Anomeric Interactions Research Articles

Lack of manifestation of an anomeric effect in 2‐diphenylphosphinoyl‐1, 3‐dioxane and 2‐diphenylphosphinoyl‐1, 3‐oxathiane1

AbstractThe spectroscopic evidence for the predominance of the equatorial conformers in the title compounds was confirmed by the study of derivatives containing counterpoise substituents, and by chemical equilibration of anancomeric models. ΔG°C [P(O)Ph2] ≳ 3·2 kcal/mol was determined in the dioxane, and ΔG°C [P(O)Ph2] = 1·42 ± 0·12 kcal/mol in the oxathiane. It follows then that the strong anomeric interaction observed previously in SCP segments does not show up in the six‐membered heterocycles 2 and 7, which contain OCP moieties. This may be due to an inherent inability of oxygen to act as an electron donor to the axial P(O)Ph2 substituent, or to a dominant repulsive steric interaction in the axial conformers.

The anomeric effect at silicon

The anomeric effect at silicon has been studied by ab initio calculations. The geometries and energies of H 2Si(XH) 2, X = O, S were optimized with the basis sets 3-21G, 3-21G (*), and 6-31G *. Single point MP3/6-31G * //6-31G * calculations were also carried out. H 2Si(XCH 3) 2, X = O, S, were studied with the 3-21G basis set. All compounds are most stable in the gauche, gauche conformation, pointing to the operation of an anomeric effect. The total anomeric interactions given by the energies of the equations: H 2Si(XH) 2 + SiH 4 → 2H 3SiXH are (MP3/6-31G *): 8.6 and 2.2 kcal/mol for X = O and X = S, respectively. Rotation barriers on going from the ( g, g), to the ( g, a) and to the ( a, a) conformations are (MP3/6-31G *, kcal/mol): 2.5 and 3.8 in H 2Si(OH) 2 and 2.1 and 3.2 in H 2Si(SH) 2. Thus, the anomeric effect in H 2Si(OH) 2 is large, although smaller than in H 2C(OH) 2. In H 2Si(SH) 2 and H 2C(SH) 2 the anomeric effects are comparable, and both relatively small. The anomeric effect is predicted to be important in determining the conformations of compounds with silicon bonded to 2 oxygens such as R 2Si(OR′) 2, disilaoxiranes, and related molecules.

Conformational preference of the s=O group.3. Continued evidence for a very strong s-s=o anomeric interaction from the nmr spectroscopic study of 44,5,5-tetramethyl-1,2-dithiane 1-oxide

The 1H and 13C NMR behavior of the title compound ( 4 ) was studied in order to determine the conformational preference of the S=O group in this heterocycle. The NMR spectra were assigned by a combination of homo- and heteronuclear double irradiation, as well as nuclear Overhauser enhancement experiments. From the results of variable temperature, solvent effects and shift reagent experiments, it is concluded that the axial conformer dominates the equilibrium to such an extent that no contribution of the equatorial isomer is recorded. This result suggest that ΔG° ( 4 -ax 4 -eq)⩾ 1.7 kcal mol , and because the axial conformer suffers from a syn -diaxial Me/S=O interaction, a ΔG° ⩾ 3.0 kcal mol for the conformational equilibrium in the parent 1,2-dithiane mono-S-oxide ( 1 ) can be extrapolated. Some discussion of the possible mechanism responsible for such strong anomeric effect is presented.

Sulfur-carbon-phosphorus anomeric interactions. 5. Conformational preference of the diphenylthiophosphinoyl group [(C6H5)2P(S)] in cyclohexane and in the 1,3-dithian-2-yl ring

Sulfur-carbon-phosphorus anomeric interactions. 5. Conformational preference of the diphenylthiophosphinoyl group [(C6H5)2P(S)] in cyclohexane and in the 1,3-dithian-2-yl ring

Conformation of 2-phosphoryl and 2-thiophosphoryl 1,3-dithianes and related compounds. Comments on the origin of S-C-P anomeric interactions.

A relationship was found between the γ-effect values in 13C NMR spectra and the solution conformation of the title compounds. Base-catalyzed equilibration of anancomeric 2-phosphoryl and 2-thiophosphoryl substituted 5-t-butyl-1,3-dithianes showed that axial preference increases in the order: Ph 2P(S)<Ph 2P(O)<(MeO) 2P(O). Explanation of this phenomenon is proposed, based also on the results of molecular mechanics calculations.

ChemInform Abstract: Conformational Analysis of S‐C‐P Anomeric Interactions. Part 3. The Conformational Preference of the Diphenylphosphinoyl Group in Cyclohexane.

ChemInform Abstract: Conformational Analysis of S‐C‐P Anomeric Interactions. Part 3. The Conformational Preference of the Diphenylphosphinoyl Group in Cyclohexane.

Conformational analysis of sulfur-carbon-phosphorus anomeric interactions. 3. The conformational preference of the diphenylphosphinoyl group in cyclohexane

Conformational analysis of sulfur-carbon-phosphorus anomeric interactions. 3. The conformational preference of the diphenylphosphinoyl group in cyclohexane

Study of the anomeric effect in 2-substituted 1,3-dithianes

The conformational analysis of several 2-substituted 1,3-dithianes made possible the evaluation of S-C-Y anomeric interactions, where Y = SCH 3, SC 6H 5, CO 2CH 3, CO 6H 5, CO 2H and N(CH 3) 2. The relative magnitude of the effects observed for these groups [ΔG° dithiane(Y) - ΔGδ cyclohexane(Y)] can be explained in terms of the combined influence of dipole/dipole and two-electron stabilizing interactions (stereoelectronic effect).

Bond Angles in Lactones and Lactams

AbstractThe carbonyl group in lactones and, to a lesser extent, in lactams tends to show a CCO angle that is larger than the OCO or NCO angle, the difference increasing in magnitude as the ring size decreases. The observed trend provides information on ratios of force constants characterising the flexibility of the s‐cis‐ester group and may be interpreted in terms of incipient chemical reaction to −O(CH2)nCO+. Molecular orbital calculations (MINDO/3, MNDO, EH) for model compounds provide an electronic interpretation of this angle difference in terms of an anomeric interaction between the p‐type lone pair on the carbonyl O‐atom and the antibonding C‐O or C‐N orbital.

ChemInform Abstract: CONFORMATIONAL ANALYSIS OF SULFUR‐CARBON‐PHOSPHORUS ANOMERIC INTERACTIONS. 2. ‐RAY CRYSTALLOGRAPHIC EVIDENCE AGAINST THE IMPORTANCE OF NS .FWDAR . ΣC‐P CONJUGATION IN AXIAL 2‐(1,3)DITHIANYLDIPHENYLPHOSPHINE OXIDE

Chemischer InformationsdienstVolume 16, Issue 2 Organoelement Compounds ChemInform Abstract: CONFORMATIONAL ANALYSIS OF SULFUR-CARBON-PHOSPHORUS ANOMERIC INTERACTIONS. 2. -RAY CRYSTALLOGRAPHIC EVIDENCE AGAINST THE IMPORTANCE OF NS .FWDAR . ΣC-P CONJUGATION IN AXIAL 2-(1,3)DITHIANYLDIPHENYLPHOSPHINE OXIDE E. JUARISTI, E. JUARISTISearch for more papers by this authorB. A. VALENZUELA, B. A. VALENZUELASearch for more papers by this authorL. VALLE, L. VALLESearch for more papers by this authorA. T. MCPHAIL, A. T. MCPHAILSearch for more papers by this author E. JUARISTI, E. JUARISTISearch for more papers by this authorB. A. VALENZUELA, B. A. VALENZUELASearch for more papers by this authorL. VALLE, L. VALLESearch for more papers by this authorA. T. MCPHAIL, A. T. MCPHAILSearch for more papers by this author First published: January 15, 1985 https://doi.org/10.1002/chin.198502283Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue2January 15, 1985 RelatedInformation

Conformational analysis of sulfur-carbon-phosphorus anomeric interactions. 2. X-ray crystallographic evidence against the importance of nS .fwdarw. .sigma.C-P conjugation in axial 2-[1,3]dithianyldiphenylphosphine oxide

Etude par diffraction RX de la structure du r-(diphenylphosphoryl)-2-c,c-dimethyl-4,6 dithionne-1,3. Cristallisation dans le systeme monoclinique, groupe C2/c et affinement de la structure jusqu'a R=0,048. Conformation chaise de l'heterocycle

Anomeric effects involving a carbon–sulphur bond: the X-ray crystal structure of methyl (Z)-2-methoxy-3-methyl-2-(N-methylanilino)-4-oxothiazolidin-5-ylidene-ethanoate

In the X-ray crystal structure of the title compound (6) the C(2)–S(1) bond is antiperiplanar to two lone pairs from the 2-methoxy-and 2-(N-methylanilino)-groups and is lengthened to 1.880(2)A. The second lone pair on the 2-methoxy oxygen atom is antiperiplanar to the endocyclic C–N bond. The crystallographic evidence for anomeric interactions between oxygen or nitrogen lone pairs and C–S bonds is discussed and the latter appear to be stronger. Crystal data for (6): C15H18N2O4S, Mr= 322.4, triclinic, P, a= 8.344(1), b= 10.045(5), c= 10.905(2)A, α= 106.52(3), β= 109.99(1), γ= 97.10(2)°, Z= 2, Dc= 1.34 g cm–3, µ(Mo-Kα)= 0.59 mm–1, final R-value = 0.039 for 1 981 reflection with I3σ(I).

Axial preference of 2-[1,3-dithianyl]diphenylphosphine oxide. A strong S-C-P anomeric interaction

Axial preference of 2-[1,3-dithianyl]diphenylphosphine oxide. A strong S-C-P anomeric interaction

ChemInform Abstract: HETERODIENE SYNTHESIS PART 12, THE CONFORMATIONAL ANALYSIS OF CIS AND TRANS 2‐ALKOXY‐4‐PHENYL‐2,3‐DIHYDROPYRAN(2,3‐C)PYRAZOLES, STERIC INTERACTIONS AND THE ANOMERIC EFFECT

Abstract The conformational equilibria of a homogeneous series of cis and trans 2-alkoxy-4-phenyl-2,3-dihydropyran[2,3-c] pyrazoles have been investigated by a graphical method, and the preferences are rationalized in terms of steric interactions between the 4 and 5-substituents and of the anomeric effect. The anomeric interaction depends upon the nature of the alkoxy group and the conformational free-energy differences correlate with the steric parameters E s .

Heterodiene syntheses—XII : The conformational analysis of cis and trans 2-alkoxy-4-phenyl-2,3-dihydropyran[2,3-c] pyrazoles: Steric interactions and the anomeric effect

The conformational equilibria of a homogeneous series of cis and trans 2-alkoxy-4-phenyl-2,3-dihydropyran[2,3-c] pyrazoles have been investigated by a graphical method, and the preferences are rationalized in terms of steric interactions between the 4 and 5-substituents and of the anomeric effect. The anomeric interaction depends upon the nature of the alkoxy group and the conformational free-energy differences correlate with the steric parameters E s.