Naphthalene crystal structure

Figure 8.50 A comparison of the performance of atom-atom potentials using the UNI method80 and PIXEL potentials in the description of the energy landscape for 133 naphthalene crystal structures. The experimental crystal structure is represented by a cluster of 5 points representing very similar structures with different unit cell settings. Energies are given on the abscissa in kj mol 1. The plot shows the usual way of representing the results of crystal structure calculations with the expectation that the most stable structure should be at the lowest energy and exhibit the highest density. (Reproduced with permission from The Royal Society of Chemistry).

The NMR spectrum of this compound shows a diamagnetic ring current of the type expected in an aromatic system. X-ray crystal structures of 1 and its carboxylic acid derivative 2 are shown in Fig. 9.2. Both reveal a pattern of bond lengths very similar to that in naphthalene (see p. 534). ... 

In contrast to 1, the related pure host 7 may be obtained in crystalline form 68). The crystal structure of 7 is built via helical chains of alternating intra- and inter-molecular H-bonding through the carboxyl functions. This structure supplies the information that the carboxyl groups are therefore already positioned in an appropriate way to facilitate analogous H-bonding in the known inclusions of 7. As discussed later (Sect. 4.2.2), these are exclusively salt-type associates and as such, intimately interact with the carboxyl groups. Hence one may infer that displacement of the carboxyl functions from position 2 in 1 to position 8 in 7 reduces the ability of inclusion formation. Similar reasons such as the solid-solubility differences observed in the classical naphthalene/chloronaphthalene systems (alpha- vs. beta-substituted derivatives, cf. Ref. 28 may also be applied here. 

As an aside, it may be noted that the crystal structure of isoquinoline was reported recently (K. Hensen, R. Mayr-Stein, M. Bolte, Isoquinoline , Acta Crystallogr., Section C, 55,1565-1567). It is disordered and isostructural to naphthalene. Clearly, the introduction of a second heteroatom into the naphthalene ring brings with it interesting consequences. 

Diederich and coworkers [10] synthesized so-called dendrophanes (Figure 13.6) containing a paracyclophane core embedded in dendritic poly(ether-amide) shells. X-ray crystal-structure analysis indicated that these dendrimers had an open cavity binding site in the center, suitable for the binding of aromatic guests. NMR and fluorescence titration experiments revealed a site specific binding between these dendrimers and 6-(p-toluidino)naphthalene-2-sulfonate (TNS) with a 1 1 association. Also, the fluorescence spectral shift of TNS, which is... 

Fig. 4. X-Ray crystal structure of vinzolidine 1-naphthalene sulfonate [coordinates from Jones et al. (40). ...

To what extent is l,6-methanocyclodeca-l,3,5,7,9-pentaene stabilized by aromaticity The X-ray crystal structure suggests a fully delocalized 7t system. The ten carbons which make up the base are very nearly coplanar and all CC bonds are intermediate in length between normal single and double linkages, just as they are in naphthalene. 

Although lithiation remains the most frequently used metalation reaction, there have been a number of new reports of direct palladation of aryloxazolines. For example, Smoliakova and co-workers prepared the dimeric palladium complex 457 by direct reaction of Pd(OAc)2 with 2-phenyloxazoline in the presence of NaOAc/ HOAc (Scheme 8.150). ° The dimeric complex 457 was converted to the monomeric triphenylphosphine complex 458 for which the X-ray crystal structure was determined. A similar reaction sequence was observed for naphthalenes. Muller... 

In the solid state, the equilibrium is in favor of the hydrido complex (III), and its crystal structure and that of the osmium(II) analog have been determined (38). Chatt also observed that, on heating the equilibrium mixture of (II) and (III), naphthalene was eliminated and the product Ru(dmpe)2 was also a tautomeric mixture. Here the tautomer-ism involves breaking and re-formation of carbon-hydrogen bonds in the methyl groups of the phosphine ligands (IV and V) ... 

A few examples in which aromatic cation radicals have been isolated as crystalline salts, actually consist of mixed valence units. For example, crystal structure analysis showed that the naphthalene radical cation (NAP) + forms a mixed valence dimer (NAPy4 in which the two components are arranged face to face in n-stacks with an interplanar separation significantly closer than van der Waals contacts. Such an intermolecular organization arises from the sponta-... 

Birks 68) has proposed that the only change between the unexcited and excited pyrene pair is a reduction in the interplanar distance from 3.53 to 3.37 A, i.e. that the pyrene excimer is not a completely eclipsed sandwich pair either in solution or in the crystal. This proposal is consistent with the observed similarity of the excimer band position for the crystal and solution environment, and with the emission of excimer fluorescence from the crystal even at 4 K. For naphthalene, the greater separation and the nonparallel structure of nearest-neighbor pairs in the crystal apparently prohibits the formation of the sandwich excimer during the naphthalene singlet monomer lifetime. Thus, no excimer fluorescence is observed from defect-free naphthalene crystals. 

Kawakubo s fluorescence results 86> for methyl- and dimethylnaphthalene solids can be similarly related to the crystal structure. Both 2-and 2,6-substituted naphthalenes retain the same close-packed layer structure as seen in naphthalene. The only effect of the methyl substitution is to increase the crystal dimension along the naphthalene long axis87 . Less is known about the crystal structures of 1- and 1,6-substituted naphthalenes, except that the 1-substituent requires a different packing pattern than naphthalene and that 1- and 1,6-substituted naphthalenes have much lower melting points than the 2-substituted naphthalenes. The absence of sandwich pairs in 2- and 2,6-substituted naphthalene crystals certainly explains the lack of excimer fluorescence in the crystal spectra. Presumably, such pairs are also absent in crystalline 1-methylnaphthylene, but they seem to be present in glassy 1-methyl-naphthalene and in 1,6-dimethylnaphthalene solid. 

Fig. 11.8 Photocatalytic oxidation of naphthalene on various kinds of Ti02 in solution. The reaction was carried out for 1 h in the mixed solution (acetonitrile-water) containing Ti02 and naphthalene. The solution was bubbled with 02. The crystal structures and surface areas are listed underneath the graph. The main crystalline structure of each Ti02 powder is denoted by A (anatase) and R (rutile).

The crystal structure of benzene itself is even more difficult, and it is only quite recently that accurate results have been obtained. The early work on naphthalene and anthracene was also inconclusive and did not at first lend any support to the idea of strictly planar molecules. The first really conclusive results were obtained for the molecule of hexamethylbenzene (Lonsdale, 1929). In the triclinic crystal structure the atoms occupy general positions, but a careful study of the intensities of the reflections, particularly those from the pronounced cleavage plane in which the molecule is found to lie, established that the molecule was planar to within narrow limits, and also that the benzene ring was a regular hexagon. Soon afterwards the more difficult structures of naphthalene and anthracene were fully analysed with the aid of absolute intensity measurements and the use of Fourier methods of analysis (Robertson, 1933a), and it was shown that the atoms were coplanar to within a few hundredths of an Angstrom unit. 

In contrast to 9,10-dihydroanthracene, 9,10-dihydro-l,2-5,6-dibenzanthracene (67) approximates closely to a planar conformation. Preliminary X-ray analysis (Iball, 1938) established that the molecule possesses a centre of symmetry and therefore that the naphthalenic portions of the molecule must be parallel. A more detailed crystal structure analysis, using two-dimensional Fourier methods, has been completed by Iball and Young (1958), who concluded that the molecule was essentially planar (the r.m.s. deviation of the carbon atoms from the mean molecular plane is 0-039 A, the maximum displacement, 0-081 A). This planar conformation has been explained by Herbstein (1959) as arising from the need to minimize the repulsion between the... 

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