Formation and Stability of the 4-Methoxyphenonium Ion in Aqueous Solution

Tsuji, Yutaka; Hara, Daisuke; Hagimoto, Rui; Richard, John P.

doi:10.1021/jo202118s

Cited by 8 publications

(21 citation statements)

References 22 publications

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“…18 The procedure for dissection of the contribution of these pathways has been described in earlier studies on nucleophile addition of azide anion to X-1-Ts . 24,25 …”

Section: Discussionmentioning

confidence: 99%

“…2-(4-Methoxyphenyl)ethyl 1-[ 13 C]tosylate [ MeO-1- [α- 13 C]Ts ] [99% enrichment] and 2-(4-methylphenyl)ethyl 1-[ 13 C]tosylate [ Me-1-[α- 13 C]Ts ] [99% enrichment] were synthesized by published procedures. 24,25 …”

Section: Methodsmentioning

confidence: 99%

“…24,25 The reactions were allowed to proceed to completion at room temperature, at which time the relative yields of the nucleophile ( X-1-Nu , Nu = Br, Cl, CH 3 CO 2 , Cl 2 CHCO 2 ), water ( X-1-OH ) and trifluoroethanol ( X-1-OCH 2 CF 3 ) adducts were determined from the relative peak areas from HPLC analysis, with peak detection at 276 nm and 265 nm, for MeO-1-Y and Me-1-Y respectively, which is λ max for the respective water adducts. 24,25 It was shown in previous work that the molar extinction coefficients for products of the substitution reactions of nucleophiles and of solvent 1-(4-methoxyphenyl)ethyl derivatives and at 1-(4-methylphenyl)ethyl derivatives are the same. 6,42 …”

Section: Methodsmentioning

confidence: 99%

“…19–22 By contrast, much less is known about the rate constants for nucleophile addition to bridging phenonium ions X-2 + , which form as intermediates of nucleophilic substitution reactions at X-1-Ts (Scheme 1A). 23 We are interested in estimating absolute rate constants for nucleophile addition to the strained cyclopropyl ring of X-2 + , 24,25 and in comparing these with rate constants for nucleophile addition to classical carbocations, such as those shown in Chart 1.…”

mentioning

confidence: 99%

“…24,25 This decrease in nucleophile selectivity is substantially smaller than the decrease from k az / k s = 100 M −1 and k az / k s = 1.1 M −1 determined for MeO-3 + and Me-3 + in the same solvent, 6,33 which reflects the sharp increase in k s relative to the essentially constant value of k Nu ≈ 5×10 9 M −1 for the diffusion-limited reaction of azide anion. 2,6,33,34 These results are consistent with a small decrease in the nucleophile selectivity of X–2 + , with increasing electrophile reactivity, for reactions that are limited by the chemical barrier to nucleophile addition ( k Nu < k d ≈ 5×10 9 M −1 ).…”

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confidence: 99%

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Swain–Scott relationships for nucleophile addition to ring-substituted phenonium ions

Tsuji

Richard

2015

Can. J. Chem.

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The products of the reactions of 2-(4-methoxyphenyl)ethyl tosylate (MeO-1-Ts) and 2-(4-methyphenyl)ethyl tosylate (Me-1-Ts) with nucleophilic anions were determined for reactions in 50/50 (v/v) trifluoroethanol/water at 25°C. In many cases the nucleophile selectivity kNu/ks (M−1) for reactions of nucleophile and solvent, calculated from the ratio of product yields, depends upon [Nu−]. This demonstrates the existence of competing reaction pathways, which show different selectivities for reactions with nucleophiles. A carbon-13 NMR analysis of the products of the reactions of substrate enriched with carbon-13 at the α–carbon, X-1-[α–13C]Ts, (X = -OCH3, -Me) with nucleophilic anions in 50/50 (v/v) trifluoroethanol/water at 25°C shows the formation of X-1-[β-13C]OH, X-1-[β-13C]OCH2CF3 and X-1-[β-13C]Nu (Nu = Br, Cl, CH3CO2, Cl2CHCO2) from the trapping of symmetrical 4-substituted phenonium ion reaction intermediates X-2+. The observation of excess label in the α-position, [α-13C]/[β-13C] > 1.0, for both the water and nucleophile adducts, shows that water and anionic nucleophiles also react by direct substitution at X-1-[α-13C]Ts. The ratios of product yields, [α-13C]/[β-13C], and observed nucleophile selectivity (kNu/ks)obs were used to dissect the contribution of direct nucleophile addition at Me-1-Ts and trapping of X-2+ to the product yields. The product yields from partitioning of the intermediate gave the nucleophile selectivity kNu/ks (M−1) for X-2+. Swain-Scott plots of log (kNu/ks) are correlated by slopes of s = 0.78 and s = 0.73 for reactions of MeO-2+ and Me-2+, respectively. This shows that the sensitivity of bimolecular substitution at X-2+ to changes in nucleophile reactivity is smaller than for nucleophilic substitution at the methyl iodide. Evidence is presented that nucleophile addition to X-2+ proceeds through an “exploded” transition state.

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“…18 The procedure for dissection of the contribution of these pathways has been described in earlier studies on nucleophile addition of azide anion to X-1-Ts . 24,25 …”

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%