Bond length and reactivity. Stereoelectronic effects on bonding in acetals and glucosides

Briggs, Andrew J.; Glenn, Robert; Jones, Peter G.; Kirby, Anthony J.; Ramaswamy, Padmini

doi:10.1021/ja00333a014

Cited by 127 publications

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“…Comparisons of bond lengths between the three series of compounds are thus unaffected by conformational differences. The length of the C-OAr bond in 1-methoxymethoxy-3,5-dinitrobenzene is 1.431 (3)A, lying between the lengths expected [from the linear correlations given by Briggs et al (1984)] for the corresponding bonds of an axial tetrahydropyranyl acetal (1.450 A)or ct-glucoside (1-420A) derived from a phenol of pK a 6.68 (Martin & Butler, 1939). The plot of the C-OR bond length against the pK a of ROH for the five organic compounds for which accurate crystal structures are available* (Fig.…”

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confidence: 67%

“….~ C1121 coefficient r = 0.979) of slope -3.74 x 10 -3. This slope is a measure of the sensitivity of the length of the C-OR bond to the nature of the leaving group (RO-), and it too lies between the slopes observed for the corresponding plots for axial tetrahydropyranyl acetals and ct-glucosides (6-5 x 10 -3 and 1-0x 10 -3 respectively: Briggs et al, 1984). Thus the length of the C-OR bond (to the more electronegative oxygen atom) in three series of acetals with varying substitution at carbon shows a linear correlation with reactivity as the leaving group OR is varied.…”

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confidence: 92%

“…Our work on bond length and reactivity in tetrahydropyranyl acetal (1) and glucoside systems Briggs, Glenn, Jones, Kirby & Ramaswamy, 1984) has shown that there is a very simple relationship between the length of an acetal C--OR bond and the rate at which it is broken hydrolytically: in a given series, the longer the bond, the more easily it is broken. Furthermore, there is some evidence that this generalization also holds for comparisons of acetals from different series.…”

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confidence: 99%

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Bond length and reactivity. Structure of 1-methoxymethoxy-3,5-dinitrobenzene, C8H8N2O6

Jones¹,

Sheldrick²,

Kirby³

et al. 1985

Acta Crystallogr C

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Abstract. M r = 228.17, orthorhombic, P212121, a = 5.387 (2), b= 11.053 (2), c= 16.783 (3)A, V= 999.3 (5)/k 3, Z = 4, D x = 1.516 (8) g cm -3, ,~(Mo Ka) = 0.71069 A,/2 = 1-0 cm -1, F(000) = 472, T= 293 K. R =0.041 for 1654 observed reflections. The C-O bond length to the leaving group (referred to acetal hydrolysis) is 1.431 (3)/k; this forms part of a linear correlation between bond length and reactivity in formaldehyde acetals MeOCH2-OR. The conformation about the acetal centre is close to (-sc,-sc) with torsion angles as expected for an acyclic acetal.

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confidence: 67%

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confidence: 92%

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confidence: 99%

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Bond length and reactivity. Structure of 1-methoxymethoxy-3,5-dinitrobenzene, C8H8N2O6

Jones¹,

Sheldrick²,

Kirby³

et al. 1985

Acta Crystallogr C

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“…The changes in the atomic orbital coefficients on H I , H2, and on F reflect the adjustment of the charge distribution and secondary overlap to the smaller FCO angle. Table 1 summarizes experimental data, taken from X-ray and neutron diffraction crystal structures, of a-and P-pyranoses and pyranosides ( 14-17), 1 -axially and 1 -equatorially oriented P-D-xylopyranosyl fluorides (18), and axial and equatorial tetrahydropyranyl acetals (16). In all of these structures the 0'-CI-X, valence bond angle is systematically larger than the tetrahedral value when X is axial, and systematically smaller than the tetrahedral value when X is equatorial.…”

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confidence: 99%

Bond angle variations in XCY fragments and their relationship to the anomeric effect

Pinto

Schlegel²,

Wolfe

1987

Can. J. Chem.

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The crystal structures of 2-substituted heterocyclohexanes containing exocyclic X and endocyclic Y exhibit systematic variations in their XCY bond angles. When X is in the more stable axial orientation, corresponding to the anomeric effect, the XCY angle is larger than tetrahedral; when X is in the equatorial orientation the XCY angle is smaller than tetrahedral. These geometrical effects are predicted by the perturbational molecular orbital analysis employed previously to account for the existence of the anomeric effect and its variation with changes in X and Y. Ab initio molecular orbital calculations, with full geometry opimization, of selected conformations of XCH2YH molecules also reproduce this geometrical effect. The bond strengthening observed in XYCH2 is an electrostatic (coulombic) effect in which one substituent causes a change in the charge density at the central carbon and this, in turn, causes a change in the length of the bond to the second substituent (5-7). The XCY bond angles in XYC=CH2 and the torsional behaviour and bond length variations in RXCH2YR1 have been rationalized, both qualitatively (1, 6, 8) and quantitatively (1,6,9), by a perturbational molecular orbital (PMO) treatment that focuses on the two-orbital two-electron stabilizing orbital interactions that contribute to the HOMO of XYCAB. In this treatment the relevant interaction involves a doubly occupied nonbonding orbital on X and an unoccupied acceptor orbital on YCAB or, alternatively, a doubly occupied nonbonding orbital on Y and an unoccupied acceptor orbital on XCAB (1,9). The magnitude of this interaction is proportional

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“…Certainly, the values for these stereoelectronic contributions to molecular stability will depend on the electronegativities of the substituents, both on the pyranose ring and on the aglycon (16). As will be discussed below, the solvent also appears to influence the values of exo-anomeric effects.…”

Section: Imentioning

confidence: 99%

Influence of solvent on the magnitude of the anomeric effect

Praly¹,

Lemieux²

1987

Can. J. Chem.

221

150

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This paper is dedicated to Dr. 0. E. (Ted) Edwards J.-P. PRALY and R. U. LEMIEUX. Can. J. Chem. 65, 213 (1987). A novel application of I3c nuclear magnetic resonance provided the effects of solvent polarity and hydrogen-bond formation on the conformational equilibria for a range of 2-substituted tetrahydropyrans and the results are interpreted in terms of how solvent affects the competition between the endo-and exo-anomeric effects in determining the magnitude of the anomeric effect. In accord with the generally accepted origin of the endo-and exo-anomeric effects (anti-periplanar n-a* interaction of the oxygen lone-pair orbital with the antibonding orbital of the adjacent C-0 bond), the exo-anomeric effect for the a anomer is expected to be weaker because charge delocalization from the glycosidic oxygen to anomeric center is in competition with delocalization from the ring-oxygen atom. The effects of solvent on the relative magnitudes of the endo-and exo-anomeric effects are then considered to arise from the formation of specific complexes with the solvent, and the exo-anomeric effect of a P-glycoside is more strongly influenced. It is contended that hydrogen bonding of solvent to the ring oxygen increases the exo-anomeric effects. For this reason water is particularly effective for the strengthening of the exo-anomeric effect and, thereby, the conformational rigidity of glycosides. Experimental evidence is presented that indicates that the anomeric hydroxyl groups of free sugars dissolved in water tend to prefer the equatorial orientation because these provide stronger hydrogen bonds as proton donors to water.

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Bond length and reactivity. Stereoelectronic effects on bonding in acetals and glucosides

Cited by 127 publications

References 0 publications

Bond length and reactivity. Structure of 1-methoxymethoxy-3,5-dinitrobenzene, C8H8N2O6

Bond length and reactivity. Structure of 1-methoxymethoxy-3,5-dinitrobenzene, C8H8N2O6

Bond angle variations in XCY fragments and their relationship to the anomeric effect

Influence of solvent on the magnitude of the anomeric effect

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