Equivalent isotopic isomers

Fig. 5.6 Vapor pressure differences between equivalent isotopic isomers of dideuteroethylene. The three mercury levels shown (left to right) measure the vapor pressures of ordinary ethylene C2D4, /ram-ethylene-1,2dj, and ei.v-cthylene- l dj. The vapor pressure of gem-ethylene-1,ld2 is very similar to the cis-isotopomer and is not shown in this photograph (Bigeleisen, J., Science 147, 463 (1965))...

NOTE The correct term for an individual isotope of an element, for example C, is nucUde , but the word isotope is in loose common usage. The use of isotope , without further qualification, is equivalent to saying that 1-butene is an isomer , without saying of what.]... 

Chemical isomer shifts for the tungsten isotopes are generally within experimental error of the observed line position. The only unambiguous example is for where a shift of —0-25(5) mm s was found between a tungsten absorber and a WClg absorber [51]. An approximate estimate of dR/R = 0-65 X 10 was derived. Equivalent shift values for and were 0-17(46) and —0-10(22) mm s, well within experimental error. 

The mathematical term topology involves geometrical properties which remain invariant given continuous deformation in space [2, 3]. Two structures are said to be topological equivalent or isotopic if they can be interconverted into one another by continuous deformation. If not they are called topologically distinct or not isotopic. One of these topological invariants is connectivity. Structures with identical connectivity are termed homeomorphic. Transferring these terms to molecular structure results in three types of isomers ... 

Equivalent Isomers have the same Isotope chemistry. 

An enantioselective Stetter employing a chiral NHC and Hunig s base (EtNPr-j ) in methanol at 0°C has its yield massively boosted by addition of 1 equiv of catechol (1,2-dihydroxybenzene), whereas other phenols such as isomers of catechol or its monomethyl ether have negligible effect. Studies of deuterium kinetic isotope effects suggest that initial proton transfer from catechol (97) to form the aryl anion equivalent (98) is turnover limiting. Intramolecular examples are also described, requiring subpercentage amounts of NHC, base, and catechol. 

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