Aluminum nucleus

The surface of a solid may be considered as a defect of the solid. Nuclei near the surface of the solid will experience large electric field gradients due to the asymmetry of their environment. If these gradients are suflSciently large, the NMR signal of these nuclei in a polycrystalline sample will be broadened enough so as not to be detected by the instrument. The fraction F of aluminum nuclei so situated will not contribute to the observed intensity 1.1 is related to F in the following manner... 

All aluminum nuclei have charge +13 electronic units, so that 13 electrons orbit the nucleus of the neutral atom. Its electronic configuration can be abbreviated as an inner core of inert neon (a noble gas) plus three more electrons (Ne)3s23p1, which locates Al in Group IIIA of the chemical periodic table, between boron (B) and gallium (Ga). Its principal oxidation state is +3, so its oxide is A1203, a very important compound in cosmochemistry. Its chloride is A1C13. 

It is also possible to carry out three pulse electron spin echo experiments in which the second 180° pulse is essentially divided up into two 90° pulses separated by another experimentally variable time, T. If simultaneous modulation from two different nuclei is encountered it is possible to suppress one of these by carrying out a three pulse experiment and selecting an appropriate value of the first pulse separation time, t, to suppress one of the modulation frequencies. This is found to be particularly valuable in studying zeolite systems where modulations from both aluminum nuclei in the zeolite lattice and deuterium nuclei from water adsorbate molecules are encountered. 

D. E. O Reilly [23], in early Al experiments, considered the observability of surface aluminum atoms in aluminas. As summarized in Fig. 4, O Reilly obtained room-temperature data on a series of aluminas with varying surface areas and found that for an equal number of aluminum nuclei, each of the other aluminas had a weaker Al NMR signal than that observed for a-alumina. Specifically, for an equal number of spins the integrated signal was inversely proportional to the surface area of the particular alumina. O Reilly reasoned that the reduction in observed signal occurred because surface aluminum atoms... 

Fig. 24. Graph of the number of aluminum nuclei hi removed from observation as a function of the number of non-j3>phase chromium ions Net — N ) 121).

In 1934, Irene Curie JoUot, daughter of Marie and Pierre Curie, and her husband, FredericJoliot, bombarded aluminum (Al) with alpha particles and observed neutrons and a positron. The Joliots discovered that when the flow of alpha particles striking the Al was stopped, the neutron emissions stopped, but the positron emissions continned. They reasoned that the alpha particles reacted with aluminum nuclei to produce phosphorus-30 nuclei, which then decayed to produce positrons. 

Precision measurements of hyperfine structure and isotope shifts yield information on nuclear spins, quadrapole moments, and nuclear deformations. The results of these experiments allow tests of nuclear models of the spatial distribution of protons and neutrons in highly deformed nuclei [467]. In Fig. 4.8 the hyperfine spectra of different Na isotopes are depicted, which had been produced by spallation of aluminum nuclei by proton bombardment according to the reaction Al(/ , 3p,xn) Na [468] and in Fig. 4.29 the hfs of 6 isotopes of the titanium ion H+ illustrates the good signal-to-noise ratio. Such precision measurements have been performed in several laboratories for different families of isotopes [466-469]. 

Figure 2.8 A correlation diagram approximating how the MOs of the 2p levels of two Aluminum atoms form and are modified in energy as the respective Aluminum nuclei approach each other. This is extrapolated to zero interatomic distance such that they form the nuclei of Iron. Of note is the fact that aU but the 2p r MOs cross into the conduction band.

As an example, the fact that the 4fo- level (one of the levels that arises from the 2p core level on MO formation) crosses the conduction band when the two Aluminum nuclei are within 0.7 A of each other (this is almost half the equilibrium interatomic distance) suggests that a 2p electron can be left behind in the conduction band as the two atoms recede from the collision. This would then leave a 2p core hole (see Joyes 1969a, 1969b), which would then de-excite through either Auger electron emission or fluorescence. 

The isotopes Ga and Ga with natural abundances of 60.4% and 39.6%, respectively, are both suitable candidates for solid-state NMR spectroscopy. Since the quadrupole moments of these isotopes have the same order as that of the aluminum nucleus, similar NMR Une shapes can be expected for gallium and aluminum atoms incorporated at analogous framework sites. Moreover, Bradley et al. [152] found a linear relationship between the Ga and Al chemical shifts of a series of structurally analogous aliunimun and gaUiiun compoimds with exclusively oxygen in the first coordination sphere ... 

They calculated the probable reaction. An aluminum nucleus of 13 protons and 14 neutrons, capturing an alpha particle of 2 protons and 2 neutrons and immediately re-emitting 1 neutron must be converting itself into an unstable isotope of phosphorus with 15 protons and 15 neutrons (13 -I- 2 protons = 15 14 -I- 2 -1 neutrons = 15). The phosphorus then probably decayed to sihcon (14 protons, 16 neutrons). The 3-minute period was the half-life of that decay. 

The ESR stndy of NO adsorbed on H-ZSM zeohte yields gi = 1.995 and gi = 1.954. The spectra show a hyperfme stractnre dne to the interaction of the impaired electron with aluminum nucleus [79V1]. 

A1 MAS NMR Magic angle spinning nuclear magnetic resonance of the aluminum nucleus (spectroscopy)... 

One can envision a "worst case" substance of unknown structure which is amorphous, insoluble, and has as one of its principle components a quadrupolar nucleus. The alucones produced by the reaction of diethyMuminume oxide and ethylene glycol fit into diis category. Since the polymers are potential precursors for phase-specific aluminas, die primary structural concern is the relationship between the observed coordination environment present around the aluminum sites in the polymer and the corresponding ceramic (5 - 8). XRPD has shown diat the structures are amorphous there is no crystalinity within the microstructure which would diffract X-rays and (Uvulge hints related to the structure (Fig. 13). 27 1 is a relatively sensitive NMR nucleus, but the polymers are insoluble, and the aluminum nucleus is quadrupolar until recently NMR was all but useless for structural determination of these polymers (Fig. 14). 

Dechter J J, Henriksson U, Kowalewski J and Nilsson A-C 1982 Metal nucleus quadrupole coupling constants in aluminum, gallium and indium acetylacetonates J. Magn. Reson. 48 503-11... 

Ketone Synthesis. In the Friedel-Crafts ketone synthesis, an acyl group is iatroduced iato the aromatic nucleus by an acylating agent such as an acyl haUde, acid anhydride, ester, or the acid itself. Ketenes, amides, and nittiles also may be used aluminum chloride and boron ttitiuotide are the most common catalysts (see Ketones). 

Anthraquinone dyes are derived from several key compounds called dye intermediates, and the methods for preparing these key intermediates can be divided into two types (/) introduction of substituent(s) onto the anthraquinone nucleus, and (2) synthesis of an anthraquinone nucleus having the desired substituents, starting from benzene or naphthalene derivatives (nucleus synthesis). The principal reactions ate nitration and sulfonation, which are very important ia preparing a-substituted anthraquiaones by electrophilic substitution. Nucleus synthesis is important for the production of P-substituted anthraquiaones such as 2-methylanthraquiQone and 2-chloroanthraquiaone. Friedel-Crafts acylation usiag aluminum chloride is appHed for this purpose. Synthesis of quinizatia (1,4-dihydroxyanthraquiQone) is also important. 

Treatment of that intermediate with aluminum chloride leads to selective demethylation of that ether para to the carbonyl group (23). Cyclization by means of tosic acid gives the dihydronaphthalene nucleus (24). Alkylation of the phenol with N-(2-chloroethyl)pyrrolidine affords nafoxidine (25). ... 

The nucleus of an aluminum atom has a diameter of about 2 X 10-u cm. The atom has an average diameter of about 3 X 10-8 cm. Calculate the ratio of the diameters. 

Friedel-Crafts reaction org chem A substitution reaction, catalyzed by aluminum chloride in which an alkyl (R —) or an acyl (RCO —) group replaces a hydrogen atom of an aromatic nucleus to produce hydrocarbon or a ketone. fre del krafs re.ak shan ... 

This shape of the powder pattern is that predicted (5) for an 7 = nucleus in axial symmetry. This situation occurs for the Al nuclei in a-AljOs which is a hexagonal close-packed array of oxygen atoms with the aluminum atoms ordered in of the holes octahedrally coordinated with oxygen atoms. 

For estimation purposes, consider the 7-AI2O3 surface phase to be similar to the bulk structure—a cubic close-packed array of oxygen atoms with aluminum atoms in interstices. With this model there is one AF nucleus of... 

When aluminized AP composite propellant burns, a high mole fraction of aluminum oxide is produced as a combustion product, which generates visible smoke. If smoke has to be avoided, e. g. for miUtary purposes or a fireworks display, aluminum particles cannot be added as a component of an AP composite propellant In addition, a large amount of white smoke is produced even when non-aluminized AP composite propellants bum. This is because the combustion product HCl acts as a nucleus for moisture in the atmosphere and relatively large-sized water drops are formed as a fog or mist This physical process only occurs when the relative humidity in the atmosphere is above about 60%. If, however, the atmospheric temperature is below 260 K, white smoke is again formed because of the condensation of water vapor with HCl produced as combustion products. If the HCl smoke generated by AP combustion cannot be tolerated, the propellant should be replaced with a double-base propellant or the AP particles should be replaced with another... 

Attachment of the basic side chain to the phenothiazine nucleus by means of a carbonyl function apparently abolishes the usual CNS or antihistamine effects shown by most compounds in this class. The product azaclorzine instead is described as an anti anginal agent. Reduction of proline derivative 106 with lithium aluminum hydride gives the corresponding fused piperazine 107. Use of that base to alkylate the chloroamide 109, obtained from acylation of phenothiazine with 3-chloropropionyl chloride, leads to azaclorzine (110). ... 

The normal tip-sample distance in STM experiments can be obtained accurately from this experiment. In Fig. 8.8, the equilibrium distance, where the net force is zero, is taken as the origin of z. As shown for the case of aluminum, because the attractive force has a longer range than the repulsive force, the absolute equilibrium distance between the apex atom and the counterpart on the sample surface is slightly less than the sum of the atomic radii of both atoms, which is about 2 A. The normal topographic images on Si(lll) are usually taken at / =1 nA, corresponding to a distance of 3 A from the equilibrium point, or 5 A from nucleus to nucleus. 

Another example of the effect of a substituent on the course of reaction may be seen in the halogenation of benzo[A]quinolizinium ion (3) in the presence of aluminum halides. As will be seen in Section 2.10.2.2, electrophilic attack on a benzoquinolizinium salt usually occurs in the side-chain ring but at 100 °C, in the presence of aluminum halides, the halogen enters the central nucleus (Scheme 7). Details of the mechanism, including whether it is indeed ionic, are unknown, but it has been suggested (67JOC1169) that in the chlorination reaction the 6,11-dichloroacridizinium ion (IS) may be formed first and subsequently converted into the chlorobenzoquinolizinone (16) on nucleophilic attack by water. 

Miscellaneous Compounds. A saturated spirocychc pyrrohdine serves as the nucleus for a diamine that has been described as a hypohpemic agent. Treatment of the carbanion of the substituted cylcohexane carboxyhc ester (20-1) with methyl bromoacetate leads to the alkylation and formation of the diester (20-2). Saponification of the ester groups followed by reaction with acetic anhydride leads to ring closure of the succinic anhydride (20-3). Condensation with ammonia leads to the succinimide (20-4). The side chain is then added by alkylation of the anion on nitrogen with l-bromo-4-dimethylaminobutane (20-5). Reaction of this last intermediate with lithium aluminum hydride leads to the reduction of the carbonyl groups to methylene. This affords the pyrrolidine (20-6) atiprimod [22]. 

Interposing an additional carbon atom between the indazole nucleus and the acetic acid side chain provides another compound that shows anti-inflammatory activity in model systems. Reduction of the carboxylic acid in the indazole (38-1) by means of hthium aluminum hydride leads to the carbinol (38-2). Alkylation of the enolate from the alcohol with methyl 2-bromo-2-methylpropionate leads to the corresponding ether. Saponification gives the free acid and thus bindarit (38-3) [40]. 

Nitration of hydroxypropiophenone (7-1) followed by conversion of the phenol to its methyl ether by means of methyl iodide provides the intermediate (7-2) the nitro group is then reduced to the corresponding amine (7-3) by catalytic reduction. The newly introduced amine is then replaced by a nitrile group by successive conversion to the diazonium salt by means of nitrous acid followed by treatment with cuprous cyanide (7-4). Reaction with aluminum chloride removes the methyl ether to afford the ortho acylphenol (7-5). This is converted to the chromone (7-6) as above by reaction with benzoyl chloride and sodium benzoate. The nitrile is next hydrolyzed to the carboxylic acid (7-7) by means of sulfuric acid. The acid is then converted to its acid chloride by means of thionyl chloride and that treated with 2-(A -piperidyl)ethanol (7-8). There is thus obtained flavoxate (7-9) [8], a muscle relaxant whose name reflects its flavone nucleus. 

Much the same activity is retained when the nitrogen atoms in the heterocyclic nucleus are shifted around. The convergent scheme to this related compound starts with the acylation of alanine (35-1) with butyryl chloride (35-2). The thus-produced amide (35-3) is then again acylated, this time with the half-acid chloride from ethyl oxalate in the presence of DMAP and pyridine to afford the intermediate (35-4). In the second arm of the scheme, the benzonitrile (35-5) is reacted with the aluminate (35-6), itself prepared from trimethyl aluminum and ammonium chloride, to form the imidate (35-7). Treatment of this intermediate with hydrazine leads to the replacement of one of the imidate nitrogen atoms by the reagent by an addition-elimination sequence to form (35-8). Condensation of this product with (35-4) leads to the formation of the triazine (35-9). Phosphorus oxychloride then closes the second ring... 

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