Molecules which differ only in isotope composition
Not to be confused with isotopomers.
In chemistry, isotopologues are molecules that differ only in their isotopic composition.[1] They have the same chemical formula and bonding arrangement of atoms, but at least one atom has a different number of neutrons than the parent.
An example is water, whose hydrogen-related isotopologues are: "light water" (HOH or H2O), "semi-heavy water" with the deuterium isotope in equal proportion to protium (HDO or 1H2HO), "heavy water" with two deuterium isotopes of hydrogen per molecule (D2O or 2H2O), and "super-heavy water" or tritiated water (T2O or 3H2O, as well as HTO [1H3HO] and DTO [2H3HO], where some or all of the hydrogen atoms are replaced with the radioactive tritium isotope). Oxygen-related isotopologues of water include the commonly available form of heavy-oxygen water (H218O) and the more difficult to separate version with the 17O isotope. Both elements may be replaced by isotopes, for example in the doubly labeled water isotopologue D218O. All taken together, there are 9 different stable water isotopologues,[2] and 9 radioactive isotopologues involving tritium,[3] for a total of 18. However only certain ratios are possible in mixture, due to prevalent hydrogen swapping.
The atom(s) of the different isotope may be anywhere in a molecule, so the difference is in the net chemical formula. If a compound has several atoms of the same element, any one of them could be the altered one, and it would still be the same isotopologue. When considering the different locations of the same isotopically modified element, the term isotopomer, first proposed by Seeman and Paine in 1992, is used.[4][5]
Isotopomerism is analogous to constitutional isomerism of different elements in a structure. Depending on the formula and the symmetry of the structure, there might be several isotopomers of one isotopologue. For example, ethanol has the molecular formula C2H6O. Mono-deuterated ethanol, C2H5DO, is an isotopologue of it. The structural formulas CH3−CH2−O−D and CH2D−CH2−O−H are two isotopomers of that isotopologue.
^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (1994) "Isotopologue". doi:10.1351/goldbook.I03351
^The nine stable isotopologues are H216O, H16OD, D216O, H217O, H17OD, D217O, H218O, H18OD, D218O
^The nine tritiated isotopologues are H16OT, D16OT, T216O, H17OT, D17OT, T217O, H18OT, D18OT, T218O
^Seeman, Jeffrey I.; Secor, Henry V.; Disselkamp, R.; Bernstein, E. R. (1992). "Conformational analysis through selective isotopic substitution: supersonic jet spectroscopic determination of the minimum energy conformation of o-xylene". Journal of the Chemical Society, Chemical Communications (9): 713. doi:10.1039/C39920000713.
^Seeman, Jeffrey I.; Paine, III, John B. (December 7, 1992). "Letter to the Editor: 'Isotopomers, Isotopologs'". Chemical & Engineering News. 70 (2). American Chemical Society. doi:10.1021/cen-v070n049.p002. Retrieved 28 August 2020.
In chemistry, isotopologues are molecules that differ only in their isotopic composition. They have the same chemical formula and bonding arrangement...
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the ground state is 2.00 Bohr radius. The dihydrogen cation has six isotopologues. Each of the two nuclei can be one of the following: proton (p, the...
Deuterated acetone ((CD3)2CO), also known as acetone-d6, is a form (isotopologue) of acetone (CH3)2CO in which the hydrogen atom (H) is replaced with deuterium...
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used as the source of deuterium for preparing specifically labelled isotopologues of organic compounds. For example, C-H bonds adjacent to ketonic carbonyl...
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dimethylformamide ((CD3)2NCOD), also known as deuterated DMF, is an isotopologue of DMF ((CH3)2NCOH) in which the hydrogen atom ("H") is replaced with...
each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical...
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the light (kL) and the heavy (kH) isotopically substituted reactants (isotopologues): KIE = k L k H {\displaystyle {\text{KIE}}={\frac {k_{L}}{k_{H}}}}...
generated by ionizing the appropriate isotopologue of H2 in the presence of helium-4. The following isotopologues of the helium hydride ion, of the dihydrogen...
of the isotopes. It is an umbrella term for the more specific terms isotopologue and isotopomer, coined by Jan Kaiser and Thomas Röckmann in 2008. Toyoda...
is a white solid very similar to sodium hydroxide, of which it is an isotopologue. It is used as a strong base and deuterium source in the production of...
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substituted isotopologues; 13CH3D and 12CH2D2 are doubly substituted isotopologues. The multiple-substituted isotopologues are clumped isotopologues. The absolute...
than two atoms it is necessary to measure the spectra of two or more isotopologues, such as 16O12C32S and 16O12C34S. This allows a set of simultaneous...
one or more hydrogen atoms are substituted by deuterium atoms. These isotopologues of common solvents are often used in nuclear magnetic resonance spectroscopy...
demonstrated that the reaction of regular 2-butene with its all-deuterated isotopologue yielded C4H4D4 with deuterium evenly distributed. In this way they were...
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