Possible Observation of Parity Nonconservation by High-Resolution NMR

Abstract

In achiral conditions, a difference in the NMR spectra of the d, I forms of a chiral molecule should be a manifestation of the never observed parity nonconservation in molecules. The involved NMR parameters depend on the never measured nuclear-spin-dependent PNC potential. Calculations performed with a relativistically parameterized extended Huckel method show a difference of a few mHz in the metal resonance frequency of enantiomers, containing Pt or Pb. A discussion of the various possible limiting factors shows that such a difference could be observed.

Mirror Symmetry Breaking in Helical Polysilanes: Preference between Left and Right of Chemical and Physical Origin

“…By comparing 29 Si-NMR spectra, the degree of main chain mobility is detectable as the difference in linewidth; the sum of the shielding and deshielding terms by inner-shell electrons of the main chain could be measurable as changes in chemical shifts [21]. …”

“…However, modern theoretical studies [11][12][13][14][15][16][17][18][19][20][21][22][23]26,28,30,31,33,[36][37][38][39][40][41]43,44,46] have claimed that an image and its mirror molecule are no longer enantiomers due to an energy inequality induced by the existence of PV-WNC. Due to a parity-violating energy shift (PVES) of the electronic binding energy with a positive value, +E PV , for the image molecule and a PVES with a negative value, -E PV , for the mirror image molecule, or vice versa, PVES makes the pair become a diastereomer, exhibiting subtle differences in physical properties and chemical processes.…”

“…The parity-violating energy difference (PVED) between image and mirror image molecules is given as PVED = E PV -(-E PV ) = 2•E PV . Numbers of theoretical studies have discussed that the occurrence of PVES may appear spectroscopically as slight differences in electronic transition energies [13,16,20], vibrational frequencies [43], ro-vibrational frequencies [17,41], NMR chemical shifts [21], circular polarization in electronic transition and vibrational frequency regions [18,43], a concept hereafter called the molecular parity violation (MPV) hypothesis in this article.…”

Measuring molecular parity nonconservation using nuclear-magnetic-resonance spectroscopy

“…However, based on the calculations presented in Refs. [15,16], the value for high-Z nuclei like 129 Xe [34][35][36], 195 Pt, 203 Tl, 205 Tl, and 207 Pb, is estimated to be 4-5 orders of magnitude larger. Therefore, an experiment using one of these nuclei and achieving the same measurement precision as demonstrated here may be able to observe molecular parity violation.…”

NMR and parity nonconservation. Experimental requirements to observe a difference between enantiomer signals

“…Due to the weak interactions, a nucleus is chiral in itself, and thus the corresponding nuclei of a molecule, which exists in two enantiomeric forms, R and S, respectively, are in a diastereomeric environment and may exhibit NMR resonance frequency differences. 15 For several reasons, including (1) the great variety of nuclei which can be considered, (2) the use of ultrahigh-resolution and very high field NMR spectrometers, (3) the contribution of the spin-dependent PNC terms, which usually play a minor role in the PNC experiments, the search for a difference in the two enantiomers spectra appears to be an interesting and possible successful challenge for observing PNC in molecules.…”