endo-Anomeric and exo-anomeric effects in 2-substituted tetrahydropyrans

Booth, Harold Simmons; Khedhair, Khedhair A.

doi:10.1039/c39850000467

Cited by 49 publications

(23 citation statements)

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“…The calculated GFED ax-eq for compounds 1-3 are 2.78, 2.60 and 1.99 kcal mol À1 , respectively, as calculated by B3LYP/6-311+G**//B3LYP/6-311+G** level of theory. The calculated GFED ax-eq and also other thermodynamic parameters for the axial and equatorial conformations of compound 1 are in good agreement with reported experimental data (see Table 2) [14,15].…”

Section: Resultssupporting

confidence: 87%

“…Although, there is insufficient experimentally published information about the anomeric interactions in compound 1 [13][14][15][16][17] but there is no experimental or quantitative theoretical published data about the donor-acceptor delocalization effects on the conformational properties of 2-9. In this work, the stereoelectronic interactions associated with the AE and also conformational and structural properties of compounds 1-9 were investigated computationally using both ab initio MO and DFT methods [18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

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Stereoelectronic interaction effects (associated with the anomeric effects) on the conformational properties of 2-methylaminotetrahydropyran, 2-methylaminotetrahydrothiopyran, 2-methylaminotetrahydroselenopyran and their analogous containing P and As atoms: An Ab initio study and NBO analysis

Nori‐Shargh

Yahyaei

2009

Journal of Molecular Structure: THEOCHEM

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Stereoelectronic interaction effects (associated with the anomeric effects) on the conformational properties of 2-methylaminotetrahydropyran, 2-methylaminotetrahydrothiopyran, 2-methylaminotetrahydroselenopyran and their analogous containing P and As atoms: An Ab initio study and NBO analysis

Nori‐Shargh

Yahyaei

2009

Journal of Molecular Structure: THEOCHEM

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“…A value of 1.35 kcal/mol has been estimated for the anomeric effect in 2-MeS-tetrahydropyran, from the reported AGO value (0.35 in CC14 (39)), and the A value of MeS (1.0 kcal/mol (40)). A corresponding value of 1.29 kcal/mol in CFC13/CDC13 solvent can be estimated for 2-Me0-tetrahydropyran from the thermodynamic data for this compound and methoxycyclohexane (41). However, taking into account the conformational free energies for the axial-equatorial equilibria in 2-Me-tetrahydropyran (2.86 kcal/mol (42)) and methylcyclohexane (1.74 kcal/mol (43)) leads to experimental free energy anomeric effects of 1.67 and 1.99 kcal/mol, respectively, in 2-Me0-and 2-MeS-tetrahydroPYrm…”

Section: Dimethyl Ether and Dimethyl Suljidementioning

confidence: 99%

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

Wolfe¹,

Pinto²,

Varma³

et al. 1990

Can. J. Chem.

152

105

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The magnitude of a one-bond C-H coupling constant depends upon the chemical environment of the hydrogen atom and, especially, upon its stereochemical relationship to vicinal lone electron pairs. However, a lone electron pair is not essential for the observation of a stereoelectronic effect, since even cyclohexane exhibits different axial and equatorial C-H coupling constants. We propose the name "Perlin Effect" to describe such observations. An analysis of the extensive experimental data regarding the Perlin Effect reveals that, in cyclohexane and in six-membered rings having one or more heteroatoms of the first row attached to the carbon of interest, ' J~-~ is always larger for an equatorial hydrogen than for an axial hydrogen. The magnitude of the Perlin Effect is reduced when the carbon carrying the hydrogen of interest is attached to first row and second row atoms or heteroatoms, and it reverses when the carbon atom carries two heteroatoms from below the first row.The existence of the Perlin Effect in nuclear magnetic resonance spectra is reminiscent of an infrared effect known as the Bohlmann bands, whose origin has previously been explained by quantitative perturbational molecular orbital (PMO) theory in terms of the effects of lone electron pairs upon the lengths and strengths and, therefore, the chemical reactivities of vicinal C-H bonds. Since the magnitude of a one-bond C-H coupling constant is expected to vary inversely with bond length, the origins of the Perlin Effect and of the Bohlmann bands would seem to be the same, i.e., the longer (weaker) C-H bond has the smaller one-bond coupling constant. This expectation has now been confirmed: for 25 molecules, representing a total of 35 different kinds of C-H bonds, the bond lengths, stretching force constants, and charge distributions have been determined from fully optimized 6-3 1 G* molecular orbital calculations. In nine of ten cases for which experimental data exist for pairs of diastereomeric or diastereotopic hydrogens, the shorter C-H bond of the pair has the larger coupling constant; in the tenth case, the experimental difference is only 1-2 Hz. Moreover, a global analysis of the data in terms of the equationwhere J is an experimental coupling constant, q is a total atomic charge, and r is a C-H bond length, correlates 23 different types of C-H bonds linearly with a correlation coefficient of 0.9 15. The C parameter is the leading term of the correlation. Among the systems studied theoretically are eight molecules of the type CH3CHXY (Y = OH, SH; X = F, C1, OH, SH), which are representative of systems containing both endocyclic and exocyclic first row and second row anomeric effects. The exocyclic effect is found to be very similar for first row and second row substituents, but the endocyclic effect is larger for the first row substituent. Both findings agree with experimental data in solution. Finally, quantitative PMO analysis has been employed to analyse the origins of the different C-H bond lengths in the various molecules of the study. dans...

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“…We disagree. It is to be kept in mind, however, now that the origin of the anomeric effect has become established (8,9), that an anomeric effect (AA) must be considered as the difference between the sum (A3,) of the endoand exo-anomeric effects in the equatorial conformer and the sum (A3a) of these for the other conformer (22,23). It is on this basis that the anomeric effect for 3 is defined as shown in expression [3].…”

Section: Imentioning

confidence: 99%

Influence of solvent on the magnitude of the anomeric effect

Praly¹,

Lemieux²

1987

Can. J. Chem.

223

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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endo-Anomeric and exo-anomeric effects in 2-substituted tetrahydropyrans

Cited by 49 publications

References 1 publication

Stereoelectronic interaction effects (associated with the anomeric effects) on the conformational properties of 2-methylaminotetrahydropyran, 2-methylaminotetrahydrothiopyran, 2-methylaminotetrahydroselenopyran and their analogous containing P and As atoms: An Ab initio study and NBO analysis

Stereoelectronic interaction effects (associated with the anomeric effects) on the conformational properties of 2-methylaminotetrahydropyran, 2-methylaminotetrahydrothiopyran, 2-methylaminotetrahydroselenopyran and their analogous containing P and As atoms: An Ab initio study and NBO analysis

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

Influence of solvent on the magnitude of the anomeric effect

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