Determination of Long-Range Dipolar Couplings Using Mono-Deuterated Liquid Crystals

Abstract

A new approach is presented for the determination of long-range dipolar couplings in liquid crystals. The strategy is the use of monodeuterated compounds to observe 2H−13C splittings in the 13C NMR spectra. As examples, the H−C dipolar coupling constants have been obtained from the spectra of 4‘-cyanobiphenyl 2-deutero- and 6-deuterohexanoate over the whole nematic range. In addition, the 2H NMR spectra of these compounds taken with 1H−H dipolar decoupling show quadrupolar splitting and 1H−H dipolar coupling. Besides the information obtained from the 1D spectra, one-bond and two-bond 1H−13C dipolar coupling constants of 4‘-cyanobiphenyl hexanoate were determined using the method of proton encoded local field (PELF) spectroscopy in combination with off-magic-angle spinning (OMAS). The order parameters were calculated from the 2D spectra, and some of the coupling constants are compared with the H−C coupling constants obtained from the 1D experiments.

Fixed lock-time relaxation dispersion in the rotating frame

“…In combination with off-magic angle spinning (OMAS), this value showed a reduction to 3473 Hz [16]. Proton encoded local field spectroscopy (PELF) in combination with OMAS were also used in a similar compound (4-cyanobiphenyl hexanoate) obtaining carbon-proton couplings between 52 Hz (for long range interactions) and 5285 Hz (local interactions) [17]. By using proton and deuteron NMR spectroscopy of partially deuterated 5CB (5CB-d 15 ), proton-proton dipolar couplings up to 3919 Hz were found within the molecular core.…”

Filtering of Spinning Sidebands in 1D MAS NMR Spectra

“…On the other hand, it is very convenient to use the filtering function (3) for SSB separation in 2 H spectra with MAS. As an example, the spectra of a mixture of malonic acid-d 4 and 4 -cyanobiphenyl 6-deuterohexanoate [18] are shown in Fig. 4.…”

Determination of long range dipolar couplings in ferroelectric liquid crystals

“…An test for the molecular dynamics calculations is a comimportant class of FLCs is formed by the esters of parison between calculated and experimental long range optically active a-halocarboxylic acids with 4-alkoxydipolar coupling constants, which can be determined 4¾ -hydroxybiphenyl s [2][3][4]. These compounds exhibit by using several diOE erent NMR techniques [14][15][16][17][18][19]. We a chiral smectic C phase with very large spontaneous have found that the use of monodeuterate d LCs [14,19] polarization P S (up to 300 nC cmÕ 2 ).…”

“…These compounds exhibit by using several diOE erent NMR techniques [14][15][16][17][18][19]. We a chiral smectic C phase with very large spontaneous have found that the use of monodeuterate d LCs [14,19] polarization P S (up to 300 nC cmÕ 2 ).…”

“…to observe 2H-13C splittings in the 13C spectra gives very A variety of techniques has been used to study rich information [19]; the application of this approach molecular motion in liquid crystalline phases. Among to determine some long range dipolar coupling constants them, NMR spectroscopy has been used very successfully in three racemic ferroelectric liquid crystals is reported to give detailed information on molecular geometry, in this work.…”