Nucleophilic cleavage products from beta-deprotonated sesquidiazabicyclooctane dication

Nucleophilic cleavage of aminoaziridinium cation 2(+) by PhS(-), N=C-, CH3CO2-, and F- results in C-N+ bond cleavage with inversion at carbon, producing essentially only the axially-substituted (X) (22/31) derivatives for the latter two cases, but 40 and 15% exo-substituted 1(X) (22/22) are initially produced for thiophenoxide and cyanide, respectively. The increase in oxidation potential for 3(CN) vs 3 (0.22 V) is the same as that for replacement of the corresponding ii by CN in an acyclic system. X-ray structures show that larger changes in nitrogen pyramidality (Delta alpha(av) + 8.4 vs + 5.8 degrees) and NN distance (-0.172 vs -0.160 Angstrom) occur upon electron loss from 3 than from 1. Despite more constricted bond angles at nitrogen, crystalline 3(+)TsO(-) is more planar than 1(+)TsO(-) (alpha(av) = 119.1 degrees vs 118.6 degrees), and the two double nitrogen inversion forms of 3(+) are estimated to differ in energy by under 0.02 kcal/mol in solution from ENDOR and ESR studies. 3(0/+) shows slower self-electron transfer than 1(0/+) (k(ex) (25 degrees C, CH3CN) similar to 300 vs 700 M(-1) s(-1)). Neither more planar nitrogens for 3(+) than for 1(+) nor slower electron transfer for 3(0/+) are predicted by AM1 calculations

Oxidized Phenyl−Substituted Sesquibicyclic Hydrazines

The effect of a− and P−phenyl substituents on the neutral, +1, and +2 oxidation states of bis−N,N&#39;− bicyclic hydrazines 1 and 2 is discussed. An a−phenyl substituent on 2 makes first electron removal 1.8 kcal/mol more difficult, but second electron removal 3.2 kcal/mol less difficult. There is no evidence for significant spin or charge delocalization into the phenyl groups of the +1 oxidation states of these compounds. Exo and endo 8−phenyl−substituted hydrazines xPh−1 and nPh−1 have electron transfer rate constants between their neutral and radical cation forms which are 85% and 55% as large as that for unsubstituted 1, which is argued to demonstrate that attaining relative orientations which allow overlap of the dinitrogen n systems at the transition state cannot be important; electron transfer proceeds through the alkyl groups. The dications ˜ P h − 2 ˜ ˜ and nPh− 22+ decompose in acetonitrile much faster than 22+ (room temperature lifetimes < 1 s for the phenylated compounds and > lo4 min for the parent

Teaching of direct posterior resin composite restorations in UK dental therapy training programmes

Aim: With the number of dental therapists involved in the delivery of dental care in the UK on the increase, and the trend towards the use of direct resin composites (composites) for the restoration of posterior teeth, this study was undertaken to describe the teaching of posterior composites in dental therapy training programmes in the UK. A secondary aim was to identify differences in techniques for posterior composites taught within these dental therapy training programmes. Methods: In 2008/9, a questionnaire seeking information on the teaching of posterior composites was distributed by email to 13 centres with dental therapy training programmes in the UK. This questionnaire sought information relating to the teaching of direct posterior composites to dental therapy students, including the amounts of preclinical and clinical teaching in respect of deciduous and permanent teeth, numbers of restorations placed, contraindications to placement, and details in respect of operative techniques. Results: Ten completed responses were received (response rate = 77%). In ten programmes, student dental therapists received clinical training in the placement of composite restorations in the occlusal surfaces of premolar and permanent molar teeth, and nine programmes included such training for two and three surface occlusoproximal restorations. The mean proportions of posterior restorations placed clinically by student dental therapists in permanent teeth using dental amalgam and composite were 52% and 46% respectively (range: amalgam = 20-95%; composite = 5-70%). Conclusion: With the exception of one programme, the teaching of posterior composites is a well established element of dental therapy training. Some variations were noted in the teaching of clinical techniques between respondent training centres. It is suggested that to ensure harmony in approaches to treatments provided by graduated therapists that training centres look to relevant consensus documents, such as those of the British Association of Teachers of Conservative Dentistry. The findings of our study are important for the future provision of oral healthcare, given the growing evidence base in favour of minimally invasive dentistry