Conformational analysis in saturated heterocyclic compounds

Eliel, Ernest L.

doi:10.1021/ar50025a001

Cited by 167 publications

(54 citation statements)

References 45 publications

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“…Our approach is experimental in nature and focusses on the svstematic evaluation of substituent effects on conformational equilibria. Although there have been many experimental (1) and theoretical (2) investigations of such X-C-Y anomeric interactions (3), these studies have generally dealt with interactions involving first-and second-row elements. For instance, second-row elements, sulfur and phosphorus.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and conformational analysis of 2-arylseleno-1,3-dithianes. Crystal and molecular structure of 2-(4-methoxyphenylseleno)- and 2-(4-trifluoromethylphenylseleno)-1,3-dithiane

Pinto¹,

Sandoval‐Ramírez²,

Sharma³

et al. 1986

Can. J. Chem.

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Can. J. Chem. 64, 732 (1986). The synthesis of 2-(4-methoxyphenylse1eno)-l,3-dithiane 3 and 2-(4-trifluoromethylphenylse1eno)-l,3-dithiane 5 from 2-chloro-l,3-dithiane 1 and the corresponding sodium arylselenolates is described. Nuclear magnetic resonance spectroscopic investigation of the products indicates that the compounds exist predominantly in a conformation in which the arylseleno moiety adopts an axial orientation. X-ray crystallographic investigation indicates that the 1,3-dithiane ring exists in the chair conformation with the arylseleno moiety in the axial orientation. Compound 3 is orthorhombic, space group P212121 with a = 5.449(2) A, b = 9.217(2) A, c = 24.860(3) A, V = 1248.5 A3, Z = 4. The structure was refined to R = 0.038 for 689 reflections with I > 2.3u(I). Compound 5 is monoclinic, space group C2/c, with a = 28.628 (7) On dCcrit la synthkse du (mCthoxy-4 phCnylsC1Cno)-2 dithiane-l,3 (3) et du (trifluoromtthyl-4 phtnylsC1Cno)-2 dithiane-l,3 (5) P partir du chloro-2 dithiane-1,3 (1) et des arylsCltnolates de sodium correspondants. Une Ctude des produits par spectroscopie rmn indique que les composCs existent principalement dans une conformation dans laquelle la portion arylsClCno se trouve dans une orientation axiale. Des ttudes par diffraction des rayons-X indiquent que le cycle dithiane-1,3 existe dans une conformation chaise et que les groupements arylsClCno se trouvent dans une conformation axiale. Le composC 3 est orthorhombique, groupe d'espace P212121, avec a = 5,449(2), b = 9,217 (2) [Traduit par la revue]

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Section: Introductionmentioning

confidence: 99%

Synthesis and conformational analysis of 2-arylseleno-1,3-dithianes. Crystal and molecular structure of 2-(4-methoxyphenylseleno)- and 2-(4-trifluoromethylphenylseleno)-1,3-dithiane

Pinto¹,

Sandoval‐Ramírez²,

Sharma³

et al. 1986

Can. J. Chem.

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“…according to [2] The abnormally large value for 180" (6-8) rules out the possibility of a planar conformation for the TH-ZTH ring.…”

Section: Introductionmentioning

confidence: 99%

Part I. Conformational analysis of thiazolidine-2-thione

Chanon¹,

Rajzmann²,

Chanon³

et al. 1980

Can. J. Chem.

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. Can. J . Chem. 58,599(1980 IntroductionIn this report, we will study the unsubstituted ring Conformational analysis of heterocyclic systems did not begin (1, 2) until well after the birth of classical conformational analysis (3). The uncertainty associated with the extension of well accepted tools of analysis for classical conformational systems, to unknown systems, is the main cause of this late development. For any new heterocyclic system under study, the obtained informations must be cross-checked by the use of different methods. The and in the next report (4), we will consider the effect of perturbations in this system due to the presence of substituents at positions 3, 4, and 5. This first paper tentatively answers the questions: is the heterocycle planar or puckered? If indeed the ring is puckered, to what extent is it, compared with its alicyclic homologs? Do the experimental results allow us to affirm that a pseudo-rotation process exists in this ring system? following reports illustrate this approach. The purResults and Discussion pose of this paper is to define the conformational properties of the nonsymmetric monounsaturated Obseruarion and Eualuation ofthe Degree ofpuckering heterocyclic system, namely thiazolidine-2-thione of the Thiazolidine-2-thione Ring (TH-2-33) 8.' H Nuclear Magnetic Resonance -JVi, -Application of the Simplified Karplus Equation 'Revision received November 12, 1979. he-analysis of the 'N nmr spectra (Table 1) torsional angle cp between the two corresponding vicinal carbon atoms.In the case of a planar ring in TH-2-TH: The abnormally large value for 180" (6-8) rules out the possibility of a planar conformation for the TH-ZTH ring.'N Nuclear Magnetic Resonance -JYi, -The Use of Lambert's R-ualue Method Assuming a puckered ring, thiazolidine-2-thione exists in a rapidly interconverting equilibrium mainly between two energetically equivalent conformations:The $I-CLCC5-S torsional angle cp, can be evaluated (Lambert's R-value method (9)) using the ratio of the experimental vicinal coupling constant values in the CH,-CH, fragment: i.e."tl~ere appears to be no theoretical reason to preclude applications to all common and medium rings" (9). In the TH-2-TH case, R = 0.84, i.e. cp, = 41"; therefore Lambert's R-value implies a significant puckering of the ring as in the cyclopentane (10) and dioxolane cases (1 1). 'H Nuclear Magnetic Resonance -2JHjH5, and J, , , , , Values In the series of 4-and 5-alkyl-substituted (Me, Et, iPr, tBu) TH-2-TH derivatives, the 2JH,,,r or 2J,j,j, values vary in a continuous and coherent way (4). However, substituent electronegativities vary only slightly along the series; thus the main factor which induces deviations in the J,,, values in the X-CH, fragment is the variation of the dihedral angle between the C-H bonds and the "lone-pairs orbitals" of the heteroatom x (12). The observed change in the J,,,, values in the alkylated series was therefore assigned to conformational modifications of the ring (4): that establishes the mobility of the thiazol...

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“…However, when electron pairs or polar bonds are present there is usually a strong preference for the gauche conformation. Examples of this include 2-haloethanols [2], propyl halides [3], 1,2-dimethoxyethane [4], and many other compounds.…”

Section: Introductionmentioning

confidence: 99%

Microwave Spectrum of 1-Butene Oxide

Ljunggren

Mjöberg

Bäckvall

1978

Zeitschrift Für Naturforschung A

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The microwave spectrum of 1-butene oxide in the gas phase has been studied in the frequency region 18.0-39.0 GHz. The spectrum observed arose from a rotamer with a dihedral H-C2-C3-C4 angle of 59° ± 1°. In addition to several ^-branch progressions the spectrum contained several long perpendicular RP and PR progressions. However, of the ground state lines, only the inter mediate PR transitions showed internal rotation splittings that could be resolved to yield a barrier height of 3.02 kcal mol-1. The value derived from the line splittings of the first excited methyl torsional state was slightly higher (3.17 kcal mol-1) but must be regarded as being less reliable. The components of the dipole moment, the rotational constants, and the quartic and sextic centrifugal distortion coefficients for the ground state and three vibrationally excited states were determined.

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Conformational analysis in saturated heterocyclic compounds

Cited by 167 publications

References 45 publications

Synthesis and conformational analysis of 2-arylseleno-1,3-dithianes. Crystal and molecular structure of 2-(4-methoxyphenylseleno)- and 2-(4-trifluoromethylphenylseleno)-1,3-dithiane

Synthesis and conformational analysis of 2-arylseleno-1,3-dithianes. Crystal and molecular structure of 2-(4-methoxyphenylseleno)- and 2-(4-trifluoromethylphenylseleno)-1,3-dithiane

Part I. Conformational analysis of thiazolidine-2-thione

Microwave Spectrum of 1-Butene Oxide

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