Pyridines molecular dimensions

The curves fell into two distinct groups. The top two curves characterize an all ethyl bromide derivative (PEB) and a derivative with 6.7 mol % of the pyridine groups substituted with n-dodecyl bromide and most of the remainder substituted with ethyl bromide (6.7% polysoap). These curves indicate highly extended molecular dimensions typical of normal polyelectrolyte behavior. Of the two derivatives, the 6.7% polysoap has a lower intrinsic viscosity but a larger increase of the reduced viscosity with concentration this result shows the intra- and intermolecular effects, respectively, of the hydrophobic attractions between the dodecyl groups. 

Monomethylated derivatives of 2-formylpyridine thiosemicarbazone have been synthesized to define molecular dimensions compatible with antineoplastic activity. These were the thiosemicarbazones of 3-, 4-, 5-, and 6-methylpyridine-2methylated pyridine derivatives were found to be active tumour-inhibitory agents, indicating that substitution of such alkyl groups did not interfere with biological potency. However, introduction of the methyl group in the 6 position of the pyridine ring resulted in a compound with no antineoplastic activity, suggesting an apparent intolerance to substitu-... 

Three different ZSM-5 crystal types have been studied by synchrotron infrared micro-spectroscopy, namely parent zeolite (ZSM-5-P), mildly treated zeolite (ZSM-5-MT) and severely treated zeolite (ZSM-5-ST). The goal is to compare the influence of different dealumination conditions on the molecular diffusion and reactivity of individual ZSM-5 crystals. Synchrotron-based IR micro-spectroscopy [34] was used in combination with pyridine adsorption. Pyridine, having a molecular dimension of 0.57 nm, is able to diffuse throughout the micropore system of ZSM-5 and allows the detection of all acidic sites present within the zeolite material [35]. The sorption of pyridine was introduced at room temperature and the samples were subsequently heated up to 573 K and 673 K. The Bronsted acid sites, giving rise to IR spectra of adsorbed pyridine at around 1545 cm , allow the visualization of differences in the nature and strength of the acid sites in the zeolite crystals under investigation. Fig. 4 shows the IR spectra of the adsorbed pyridine collected at room temperature, 573 K and 673 K for the ZSM-5-P, ZSM-5-MT and ZSM-5-ST crystals. 

The history of the discovery of pyridine and of the development of its structure was outlined in Chapter 1, and its general character as an aromatic compound, as shown in its geometry and stability, was discussed in Chapter 2. The molecular dimensions of three important pyridine derivatives, 2-pyridonei , 2-pyridthionei, and nicotinic acid are indicated in the skeletons (1), (2), and (3). Data are available for pyridine hydrochloride , 1-hydroxypyridinium chloride, 4-nitropyridine l-oxide and /mwj-4,4 -azo-pyridine 1,1 -dioxide. ... 

Interaction In the stabilization of the molecular lattice of these coals. This process no doubt gives rise to the formation of the ordered graphlte-llke structures detectable by X-ray diffraction (e.g. and apparently not disrupted by exposure of the coals to pyridine and their resultant swelling (20,21). Also the microscopic conformal and reversible nature of the swelling of coals by pyridine established by Brenner ( ) points to these ordered structures existing In mlcrodomalns of dimension less than 10 m. 

One of the most classic examples of chiral expression in thermotropic liquid crystals is that of the stereospecific formation of helical fibres by di-astereomers of tartaric acid derivatised either with uracil or 2,6-diacylamino pyridine (Fig. 9) [88]. Upon mixing the complementary components, which are not liquid crystals in their pure state, mesophases form which exist over very broad temperature ranges, whose magnitude depend on whether the tartaric acid core is either d, l or meso [89]. Electron microscopy studies of samples deposited from chloroform solutions showed that aggregates formed by combination of the meso compounds gave no discernable texture, while those formed by combinations of the d or l components produced fibres of a determined handedness [90]. The observation of these fibres and their dimensions makes it possible that the structural hypothesis drawn schematically in Fig. 9 is valid. This example shows elegantly the transfer of chirality from the molecular to the supramolecular level in the nanometer to micrometer regime. 

Porphyrin (see Porphyrin) molecules containing peripheral pyridine groups act as comers or 180° linkers depending on the positions of the pyridyl donor atoms. Reaction of (dppp)Pd(OTf)2 with (47) yields the molecular square (14) while a larger square (49) was obtained by employing a modified porphyrin (48) in which the two pyridine units are trans to each other (Scheme 15). The results of these reactions demonstrate that the ability of the molecular components to act as comers or linkers depends on their topologies. Bis-pyridyl-porphyrin (47) reacts with cis- and trani -(PhCN)2PdCl2 to yield the molecular squares (50) and (51), respectively, with varied dimensions. These squares have been characterized by NMR spectroscopy and mass spectrometry combined with UV-visible spectroscopy (see UV- Visible Spectroscopy) and vapor-phase osmometry. 

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