Ring current, calculation

Fig.1 8. Structure of the heme group in hemoglobin and the positions of the yj-and y2-CH3 groups of the Ell valyl residue and the C-2-H of the E7 histidyl residue in the CO and oxy forms of the a chain of Hb A. The positions for the CO form (full circles) were calculated from the X-ray coordinates for the a chain of HbCO A (Baldwin, 1980), whereas the approximate positions for the oxy form (broken circles) were calculated from our NMR data and theoretical ring-current calculations. [From Dalvit and Ho (1985)].

Mallion, R.B. (1975) Some graph-theoretical aspects of simple ring current calculations on conjugated systems. Proc. Roy. Soc. London A, 341, 429-449. 

Thus in TFA the meso protons of porphine resonate at r —1.22, the (3-protons at t 0.08, and the imino protons upheld at t 14.40 168h That the meso protons are more deshielded than the other peripheral protons is reflected in the ring-current calculations 169). 

SOME COMMENTS MO COMPARISONS CONCERNING THE USE OF "RING-CURRENT" CALCULATIONS IN ELUCIDATING MOLECULAR CONFORMATIONS... 

This fascinating continuum-discrete duality in ring current calculations is a fundamental novelty in theoretical chemistry that deserves greater attention and better understanding, which adds to the great significance of this work. After the manuscript was submitted to the Journal of Computational Chemistry, unexpectedly in a letter one of the editors sent the following short report from one of the two anonymous reviewers ... 

Figure 2. Open chains (spanning trees ) that could be used for an application of McWeeny s method via eq 16 (section V) in order to perform a ring-current calculation on the conjugated hydrocarbon pyrene (14) (a) the carbon-carbon cr-bond connectivity of pyrene (b) a continuous open chain (from this semi Hamiltonian molecular-graph ) for pyrene (c) circuit completing bonds associated with the open chain in part b. (Adapted and reprinted with permission from ref 3. Copyright 1997 Research Studies Press Ltd.)...

Calculated via the equivalent of eq 16 (section V) and expressed correct to two decimal places. All relative ring currents quoted here are based on a simple, noniterative with the exception of those for pyracylene (17) and biphenylene (22) in which certain rings appear to be paramagnetic. Ring-current calculations for these species are, therefore, based on an iteratively self-consistent A... 

Application of Ring Current Calculations to the Proton NMR of Proteins and Transfer RNA... 

Thus we have omitted data based on ring current calculations. 

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