1.2.4- Oxadiazoles dipole moments

Oxadiazole Dipole moment (Debye units) Method... 

A study of the effect of substitution patterns in oxadiazoles and isoxazoles and their effect on the UV spectra in the lO -lO M concentration range was performed. Hypso-chromic effects and deviations from Beer s law were observed and were believed to be associated with antiparallel, sandwich-type self-association via dipole-dipole interactions. Beer s law is followed when the molecular dipole moments are small or when self-association is sterically hindered. 

Oxadiazole, 5-ethyl-3-phenyl-dipole moment, 6, 379 (77JOC1555)... 

Oxadiazoles, 6, 365-391 aldol condensation, 6, 383 bond lengths, 6, 378 catalytic hydrogenation, 5, 75 chemotherapy, 6, 391 dipole moments, 6, 378 electron densities, 6, 378 electrophilic substitution, 6, 382 ethers... 

A comparison of MP2/6-31G structural parameters of 1,2-oxazole 19 (isox-azole) and 1,3-oxazole 20 with microwave data is provided by Kassimi et al. (Scheme 16) [96JPC8752]. The general agreement is excellent. The same authors investigated dipole moments, quadrupole moments, octopole moments, and dipole polarizabilities of 19 and 20 together with several oxadiazoles and oxatriazoles [96JPC8752, 99JPC(A) 10009]. For the mean polarizability of these species, they found the approximative formula... 

The dipole moments of both 3- and 4-phenylsydnones containing dimethylamino and nitro substituents were calculated (ah initio 3-21G basis set) the magnitude increases with the electron donor attached to the phenyl ring <1995JPC1923>. Quadrupole moments, octopole moments, and polarizability of 1,2,3-oxadiazole have been determined by ab initio calculations and simple models <1996JPC8752, 1999JPC10009>. 

Ab initio electron correlated calculations of the equilibrium geometries, dipole moments, and static dipole polarizabilities were reported for oxadiazoles <1996JPC8752>. The various measures of delocalization in the five-membered heteroaromatic compounds were obtained from MO calculations at the HF/6-31G level and the application of natural bond orbital analysis and natural resonance theory. The hydrogen transfer and aromatic energies of these compounds were also calculated. These were compared to the relative ranking of aromaticity reported by J. P. Bean from a principal component analysis of other measures of aromaticity <1998JOC2497>. 

Various theoretical methods (self-consistent field molecular orbital (SCF-MO) modified neglect of diatomic overlap (MNDO), complete neglect of differential overlap (CNDO/2), intermediate neglect of differential overlap/screened approximation (INDO/S), and STO-3G ab initio) have been used to calculate the electron distribution, structural parameters, dipole moments, ionization potentials, and data relating to ultraviolet (UV), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), photoelectron (PE), and microwave spectra of 1,3,4-oxadiazole and its derivatives <1984CHEC(6)427, 1996CHEC-II(4)268>. 

Binary molecular co-crystals of 2,5-bis(3-pyridyl)-l,3,4-oxadiazole and 2,5-bis-(4-pyridyl)-l,3,4-oxadiazole with benzene-1,3,5-tricarboxylic and benzene-1,2,4,5-tetracarboxylic acids were studied by X-ray and thermogravimetric analysis of mass loss <2005MI1247>. Dipole moments were used to study the flexoelectric effect in guest-host mixtures of 2,5-(4-pentylbenzene)-l,3,4-oxadiazole with commercial liquid crystal hosts <2005CM6354>. The luminescence properties of many other copolymers were also investigated (see Section 5.06.12.3). 

A series of model nematic liquid crystals (among them oxadiazole derivatives) with transverse dipole moments were used to study the flexoelectric effect in guest-host mixtures with a commercial liquid crystal host <2005CM6354>. 

The l,3,4-oxadiazole-2-thione (156, R = Me, R = Ph) has a dipole moment of 9.10 D, which obviously supports its meso-ionic formulation. " The meso-ionic l,3,4-oxadiazole-2-thiones (156) form methiodides (157) which are easily hydrolyzed, yielding the acyclic esters (160a). The meso-ionic l,3,4-oxadiazole-2-thione (156, R = Me, R ... 

Sheridan and co-workers144 took the microwave spectra of oxadiazole after its synthesis in 1962.39 From an analysis of Stark effects for a number of transitions, they concluded that the dipole moment should be 1.2 0.3 D (Table II). Davies and Mackrodt139 calculated the dipole moment to be 1.34 D, within the experimental error of Sheridan s value, by the CNDO/2 method of Pople and Segal. Other calculations133,136,138 indicate that the dipole moment of 1,2,4-oxadiazole should be notably less than that of the 1,2,5- and 1,3,4-isomers. Direct measurements of dipole moments by Milone145 had portended this much earlier. Besides the ones given in Table II, Milone had also found the same range of dipole moments for 3-methyl-5-phenyl, 5-methyl-3-phenyl, and other derivatives of the three sets of isomeric oxadiazoles. 

The structure of 1,2,4-oxadiazoles has not been in dispute since covalent structures can be drawn from the methods of synthesis. The geometry of the ring was estimated for theoretical calculations years before X-ray measurements were available. Microwave spectra and recently fluorescence spectra have been used to determine the dipole moments of oxadiazoles and oxadiazolines, the latter being high by comparison (Table 7). Electron densities were calculated for 5-methyl-3-phenyl-l,2,4-oxadiazole (88) and its 2,3-dihydro derivative (89) (77JOC1555). 

Bond lengths and angles, dipole moments (Table 2, Section 4.01.3.2) and 14N nuclear coupling have been determined and the 14N hyperfine structure has been analyzed for several 1,3,4-oxadiazoles (74PMH(6)53). Observed 44N quadrupole coupling constants have been compared with values obtained from microwave spectra (74JCP(6l)l494). 

PE spectra of 1,3,4-oxadiazolidines (Section 4.23.2.3), 1,3,4-oxadiazole and A3-l,3,4-oxadiazoIin-2-ones (Section 4.23.2.1) have been recorded. X-Ray diffraction data are available for several substituted 1,3,4-oxadiazoles and dipole moments have been measured <62HC( 17)263). 

Young and Fitzgerald (1995) analyzed the effects of dipole moments on the hole mobilities of a series of aiylalkane, aiylamine, carbazole, hydrazone, pyrazoline, and oxadiazole molecules doped into a PC, PS, and as vapor-deposited glasses. The results agreed with earlier work of Sugiuchi et al. (1991). With the exception of the aiylalkane derivatives, the mobilities decreased in a near exponential manner with increasing dipole moment. 

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