra are obtained by applying a pulse sequence that was developed by Kay and co-workers [41] to measure /nhc with increased sensitivity. The experiment is one of the sensitive triple-resonance experiments, and is therefore suitable to test the feasibihty of CCR measurements and to optimize sample conditions. The pulse sequence is derived from an HNCOCA and the double and zero-quantum co-... 

A suitable CCR-rate to determine the backbone torsion angle 0 by CCR is the /NHCHcf dipole-dipole CCR-rate that conveniently can be measured by an HNCA-derived experiment [44]. Alternatively, like for the torsion angle 0, the FcuaCii-i) dipole-CSA CCR can be measured by a triple-resonance experiment that is derived from a combination of HNCA and HNCO experiments [45]. Also, CCR experiments for which the rate depends on 0 and

dipole-dipole CCR experiment can be used [46]. Unfortunately for the peptide under investigation, we were not able to successfully record any of these spectra, possibly due to the relatively strong auto relaxation. 

Substituted 1,2,3-triazolium-l-aminide 1,3-dipoles (382) react with aryl isothiocyanates at both the N=C (path a) and C=S (path b) sites to give mixtures of substituted imidazolo[4,5-fi(][l,2,3]triazoles (383) and new thiazolo[4,5-fi(][l,2,3]-triazoles (384) including tricyclic derivatives with the C(3a) and C(6a) bridgeheads linked via (CH2)4 and phenanthro groups (Scheme 50). The product distribution is controlled by the para-substituent of the aryl isothiocyanate. Theoretical calculations at the 3-210 and 6-3IG levels suggest that linear triple-bonded canonical forms of the aryl isothiocyanate system play a key role in the ambident reactivity of these systems. 

Figure 4.11. Triple-layer model (Grahame) IHP, inner Helmholtz plane OHP, outer Helmholtz plane (, water dipole +, positive end of the dipole).

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