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An efficient new electrophilic reagent combination of N-Halosuccinimides (NXS)/BF3-H2O is developed as BF3-H2O is more economic, easy to prepare, nonoxidizing and offers high acidity. The structural aspects of the BF3-H2O complex are investigated.

A modified mechanistic scheme is proposed in which three intermediates are involved in the electrophilic nitration of aromatics. The proposal is based on insights gained via quantum chemical calculations for the reaction of the nitronium cation with benzene.

The density functional theory calculations and the spectroscopic analysis reveal a cyclic poly(hydrogen fluoride) bridged structure for the complexes. Data indicate that the complexes are fluorinating agents having utility in hydrofluorination and bromofluorination of alkenes and fluorination of alcohols.

Issues concerning the examination of diprotonated hydrogen halides (H3X(super 2+)) and gitonic protio methyl- and dimethylhalonium dications (CH3XH2(super 2+) and (CH3)2XH(super 2+)) using density functional theory methods are discussed. Experiments on dimethylbromonium and dimethylchloronium ions reveal a lack of hydrogen/deuterium exchange, which suggests the involvement of gitonic protodimethylhalonium dications.

Research is presented describing the use of 13C NMR spectroscopy, at low temperatures, to characterize the product carbocations and caboxonium species which result when substituted versions of 1,3-propanediol are ionized in conditions which are superacidic.

Research was conducted to examine the complexes of the super Lewis acid BH4+ cation as well as neutral BH3 with CO2, COS and CS2 by the density functional theory method. Calculations at the same B3LYP/6-311+G** level suggest that complexation of CO2, COS adn CS2 with neutral BH3 results only in very weak complexes with relatively long B-O or B-S bonds. Findings provide an insight into the related studies on superacid induced ionic hydrogenation of CO2, COS and CS2 with NaBH4 to methane.

Research was conducted to attempt the preparation of various substituted cyclobutylmethyl cations and the preparation as well as the characterization of the persistent cyclobutyldicyclopropylmethylium cation. Variable-temperature NMR studies of the cation was also performed. Results indicate that primary and secondary cyclobutylmethyl cations were elusive in superacidic media even at low temperatures. It was also found that cyclobutylmethyl cations readily undergo ring expansion-rearrangement to yield the corresponding cyclopentyl cations.

Mono- and diprotonated guanidines were synthesized in superacid solutions and investigated by 1H, 13C and 15N nuclear magnetic resonance (NMR) spectroscopy. The structures, energies and NMR chemical shifts were also computed by the ab initio/IGLO/GIAO-MP2 technique. Excellent agreements were observed between experimental and computed 13C and 15N NMR chemical shifts. No persistent triprotonated guanidine was found.

Substituted benzylic mono- and dications were synthesized and studied by 1H and 13C nuclear magnetic resonance spectroscopy and DFT/IGLO computations. Combined experimental and theoretical investigations indicated that a structure is the main resonance contributor to the 2,4,6-trimethylbenzyl cation. Similar findings were also observed fro the 2,4,6-dimethyl-4-tert-butylbenzyl and 2,3,4,5,6-pentamethylbenzyl cation.

The synthesis and characterization of triazidocarbenium dinitride such as perchlorate and tetrafluoroborate at the limit of endothermicity was examined to determine their stabilities. The study utilized electronic structure calculations and vibrational spectroscopy to assign and analyze various structures. Results show that triazidocarbenium cations are highly endothermic species. Furthermore, these compounds demonstrate endothermicity rates achievable only for ionic solids.

The spectral patterns of a series of oxonium and carboxonium ions were analyzed by using IGLO, GIAO-SCF and GIAO-MP2 methods to characterize their geometries and molecular dynamics. Nuclear magnetic resonance analysis of the oxonium ions indicated the presence of a positively charged trivalent oxygen atom that was composed of an electron octet. The series of oxonium and carboxonium ions such as R3O+, R2COH+ and RC(OH)sub2sup+ also exhibited protonated carbonyl units.

Ab initio molecular orbital calculations and hydrogen/deuterium exchange experiments were utilized to investigate the protonation of ammonium ions NR+(where R=H,CH3) producing protioammonium dications HNR(sub)4(super)2+(where R=H,CH3). It was observed through 2H nuclear magnetic resonance spectroscopy that hydrogen/deuterium exchange occurred at the CH3 groups of tetramethylammonium ion N(CH3)4+ following reaction with DF:SbF5 superacid. The observed exchange secondary to the mediation of C-H protonated gitonic azonium dication CH4N(CH3)3(super)2+ was also ruled in.

Nuclear magnetic resonance spectroscopy experiments with radioactively-labelled carbon-13 and nitrogen-15 molecules indicate that the C2 symmetry of thiourea is labelled more than C2v chemical structures at 0.5 kcal/mol. Thiourea is monoprotonated in FSO3H/SO2CIF at -80 degrees centigrade to form a thiouronium ion which is seen in spectroscopy. Monoprotonated thiourea tends to form an S-protonated molecule. Other observations are made.

Hydrogen/deuterium exchange was examined by 2H-NMR spectroscopy at the CH3 groups of the long-lived alkanoyl cations CH3CH2CO+ (4), (CH3)2CHCO+ (8), and (CH3)3CCO+ (13) when treated with excess DF*-SbF5 superacid. The intermediacy of the corresponding protio(deuterio)acylium dications may be responsible for the exchanges. Under similar conditions, there was no exchange in the acetyl ion CH3CO+ (1) in DF*SbF5, but at the same time its electrophilic reactivity was greatly improved in superacids.

Ab initio molecular orbital and density functional theory computations are used to examine energies, geometries and reactivities of halomethyl cations and their protonated analogues. The superelectrophilic activation of the halomethyl cations in superacid solutions are analyzed based on the computed energies. The protonated halomethyl cations have considerable kinetic and thermodynamic stability. 13C nuclear magnetic resonance chemical shifts of selected systems are computed by IGLO method and contrasted with empirical results.

The cubyl onium ions such as cubylcarboxonium, cubylacylium, and cubylhalonium ions have a typical structure with the strained cubane C-C bonds interacting with the electron deficient centers. The reactions between FSO3H and cubanecarboxylic acids give the respective cubylcarboxonium ions. Mono- or dicubanecarbonyl chlorides react with SbF5 to produce mono- or diacylium ions, respectively. Superacidic methylating conditions lead to the stable acylic tertiary halonium ions and dimethyl cubyl-1,4-dihalonium ions.

The superacid-catalyzed condensation of benzaldehyde with benzene results in the formation of triphenylmethane. Experiments reveal that the O,C(aromatic)diprotonated dication is formed as the reaction intermediate. The IGLO-estimated 13C NMR chemical shifts of protonated benzaldehyde are consistent with experimentally determined data of superacid solutions.

The reactivity of protonated and methylated methyl ester in superacidic media involving diprotonated gitonic carboxonium dications is investigated. Protonated methyl acetate undergoes slow acyl cleavage at -78 degree celsius in FSO3H/SbF5/SO2 solution and methylated methyl acetate undergo slow methyl exchange in CD3SO3F/SbF5 solution. This suggests a new mechanistic pathway of ester cleavage involving acyl oxygen fission with superacid protolysis.

Reinvestigation of the electrophilic attack of NO+ and NOH2+ on methane using ab initio calculations shows the ambident electrophilic NO+ attacks carbon and the super electrophilic NOH2+ transfers a proton to methane. The attack of other electrophiles such as D+, CH(sub 3)(super +), C2H(sub 5)(super +), OH+ and F+ involves a 3c-2e C-H bond insertion. All electrophilic reactions of methane proceed through five coordinate carbocation intermediate. This investigation confirms the complex nature of NO+ attack and reaffirms the general electrophilic substitution mechanism.

Formation of Cram's phenonium ion involves the protonation of benzocyclobutene under superacidic stable ion conditions. Theoretical and spectroscopic studies, and comparison with appropriate models suggest the phenonium ion as a spirocyclopropylbenzenium ion, which has a 4pi cyclohexadienyl system and additional cyclopropylcarbinyl delocalization. Ionization of 2-fluoro(tetrafluoro)benzonorbornene produces the corresponding tetrafluorobenzonotricyclyl cation, and spectral studies indicate the ion as a spirocyclopropylbenzenium ion.

High level ab initio calculations help determine the energies, electronic structures and gas phase protein affinities of a series of gitonic protodiazonium and bisdiazonium dications. Ab initio studies determining energies help estimate the decomposition barrier of dications and IGLO method helps determines the NMR chemical shifts of diazonium ions, bisdiazonium and protodiazonium dications. Nitrogen electron pairs of diazonium ions undergo protonation forming superelectrophilic gitonic dications. This superactivation explains the reactivity of diazonium ions in superacids.

Hydrogen/deuterium exchange experiments on highly acidic superacids and calculations revealed the stable protio-2-propyl dicationic intermediate responsible for 2-propyl cation protonation. Protolytic activation did not require total alkane dication formation. Alkyl cation protosolvation in strongly acid systems is involved in alkyl cation superelectrophilic activation.

Poly-O-protonated of squaric, croconic, rhodizonic and oxalic acids under superacidic conditions, and the deprotonation of oxamine, were examined. The carboxonium ions produced were characterized by 13C NMR spectroscopy. 13C NMR and ab initio/IGLO study revealed that poly-O-protonated squaric acid possesses a preferred symmetrical, planar aromic structure while polyprotonated croconic and rhodizonic acids possess carboxonium type structures. Deprotonated oxalic acid and oxamine possess planar ethene dication structure.

The nature and role of oxonium, sulfonium and carboxonium dications in super-acid catalyzed reactions are investigated using the ab initio molecular orbital theory. The energies, electron structures, protein affinities and enthalpies of these dications are also examined. Findings show that the protolytic activation of oxonium, carbonium and other ions forms superelectrophiles whose reactivity surpass that of their parent ions.

Ab initio/IGLO 29Si, 13C and 1H NMR chemical shift calculations are undertaken to investigate the supposed existence of the trimethylsilyl cation. However, comparison of these data with experimental values shows that no such cation is present in solution. Attempts to synthesize cyclic aromatic and antiaromatic organosilicenium ions and halogen-bridged organosilyl cations have failed. Likewise, the NMR spectroscopic observation of trivalent trialkyl(aryl)organosilyl cations also have failed.

The density functional theory method was used at the B2LYP/cc-aug-pVTZ level to calculate the structures and energies of N62+ and N42+.

The first chiral and highly Lewis acidic silyl cationic catalyst studied by Jorgensen et al. published in the 1998 issue of the Journal of the American Chemical Society, vol. 120 was shown by density functional theory/IGLO nuclear magnetic resonance studies as not a free tertiary alkylsilicenium ion or a somewhat coordinatively stabilized silyl cation but a de facto silylated acetonitrilium ion. This ion possessed some chirality and is capable of catalyzing reported reactions with very low enantioselectivity. A silylated benzenium ion was obtained from benzene solution.

The structures and stabilities of CH(sub 5)(super 3+) and CH(sub 6)(super 4+) and their isolectronic boron analogues BH(sub 5)(super 2+) and BH(sub 6)(super 3+), respectively, were computed at the MP2/6-31G** and QCISD (T)/6-311G** levels. Computations showed that the CH(sub 6)(super 4+) tetracation does not correspond to a minimum at the levels analyzed. In contrast, the planar C2v symmetric structure 6, with two three-center two-electron bonds was observed to be a minimum for the BH(sub 5)(super 2+) dication.

The electrophilic fluorination of methane involves the use of the ionic salts N2F(+)AsF6(-) and NF4(+)AsF6(-)(SbF6(-)) as fluorinating agents. These radicals avoid the involvement of free radical reactions. The nature of ring fluorination products and the absence of side chain substitution reveal the involvement of direct electrophilic fluorination. Reactions in HF medium yield 98-92 percent relative yield with high selectivity.

The mono- and diprotonated forms of carbonic acid were studied using NMR, ab initio and IGLO calculations. The initial calculations were performed at the HF/6-31G* level to optimize the possible geometries. The lowest energy structures were optimized at the MP2/6-31G* level. The calculated data were then compared with those obtained experimentally under superacidic conditions. A good agreement was observed between the calculated and experimental results.

The ab initio/individual gauge for localized orbitals (IGLO) calculations of the C NMR chemical shifts of bicyclo(1.1.0)but-1,3-ene, bicyclo(2.1.0)pent-1 (4)-ene, bicyclo(2.2.0)hex-1(4)-ene and bicyclo(3.2.0)hept-1(5)-ene show that the obtained values are consistent with the experimental results. However, a systematic drift occurs with increasing level of strain in the bicyclic structure. Moreover, the Raman and infrared data of bicyclo(2.2.0)hex-1(4)-ene takes a D(sub 2h) geometry. Also, bicyclo(1.1.0)but-1,3-ene and bicyclo(2.1. 0)pent-1(4)-ene have been found to exhibit highly deshielded chemical shifts.

The synthetic preparation and the spectroscopic characterization of the stable beta-silyl-substituted allyl cation, 2-(1-(trimethylsilyl)-ethenyl)- 2-adamantly cation are presented. It is shown that beta-silyl substitution in allylic cations does not lead to stabilization. It instead lessens the rotational barrier due to beta-silyl stabilization and this is due to the anisotropic effect induced by the adjacent silicon.

The structures and energies of the carbocations [C.sub.4][H.sub.7.sup.+] and [C.sub.5][H.sub.9.sup.+] are calculated by using the ab initio method. The calculated [super 13]C NMR chemical shifts of nonclassical bicyclobutonium ion has agreed well with the experimental values of [C.sub.5][H.sub.9.sup.+].

Aromatic carboxylic acids are obtained in good to excellent yield essentially tree of diaryl ketones by carboxylation of aromatics with a carbon dioxide-Al(sub 2)Cl(sub 6)/Al system at moderate temperatures(20-80 degree C). In accordance with the experimental and computational results, superelectrophilic activation of carbon dioxide by aluminium chloride complexation and its reaction with aromatics is proposed as the most viable pathway for the studied carboxylations.

The effect of acidity on the rearrangement of pivalaldehyde to methyl isopropyl ketone and theoretical calculations, which helps in the mechanism of the rearrangement is reported. This procedure is done through a reactive protosolvated carboxonium ion intermediate.

Ab initio computations were performed which show that Cs symmetrical structures are the stationary points on the potential energy surfaces of PH(sub 5)(super 2+) adn AsH(sub 5)(super 2+). The optimized structure indicates that the symmetrical structures have a 3c-2e bond. On the other hand, the D3h symmetrical, C2v symmetrical and C2v symmetrical structure are located as stable minima on the potential energy surfaces of NH(sub 6)(super 3+), PH(sub 6)(super 3+) and AsH6(sub 6)(super 3+).

The preparation and NMR spectroscopic characterization of the trimethylperoxonium ion CH3OO(CH3)2+ and the study of its chemical structure through theoretical approaches were conducted. Previous attempts to obtain CH3OO(CH3)2+ ion through the methylation of CH3-OOCH3 by (CH3)2Cl+MF6-, CH3F/AsF5 and CH3FSbF5 were unsuccessful and led to the conclusion that the CH3OO(CH3)2+ ion decomposes easily when formed. However, the new experiment was successful in preparing and characterizing the CH3OO(CH3)2+ ion through the use of ab inition/IGLO/GIAO-MP2 theoretical calculations.

The compound 2,6-dimethylmesitylene-2,6-diyl dication (2) has been prepared, characterized by nuclear magnetic resonance (NMR) spectroscopy and analyzed by DFT/IGLO. Basing on NMR data, a dienylic allylic dication system (2a) seems to be the major contributor to structure 2. DFT/IGLO theoretical NMR chemical shift computations provided excellent correlation with the experimental data. The combined experimental and theoretical procedure support structure 2a wherein the dienyl and allylic cation units are insulated from each other not unlike what is theoretically computed for the related benzene dication 3.

Frequency calculations and geometric optimizations at the PM2/6-31G level were performed to study a parent heptacoordinate carbonium ion, triprotonated methane (CH7 sup 3+ ). Consequently, it was found the the C3v symmetric form of the parent heptacoordinate carbocation molecular has a trication of three 3c-2e bonds oriented in a propeller-shaped pattern. In addition, the ab initio computations revealed its highly exothermic deprotonation property and its stable minimum on the potential energy surface.

Investigations focus on the importance of, and prove the existence of protoalleane dications in solution, and offer experimental and theoretical proof in the instance of the tert-butyl cation. The protio-tert-butyl dication may be a part of the C-scrambling observed. Besides liquid superacidic systems, protosolovation can be important in solid systems, in which the acid regions are grouped. Secondary or primary alkyl chains are less stable, but more reactive electrophiles than tert-alkyl cations such as the tert-butyl cation.