John P. B. Sandall

The vibrational spectroscopy of C60H36: An experimental and theoretical study

Abstract Several samples of C 60 H 36 have been prepared by the transfer hydrogenation method and studied by infrared and Raman spectroscopy. The results are compared with published infrared spectra of C 60 H 36 samples synthesized by other techniques such as high pressure hydrogenation and zinc reduction of C 60 . Raman spectra of C 60 H 36 have not previously been reported. Based on previous data in the literature, five isomers of low-energy were selected for semiempirical quantum chemical calculations. They are one each of S 6 , T and T h symmetry and two isomers of D 3d symmetry. The calculations predict that very few IR lines will be coincident with Raman bands, even in the case of the T isomer for which t symmetry vibrations can be both infrared and Raman active, and for which the few coincident lines should be extremely weak. The interplay between theory and experiment places some strong constraints on the possible symmetries and structures of the various samples of the C 60 H 36 molecule. The results indicate that each of two samples prepared by transfer hydrogenation contains a mixture of two principal isomers, of D 3d and S 6 symmetries, the former being the major component in one, and the latter in the other, sample. The analysis also confirms a D 3d isomer as being the major component of a sample of C 60 H 36 prepared by high pressure hydrogenation and proposes the S 6 isomer as the major component of a sample prepared by zinc reduction of C 60 in aromatic solvents.

The isomer problem for fullerene derivatives: structural proposals for C70H36

Abstract Calculations are performed on the optimal structures and relative stabilities of the experimentally identified but as yet uncharacterized C70H36 molecule. A model in which addition preserves nominal aromaticity is tested against semi-empirical MNDO calculations and found to be inadequate: large aromatic regions on the surface of the C70 cage would demand planarity and, hence, imply large steric strain. A structure with isolated double bonds in the polar caps and conjugation in a cyclopentaphenyl belt is predicted to be more stable by some 300 kJ mol−1 than the nominally aromatic isomers, but the most stable structure found so far, improving by about 85 kJ mol−1 on all previously published proposals, has 17 localized double bonds, one in each polar cap and the others in three bands of five around the C70 cylinder, the low strain of their arrangement apparently outweighing the total loss of π delocalization.

Atom-efficient electrophilic aromatic nitration by dinitrogen pentoxide catalysed by zirconium(IV) 2,4-pentanedionate

An atom-efficient, non-acidic, catalytic process is described for the nitration of electron deficient arenes such as o-nitrotoluene using a dinitrogen pentoxide-zirconium(iv) 2,4-pentanedionate system in dichloromethane solvent. Kinetic studies showed the nitration process to be first-order with respect to the aromatic substrate and higher than first-order with respect to the catalyst. Addition of the catalyst at ca. 0.1-1 mol% compared with both N(2)O(5) and the organic substrate results in an increase in the first-order rate constant for nitration by a factor of approximately 5000 with a turnover number of at least 500. The orientation of the nitration products (2,4-/2,6-dinitrotoluenes) is consistent with attack of nitronium ion. The apparently high order of reaction with respect to the catalyst suggests a possible heterogeneous process.

Theoretical characterisation of C70Cl10: the rôle of 1,4-addition across hexagonal rings

Four isomeric structures of decachloro[70]fullerene are compatible with the 13C NMR spectrum and qualitative stability rules; explicit calculation at the semi-empirical level shows the most stable isomer to be that which maximises the number of 1,4-chlorine additions whilst excluding double bonds from pentagons.

C60F18O the first characterised intramolecular fullerene ether

A single-crystal X-ray structure determination of the main isomer of C60F18O shows it to be an intramolecular fullerene ether rather than an epoxide, and thus the first example of an oxa-homo[60]fullerene.

Nucleophilic displacement in polyhalogenoaromatic compounds. Part 11. Kinetics of protiodeiodination of iodoarenes in dimethyl sulphoxide–methanol

The rates of methoxide-ion induced protiodeiodination of a number of polychloroiodobenzenes and their derivatives have been measured in dimethyl sulphoxide–methanol (9 : 1 v/v; 323.2 K). The true reagent under these conditions appears to be the dimethyl sulphoxide anion, and the rates of reaction in some cases appear to approach that expected of a diffusion controlled process. This corresponds to a major decrease in the efficacy of further activating substituents in the aromatic system, although deactivating groups such as p-OMe still show large effects. Chlorine promotes protiodeiodination in the order of efficiency o-Cl > m-Cl > p-Cl; the trifluoromethyl group activates displacement in the order o-CF3 > p-CF3 > m-CF3, although with much less difference between isomeric sites. o-Nitro-groups promote protiodeiodination whereas the p-nitro-group encourages methoxydeiodination. No evidence of methoxydeiodination was found in attack of the polychloroiodobenzenes, although the rates of methoxydechlorination of the corresponding polychlorobenzenes suggest that in some cases this might occur. Evidence rejecting the possible SRN1 mechanism and supporting nucleophilic attack by a carbanionic species upon iodine is presented.

The energies of some isomers of C60F8: the use of experimental and theoretical considerations to limit candidate structures

A survey of possible structures for the C60F8 molecule has been carried out, using both experimental (19F NMR data) and theoretical (structure-energy correlation) considerations to limit the number of isomers to be regarded as candidates for the previously isolated species. Several isomers are suggested as likely, with one low-energy structure in particular appearing to fulfill all the criteria better than the literature suggestion. Both this predicted isomer and that previously suggested have in common a sub-structure of a single fluorinated carbon atom surrounded by three vicinal fluorine neighbours together with a further pair of fluorine atoms added so as to generate a T-shaped motif.

Preparation of N-aryl-S,S-diphenylsulfilimines by nucleophilic attack of N-lithio-S,S-diphenylsulfilimine on aromatic compounds

Abstract N-Aryl-S,S-diphenylsulfilimines with unusual substitution patterns have been prepared by reacting the novel nitrogen nucleophile N-lithio-S,S-diphenylsulfilimine with a range of activated aromatic substrates. N-Lithio-S,S-diphenylsulfilimine is not only able to displace chloro groups in conventional aromatic nucleophilic substitution reactions, but also, unlike S,S-diphenylsulfilimine itself, can attack at hydrogen-bearing positions in ‘vicarious’ aromatic nucleophilic substitutions of hydrogen.

Structural parallels in hydrogenated and fluorinated [60]- and[70]-fullerenes

Semi-empirical molecular orbital calculations (MNDO) have been carried out on isomers of C60X36 and C70X36 (X = H, F) in order to investigate the underlying cause of the parallel behaviour of the two addends towards [60]- and [70]-fullerenes. In both series the driving force for reaction (in addition to C–X bond formation) appears, on the MNDO model, to be relief of steric strain in the fullerene cage, rather than the electronic effects on the carbon framework of the addition of hydrogen and fluorine atoms. The formation of hydrogenated and fluorinated compounds with 36 added atoms from both [60]- and [70]-fullerene appears to be coincidental, arising essentially from the fact that in both cases this number of added atoms is sufficient to maximise the relief of strain in the appropriate cage. While a T point-group structure appears significantly more stable than others for C60F36, the differences amongst isomers of C60H36 are small. The MNDO predicted structures of C70, C70X40 (X = H, F) are analysed to determine the major contributions to strain energy.

Faujasite catalysis of aromatic nitrations with dinitrogen pentoxide. The effect of aluminium content on catalytic activity and regioselectivity. The nitration of pyrazole

The reaction of 1-chloro-2-nitrobenzene with dinitrogen pentoxide in dichloromethane catalysed by H-faujasite zeolites F-712, F-720, F-780 and F-901, giving 1-chloro-2,4-dinitro- and 1-chloro-2,6-dinitrobenzene in approximately 30∶1 ratio, is a kinetically first-order process. First-order rate constants are independent of the concentration of N2O5 and proportional to the mass of catalyst used. Specific rate constants, obtained by dividing the first-order rate constant by the mass of faujasite, are constant for a given faujasite. Amongst the faujasites, they increase in approximate proportion to the aluminium content. A mechanism is proposed in which the protons in the faujasite, near aluminium in the faujasite framework, are replaced by nitronium ions derived from N2O5 in a fast pre-equilibrium process. This produces active sites for transfer of nitronium ion from faujasite to aromatic in the rate-determining step. The similar reactions of 2-nitrotoluene, too fast for kinetic study, reveal that the ratio of 2,4- to 2,6-dinitrotoluene in the product increases with the aluminium content of the faujasite.Nitration of nitrobenzene is also catalysed by faujasite. Relative reactivities of nitrobenzene, 1-chloro-2-nitro- and 1-chloro-4-nitrobenzene are compared to those found in mixed-acid nitration.Pyrazole can be nitrated readily with N2O5 over faujasites, yielding 1,4-dinitropyrazole in 80% yield under mild conditions. p