Consequences of Strain for the Structure of Aliphatic Molecules

Rüchardt, Christoph; Beckhaus, Hans‐Dieter

doi:10.1002/anie.198505293

Cited by 58 publications

(25 citation statements)

References 65 publications

(13 reference statements)

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“…The capturing of the oct-1-yl radical by the persistent radical TEMPO (36) at 208 is slower by one order than diffusion rate and shows E A ¼ 1.8 AE 0.9 kcal mol À1 [42]. When sterically demanding substituents are introduced in ethane, the central bond is widened and loses energy, as systematic studies by Rüchardt et al revealed [43]. Whether the recombination of the strained radicals has to overcome an activation barrier could not be established with certainty.…”

Section: Methodsmentioning

confidence: 94%

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Mulzer

Huisgen

Arion

et al. 2011

Helvetica Chimica Acta

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Dedicated to Paul von Ragué Schleyer, friend and mentor, on the occasion of his 80th birthday Kinetic measurements for the thermal rearrangement of 2,2-diphenyl-1-[(E)-styryl]cyclopropane (22a) to 3,4,4-triphenylcyclopent-1-ene (23a) in decalin furnished DH = isom ¼ 31.0 AE 1.2 kcal mol À1 and DS = isom ¼ À 6.0 AE 2.6 e.u. The lowering of DH = by 20 kcal mol À1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (þ)-(S)-22a proceeds with DH = rac ¼ 28.2 AE 0.8 kcal mol À1and DS = rac ¼ À 5 AE 2 e.u., and is at 1508 106 times faster than the rearrangement. Seven further 1-(2-arylethenyl)-2,2-diphenylcyclopropanes 22, (E)-and (Z)-isomers, were synthesized and characterized. The (E)-compounds showed only modest substituent influence in their k rac (at 119.48) and k isom (at 159.38) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log k rac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring-opening of the preponderant s-trans-conformation of 22 gives rise to the 1-exophenylallyl radical 26 that bears the diphenylethyl radical in 3-exo-position, and is responsible for racemization. The 1-exo-3-endo-substituted allylic diradical 27 arises from the minor s-gaucheconformation of 22 and is capable of closing the three-or the five-membered ring, 22 or 23, respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum-chemical calculations by Houk et al. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate?

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Section: Methodsmentioning

confidence: 94%

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Mulzer

Huisgen

Arion

et al. 2011

Helvetica Chimica Acta

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“…The geminal H-H couplings within the CH, groups, 14-14. 5 Hz, suggest that distortions of H-C-H angles do not accompany those of C-C-C angles.…”

Section: Resultsmentioning

confidence: 91%

Conformations in solution of four 2,4,5,7‐tetramethyloctane‐4,5‐dicarboxylates: Molecular mechanics and NMR studies

Holland

Rae

Weigold

1991

Magnetic Reson in Chemistry

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Potential energy calculations (MM2), low-temperature 'H and I3C NMR spectra and 'H-'H COSY spectra are reported for four octane derivatives, the central portions of which constitute tetrasubstituted succinates. The existence of several conformers differing in stereochemistry in this central moiety is predicted by calculations and observed in low-temperature NMR. The periphery of each molecule is in an extended configuration, as shown by the existence of long-range (W-plan) couplings involving the methyl groups.

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“…It is also longer than the corresponding bonds in (Io), (Im) and (II) [1.789 (2), 1.785 (2) and 1.773 (4) A Ê , respectively]. Furthermore, comparison of the non-bonding distances clearly shows that steric repulsions like those described by Ru Ã chardt & Beckhaus (1985) cannot be a major reason for the SÐC1 bond elongation in (III). The SÐ C1 and C1ÐC2 bond orders in (II) (1.16 and 1.06, respectively) and (III) (1.12 and 1.02, respectively) are smaller than their analogues observed in the stable polymorph (Im) (1.26 and 1.11, respectively).…”

Section: Molecular Structure Of (Ii) and (Iii)mentioning

confidence: 82%

X-ray investigations of sulfur-containing fungicides. III. Intramolecular forces governing the conformation of a novel orthorhombic polymorph of benzoylmethyl phenyl sulfone, benzoylmethyl 4-chlorophenyl sulfone and benzoylphenylmethyl phenyl sulfone

Wolf

2001

Acta Crystallogr Sect B

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The crystal and molecular structures of three beta-ketosulfones: benzoylmethyl phenyl sulfone (I), benzoylmethyl 4-chlorophenyl sulfone (II) and benzoylphenylmethyl phenyl sulfone (III) have been investigated using X-ray analysis and quantum mechanics ab initio calculations. Compound (I) crystallizes in the monoclinic and orthorhombic crystal systems. The crystal structure of the orthorhombic polymorph has not been reported previously. At room temperature and in the presence of daylight the pale yellow orthorhombic crystals undergo transformation to the stable colourless monoclinic polymorph. Hyperconjugative sigma(S-C1) - pi(*)(C2=O3) and sigma(*)(S-C1) - pi(C2=O3) stabilization energies in benzoylmethyl phenyl sulfones are highly dependent on the central dihedral angle alpha: S-C1-C2=O3 and are largest for a gauche arrangement, as found in both crystal forms of (I). The electron density distribution in all compounds (I), (II) and (III) is significantly affected by interactions of oxygen lone pairs with non-bonding orbitals of the adjacent S-C1 and C1-C2 bonds. The latter effect is responsible for back-donation of the electron density from O atoms towards the central part of the molecule.

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Consequences of Strain for the Structure of Aliphatic Molecules

Cited by 58 publications

References 65 publications

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Conformations in solution of four 2,4,5,7‐tetramethyloctane‐4,5‐dicarboxylates: Molecular mechanics and NMR studies

X-ray investigations of sulfur-containing fungicides. III. Intramolecular forces governing the conformation of a novel orthorhombic polymorph of benzoylmethyl phenyl sulfone, benzoylmethyl 4-chlorophenyl sulfone and benzoylphenylmethyl phenyl sulfone

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