Distonic radical cations

Yates, Brian F.; Bouma, Willem J.; Radom, Leo

doi:10.1016/s0040-4020(01)88084-4

Cited by 174 publications

(76 citation statements)

References 82 publications

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“…Thus, the radical cation cleavage (Scheme 1, step 4) occurs rapidly enough to compete 3~h e nomenclature in this area has not been fully defined. We recognize a difference between 1 ,n-radical ions and distonic radical ions (9). Distonic radical ions are coordinatively saturated at the ionic site and are not available by one-electron transfer involving a stable precursor without extensive rearrangement.…”

Section: Introductionmentioning

confidence: 91%

“…We have studied the photosensitized (electron transfer) reactions of [8][9][10][11] (and 15) under conditions identical with those used previously in reactions [ l ] and [2]. are cyclic analogs of 1 and 2.…”

Section: Introductionmentioning

confidence: 99%

“…For example, 2-(2,2-diphenylethy1)-1,3-dioxalane gives a good yield of diphenylmethane and 2-methoxy-l,3-dioxalane under these conditions (D. R. Arnold 9 trans SCHEME 3. The synthesis of 2-methoxy-1-phenylindane (9). (a) 9-BBN, THF, reflux; NaOH, HzOz, aq.…”

Section: Introductionmentioning

confidence: 99%

“…In the presence of nucleophiles, reaction proceeds as with acyclic analogues. For example, the acetals 22 and 29 are formed in high yield in reactions [8] and [9]. The bond cleavage process requires orbital overlap with the SOMO.…”

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1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations

Arnold¹,

Fahie²,

Lamont³

et al. 1987

Can. J. Chem.

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. Can. J. Chem. 65, 2734Chem. 65, (1987.The photosensitized (electron transfer) reactions of 3-phenyl-2.3-dihydrobenzofuran @a), 5-methyl-3-phenyl-2,3-dihydrobenzofuran (8b), cis and trans-2-methoxy-1-phenylindane (9, cis and trans), 3,3-diphenyltetrahydrofuran (lo), and 22-diphenyl-1-methoxycyclopentane (11) have been studied using 1,4-dicyanobenzene as an electron-accepting photosensitizer and acetonitrile-methanol (3: 1) as solvent. These reaction conditions cause carbon-carbon bond cleavage of analogous acyclic P,P-diphenylethyl ethers to give products derived from the diphenylmethyl radical and the a-oxycarbocation intermediates. The purpose of this study was to determine if this reaction could be applied to five-membered cyclic derivatives to give 1,5-radical cations.The primary products from 8 a and 8b were the dehydrogenated, aromatized 3-phenylbenzofurans 140 and 14b. These products react further; continued irradiation gave the methanol adducts, cis and tmns-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a and 15b, cis and trans). The only observed reaction of the indanes (9, cis and trans) was cis-trans isomerization. Deuterium was incorporated at the bis-benzylic position of 8 and 9 when the irradiation was carried out in acetonitrilemethanol-0-d. These results are consistent with reversible deprotonation from the radical cations. 'There was no evidence for carbon-carbon bond cleavage with either 8 or 9. The relative rate, deprotonation faster than carbon-carbon bond cleavage, is explained in terms of the conformation of the bond that cleaves in relation to the singly occupied molecular orbital (SOMO) of the radical cation. Oxidation potential measurements support the conclusion that the SOMO of 8 and 9 is largely associated with the fused phenyl ring and is therefore orthogonal to the benzylic carbon-carbon bond. Irradiation of cis or trans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a, cis or trans), under these conditions, leads to cis-trans isomerization. The mechanism in this case involves the reversible loss of methanol. There is evidence that the addition of methanol to 14 involves the sensitizer radical anion -14 radical cation pair.In contrast with the fused bicyclic systems, the monocyclic tetrahydrofuran 10 and the methoxycyclopentane 11 both cleave under these conditions; the products are the expected acetals 22 and 29 formed from the intermediate 1,5-radical cations. In 10 and 11 the SOMO, which is largely associated with the diphenylmethyl moiety, can overlap with the adjacent carbon-carbon bond and cleavage occurs as in analogous acyclic systems. Both 10 and 11 are relatively stable to irradiation under conditions that are identical except with acetonitrile as solvent (without methanol). We found no evidence for cyclization of the intermediates (1,hadical cation or 1,5-diradical) into the terminal phenyl ring. DONALD R. ARNOLD, BRIAN J. FAHIE, LAURIE J. LAMONT, JACEK WIERZCHOWSKI et KENT M. YOUNG. Can. J. Chem. 65, 2734Chem. 65, (1987.Utilisant le dicyano-1,4 benzkne comme photosen...

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations

Arnold¹,

Fahie²,

Lamont³

et al. 1987

Can. J. Chem.

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“…This Table 5. more favorable structure is a distonic radical ion in which charge and electron spin are formally separated [28]. All the fragmentation pathways a -f were observed.…”

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confidence: 91%

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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Fragmentation and isomerization of ionized trimethylphosphine sulfide (CH3)3P(S): ion structures andab initio MO calculations

Keck

Tommes

1999

J. Mass Spectrom.

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EI fragmentation of trimethylphosphine sulfide (CH3 )3P(S) (1) is reported and discussed. [1]+• mainly retains the connectivity of the neutral molecule and no rearrangements to other long‐lived isomeric forms occur. However, some [1]+• ions undergo a unimolecular reaction by a [1,3]‐hydrogen shift from carbon to sulfur atom to produce the short‐lived carbon centered ylide radical [(CH3)2 (•CH2)P+ ‐SH]. Further, isomerization of the molecular ion by an [1,2]‐shift of a methyl group from phosphorus to sulfur is suggested which leads to [(CH3) 2P‐SCH3]+• . Compared to [1]+• the coordination number at phosphorus in the latter ion is reduced from four to three. Structures of fragment ions [C2 ,H6 ,P,S]+ (m/z 93), [C3,H8,P]+ (m/z 75) and [C2,H 6,P]+ (m/z 61) have been examined by collisional activation (CA) mass spectrometry. All the even‐electron ions exist with a phosphonium structure as dimethylthioxophosphonium‐ [(CH3)2P=S] + (m/z 93), dimethyl‐methylenephosphonium‐ [(CH3 )2P=CH2]+ (m/z 75), and methyl‐methylenephosphonium‐ion [(CH3 )HP=CH2]+ (m /z 61), respectively. The experimental findings are confirmed and complemented by the results of ab initio MO calculations. Copyright © 1999 John Wiley & Sons, Ltd.

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Distonic radical cations

Cited by 174 publications

References 82 publications

1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations

1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations

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

Fragmentation and isomerization of ionized trimethylphosphine sulfide (CH3)3P(S): ion structures andab initio MO calculations

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