Anti-proton

For the stable conformers 13a-c of a substituted ethane the vicinal HH coupling constants 3Hz for syn-protons and 15 Hz for anti-protons can be derived from Fig. 2.18. If there is rotation around the C-C single bond, the coupling protons pass through the syn configuration twice and the anti configuration once. 

For gauche protons the value of J varies from 2 1 cps and for anti protons J varies from 5-12 cps... 

Anti-protonic atoms. Recently neutron density distributions in a series of nuclei were deduced from anti-protonic atoms [30], The basic method determines the ratio of neutron and proton distributions at large differences by means of a measurement of the annihilation products which indicates whether the antiproton was captured on a neutron or a proton. In the analysis two assumptions are made. First a best fit value for the ratio I / of the imaginary parts of the free space pp and pn scattering lengths equal to unity is adopted. Secondly in order to reduce the density ratio at the annihilation side to a a ratio of rms radii a two-parameter Fermi distribution is assumed. The model dependence introduced by these assumptions is difficult to judge. Since a large number of nuclei have been measured one may argue that the value of Rj is fixed empirically. 

Fig. 4. syn- and anti-protonation, respectively, of 0-1 as a means of classification of glycosidases. 

Family 10 xylanase Cex from Cellulomonas fimi and family 11 xylanase Bex from Bacillus circulans198,199 (the first being an anti-, the second a syn-protonator) were exposed to deoxynojirimycin-related (80, Scheme 22) and isofagomine analogous (81) xylosidase inhibitors, along with the anti-protonation-selective xylobiosyl... 

W. Nerinckx, T. Desmet, K. Piens, and M. Claeyssens, An elaboration on the syn-anti proton donor concept of glycoside hydrolases. Electrostatic stabilisation of the transition state as a general strategy,... 

Similar 6 values for syn-and meso—protons but marked differences for those of anti protons... 

This suggests that the syn proton in norbornyl chloride is more acidic than the anti proton. 

The proton NMR shifts of diad, triad, and tetrad protons in an isolated chain of PP are calculated, taking into account its configurations and conformations using Pople s approximation. The agreement between the observed and calculated results, however, is insufficient with respect to the large difference between syn and anti protons and the order of tetrad protons. Here, a priori probabilities of specified conformations necessary to the estimation of the chemical shifts are calculated using Flory s matrix method. 

Another type of symmetry of importance in elementary particle physics is that entitled charge conjugation. This principle slates that if each particle in a given isolated system is replaced by its corresponding anliparticle, then no difference can be observed. For example, if. in a hydrogen atom, the proton is replaced by an anti-proton and the electron is replaced hy a positron, then this antimatter atom will behave exactly like an ordinary atom, so long as it does not come inlo contact with ordinary atoms. 

The enzyme-catalysed cyclization of (A)-[9-2 H i. H i ]gcranyl diphosphate to (45)-limonene has been found to terminate predominately by re-facial, anti proton elimination at tire cis methyl group of the intermediate (35)-l inalyl diphosphate.80... 

SCHEME 71. Syn vs. anti protonation of the lithium enolate of 2,4-dimethyltetralone by carbonyl-based adds under kinetic conditions352... 

---