Electronic Structure of Tri‐<i>tert</i>‐butylcyclopropenyl

Schreiner, Kurt; Berndt, A.

doi:10.1002/anie.197606981

Cited by 13 publications

(5 citation statements)

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“…However, below 70 K the ESR spectrum is consistent with a π-radical having C 2 v symmetry and oscillating between an elongated and a compressed pentagon. − The ESR spectrum of the trimethylcyclopropenyl radical ( 451 ), generated by photolysis of di- tert -butyl peroxide in the presence of1,2,3-trimethylcyclopropene, shows it to be an equilibrating mixture of three equivalent σ-radicals at 240 K in cyclopropane and to be a localized σ-radical at 113 K in propane . Parallel phenomena are observed with the tri- tert -butylcyclopropenyl radical , The 2,3-di- tert -butyl-1-(3,5-di- tert -butylphenyl)cyclopropenyl radical has a π-structure, presumably because of the extensive benzylic delocalization …”

Section: Computational Studies and Esr Considerationsmentioning

confidence: 95%

“…183 Parallel phenomena are observed with the tri-tert-butylcyclopropenyl radical. 184 Calculations suggest that a three-electron π-cyclopropenyl radical would be antiaromatic. 185,186 The 2,3-di-tert-butyl-1-(3,5-di-tert-butylphenyl)cyclopropenyl radical has a π-structure, presumably because of the extensive benzylic delocalization.…”

Section: Computational Studies and Esr Considerationsmentioning

confidence: 99%

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Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

et al. 1997

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ContentsI. Introduction 3273 II. Rearrangements 3275 A. β-(Acyloxy)alkyl Rearrangement 3275 1. Esters 3275 2. Lactones 3280 3. Thiocarbonyl Esters 3280 B. β-(Phosphatoxy)alkyl Rearrangement 3282 C. β-(Nitroxy)alkyl and β-(Sulfonatoxy)alkyl Rearrangements 3285 D. (Acyloxyalkyl)silyl Radical Rearrangement 3285 III. Fragmentation Reactions 3286 A. β-(Acyloxy)alkyl Radicals and Their Thiocarbonyl Analogues 3286 B. β-(Phosphatoxy)alkyl Radicals 3288 1. Anaerobic Conditions 3288 2. Aerobic Conditions 3293 C. β-(Sulfonatoxy)alkyl and Related Radicals 3294 IV. Mechanism 3294 A. β-(Ester)alkyl Radicals Susceptible to Neither Rearrangement Nor Fragmentation 3294 B. Fragmentation Reactions 3295 C. Rearrangement Reactions 3295 1. Noncage Dissociative Pathways 3296 2. Stepwise Pathways via Five-Membered Cyclic Intermediate Radicals 3296 3. Use of Isotopic and Stereochemical Labeling as Probes of Mechanism 3296 4. Quantitative Structure Activity Relationships 3298 5. Computational Studies and ESR Considerations 3299 V. Overview of β-(Ester)alkyl Radical Reactions 3303 VI. Related Reactions Involving Radical C−O Bond Shift and Cleavage 3305 A. Rearrangement and Fragmentation of β-Hydroxyalkyl Radicals 3305 B. Schenck or Allylperoxy Radical Rearrangement 3307 C. β-(Vinyloxy)alkyl to 4-Ketobutyl Rearrangement 3308 VII. Acknowledgments 3309 VIII. References 3309 Scheme 6

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Section: Computational Studies and Esr Considerationsmentioning

confidence: 95%

Section: Computational Studies and Esr Considerationsmentioning

confidence: 99%

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

et al. 1997

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“…[212][213]73.0;H,5.65;N,16.8. CZoH18N,0 requires (2 H,d,7.08 (2 H,t,J7.4,7.54 (2 H,d,J 6.9,7.63 (4 H,d,J 8.0,; m/z 331 (1 l%), 330 (M*+, 79, 223 (17), 196 (lo), 195 (lo), 107 (21), 104 (loo), 91 (1 l), 77 (99). Further elution yielded l-benzylidene-2,5-diphenylcarbonohydrazide 8a4 (R, = 0.09; 410 mg, 12%) as colourless prisms from ethanol, m. 7.3,6.83 (2 H,d,J 8.4,7.16 (2 H,dd,7.20 (1 H, s, CH=N), 7.25 (2 H, d, J 7.7,2-, 6-H in 2-Ph), 7.49 (1 H,t,J 7.4,7.58 (2 H,dd,7.67 (1 H,d,J 2.0, (2 H, 3-, 5-H in PhCH), 9.54 (1 H,d,; m/z 331 (19%), 330 (M", 92), 223 (18), 197 (20), 196 (42), 195 (36), 120 (20), 107 (22), 106 (19), 93 (29), 92 (23), 78 (12), 77 (loo).…”

Section: Methodsmentioning

confidence: 99%

Verdazyls. Part 33. EPR and ENDOR studies of 6-oxo- and 6-thioxoverdazyls. X-Ray molecular structure of 1,3,5-triphenyl-6-oxoverdazyl and 3-tert-butyl-1,5-diphenyl-6-thioxoverdazyl

Neugebauer

Fischer

Krieger

1993

J. Chem. Soc., Perkin Trans. 2

104

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A range of 6-oxoverdazyls 2b–h and 6-thioxoverdazyls 3a–c and 3e–h has been directly prepared by dehydrogenation of the corresponding 1, 4, 5, 6-tetrahydro-1, 2, 4, 5-tetrazin-3(2H)-ones 5b–h and thiones 7a–c and 7e–hwith lead dioxide, potassium hexacyanoferrate (III), or bis(4-methylphenyl)-aminyl. X-Ray analyses reveal a nearly planar verdazyl framework for the oxoverdazyl 2a, whereas the thioxoverdazyl 3ftakes on a flat boat conformation. In the latter, owing to the bulky sulfur the N-phenyl groups are considerably twisted out of the plane of the verdazyl ring. Electronic absorption spectra of the deeply coloured radicals exhibit characteristic bands in the visible region with λmax, 1 ranging from 445 to 608 nm. EPR, ENDOR and 2H NMR studies have led to a complete analysis and full assignment of all hyperfine coupling constants. The π-SOMO of 6-oxo-2 and 6-thioxo-verdazyls 3, having nodes at C(3) and C(6), is mainly confined to the nitrogens of the verdazyl ring. Spin delocalization into the N-phenyl groups is reduced, particularly in the 6-thioxoverdazyls, owing to the large torsion angle about the N–C(phenyl) bond

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“…Takada and Ohno also published an ab initio CI calculation on the electronic structure of C3H3 [6]. The most recent ab initio calculations on the molecular structure and vibrational spectrum of C3H3 were performed by Xie et al [7], and Lee et al [8], Cyclopropenyl free radical, the simplest member of the series of fully conjugated cyclic radicals, has been the subject of experimental [9][10][11][12][13] and theoretical studies [4,[14][15][16][17][18][19][20],…”

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confidence: 99%

A Theoretical Study of Monosubstituted Cyclopropenyl System

Yahya

Khalil

1992

Zeitschrift Für Naturforschung A

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MONDO-Forces calculations have been performed, with complete optimization of geometry on X-cyclopropenyl system (cations, radicals and anions), where X is H, O", OH, CH 3 , CN, N0 2 , F and CF 3 . All substituents prefer planar structure when substituted on both cations and radicals, while they prefer pyramidal structure in the case of anions except CF 3 . The substituents O", OH and F act as electron releasing, while CHO, N0 2 and CF 3 act as electron withdrawing when substituted on cyclopropenyl system. CH 3 and CN show amphielectronic behaviour. They act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand. In the case of cations and radicals, all substituents were found to increase the vicinal bonds and decrease the distal bonds and bond angles to which the substituent is attached. For anions the substitutents show no such regularity because the substituents are out of the three-membered ring plane. All substituents increase the stability of the cyclopropenyl system except CF 3 in the case of the cation.The cyclopropenyl cation is the smallest aromatic molecule which has two ^-electrons and satisfies the Hückel 4 n + 2 rule. The electronic structure is of great interset since the molecule is highly strained but despite of this the ion is stable in the form of salts, e. g. C 3 H 3 • SbCl^, and also in polar solvents [1]. D 3h configuration of the ion is indicated by its IR and NMR spectra [1], Allen has reported a structural analysis for two cyclopropenyl cation derivatives based upon Xray crystallographic data [2]. Clark carried out ab initio LCAO SCF MO Calculations on both C 3 H 3 + and C3H3 and discussed the aromaticitiy and antiaromaticity [3]. Ha et al. reported an ab initio LCAO SCF MO investigation on C 3 H 3 + , C 3 Hj and C 3 H 3~ and discussed the geometry and stability of these species [4j. Random et al. aiso carried out ab initio calculations on C3H3 using STO-3G and 6-31G and obtained the equilibrium structure of the ion [5]. Takada and Ohno also published an ab initio CI calculation on the electronic structure of C3H3 [6]. The most recent ab initio calculations on the molecular structure and vibrational spectrum of C3H3 were performed by Xie et al. [7], and Lee et al. [8], Cyclopropenyl free radical, the simplest member of the series of fully conjugated cyclic radicals, has been the subject of experimental [9-13] and theoretical studies [4,[14][15][16][17][18][19][20],The theoretical work by Chipman and Miller [20] predicts an ethylenic structure of C s symmetry as the lowest energy form. The hydrogen atom at the apex of the isoceles triangle is bent substantially out of the ring plane. The allylic structure, which satisfies the Jahn-Teller theorem, is predicted to be 5 kcal/mole higher in energy. Experimental work by Closs and Redwine [13] support the C s structure and rules out the allylic structure. There is no experimental information on the properties of the neutral radical, so it is necessary to resort to theoretical studies.The cyc...

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Electronic Structure of Tri‐tert‐butylcyclopropenyl

Cited by 13 publications

References 8 publications

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

Verdazyls. Part 33. EPR and ENDOR studies of 6-oxo- and 6-thioxoverdazyls. X-Ray molecular structure of 1,3,5-triphenyl-6-oxoverdazyl and 3-tert-butyl-1,5-diphenyl-6-thioxoverdazyl

A Theoretical Study of Monosubstituted Cyclopropenyl System

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