17 O NMR spectroscopy: Proton–oxygen coupling in simple alcohols at natural abundance

Well resolved natural abundance I7O NMR spectra of 27 mono-, di-, tri-and tetrahydroxybicyclol2.2.1 I heptenes and -heptanes (norbornenes or norbornanes), their methylated derivatives and some related compounds were measured for 0.5 M or saturated solutions in acetonitrile at 65°C. In addition, the "0 NMR chemical shifts of 14 aliphatic and alicyclic alcohols were also determined for reference purposes. The I7O NMR chemical shifts of all compounds were assigned. Both methyl-and hydroxyl-induced deshielding &effects were consistent with those reported in the literature. Similarly, observed shielding y-effects were in agreement with the earlier observations and characteristic especially for mutual y-gauche and -eclipsed orientations of substituents. In addition, clear shielding &effects (up to 10 ppm) were observed in tri-or tetrahydroxynorbornanes. These &effects can be related to the attractive van der Waals interactions observed earlier in "C NMR chemical shifts.

Section: Scheme2mentioning

confidence: 94%

Configurational effects in ¹⁷O NMR chemical shifts of hydroxyl‐substituted, bicyclo [2.2.1]heptenes and ‐heptanes, their methylated derivatives and some related compounds

Kolehmainen

Laihia

1993

¹⁷O NMR spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes

Boykin

Чандрасекаран

Baumstark

1993

Natural abundance "O NMR data for fifteen 2-and 4-substituted phenols, ten 3-and 5-substituted 2-hydroxybeozaidehydes and eight 3-substituted benzaidehydes, recorded at 75 "C in acetonitrile are reported. The cbemicai shift change due to intramolecular bydrogen bonding for tbe phenolic oxygen was found to be 10-14 ppm shielding. In acetonitrile, the "O NMR cbemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The "O NMR cbemical shifts of the Csubstituted phenols gave an excellent correlation (r = 0.990) with anisole '"0 NMR data; the data also correiated moderately weil with u-(r = 0.974).The cbemical shifts of the 3-substituted benzaidehydes were correlated with u+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2-hydroxybenzaldehydes versus the carbonyl data for Isubstituted benzaldehydes gave a slope of 0.87 and witb r = 0.960. The plot of tbe Csubstituted phenoi data witb tbat for OH of the corresponding 2-bydroxybenzaidehydes gave a siope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly IJ(0H) = 58-92 Hzj. MM2 and MOPAC calculations predict that the hydrogen bond distances and andes for the substituted 2-hydroxybenzaldehydes and the partial atomic cbarges for the carbonyl groups (AM1) were essentially constant. After corrections for electronic effects the cbemicai shift changes due to bydrogen bonding for the donor (A6,,,) aod acceptor (A6nBA) of the carbonyLpheno1 intramolecular bonding system were 5-12 and 30 f 2 ppm, respectively. The A6,,, value was between those for keto and ester acceptors consistent with the relative basicity of the aidehyde group. The A&n vaiue was substantiaily larger than those for pbenoiic donors to keto and ester groups.

Substituted methyl 5β‐cholan‐24‐oates. I—¹⁷O NMR spectral characterization

Kolehmainen

Kaartinen

Kauppinen

et al. 1994

Methyl esters of four common bile acids, 3a-hydroxy-5gcholan-24-oic (lithocholic) acid, 3a,7a-dihydroxy-5~ cholan-24-oic (chenodeoxycholic) acid, 3a,l2udihydroxy-5~holan-24-oic (deoxycholic) acid and 3a,7a,lZatrihydroxy-5&cholan-24-oic (cholic) acid, and 14 acetylated, trifluoroacetylated, mesylated and 0x0 derivatives of methyl 5gcholan-24-oates were prepared and their "0 NMR spectra recorded. In spite of their relatively high molecular masses and the rigid molecular structure of the steroid skeleton, most of the oxygens included in these structures gave well resolved '"0 NMR resonance lines at natural abundance in 0.25-0.5 M acetonitrile solutions at 75OC. In agreement with the present ''0 NMR results, molecular mechanics calculations revealed that a hydroxy substituent located at the &-position clearly differs from the hydroxyls at the 7a-and 12u-positiom. This is due to the fact that the 3u-hydroxyl possessing only two y-carbons at antiperiplanar positions is less shielded than the other hydroxyls influenced also by the shielding effects of 'y-guuche carbons. The spectral deconvolution of the overlapping signals of the 7a-and 12a-bydroxyls is based on a computer-aided method or on chemical substitutions. The 0x0 groups located at the longitudinal (foxo) vs. transversal (7-and 120x0) axes of the steroid framework show very different quadrupolar relaxation properties and '"0 NMR linewidths owing to the strong anisotropy of overall molecular motion. In contrast, the I7O NMR linewidths of all 3a-, 7a-and 12a-hydroxyls are very similar and clearly smaller than those of the corresponding 0x0 groups, revealing that their quadrupolar relaxation is merely determined by their internal rotation rather than by the overall molecular motion.