• 제목/요약/키워드: Frontside-attack

검색결과 43건 처리시간 0.02초

Kinetics and Mechanism of the Aminolysis of Anilino Thioethers with Benzylamines in Acetonitrile

  • Oh, Hyuck-Keun;Lee, Jae-Myun;Sung, Dae-Dong;Lee, Ik-Choon
    • Bulletin of the Korean Chemical Society
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    • 제25권4호
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    • pp.557-559
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    • 2004
  • The aminolyses of anilinothioethers $(C_6H_5N(CH_3)CH_2SC_6H_4Z)$ in acetonitrile with benzylamines $(XC_6H_4CH_2NH_2)$ have been investigated. The rates are much lower in acetonitrile than in methanol (with aniline). The Bronsted ${\beta}_X$ values are similar but ${\beta}_Z$ values are smaller compared to those for the reactions in MeOH with anilines. The large negative ${\rho}_{XZ}({\cong}-0.8$, after correction for fall-off) value is interpreted to indicate a frontside attack $S_N2$ mechanism, in which the two oppositely changed reaction centers in the TS, $-N^{{\delta}+}{\cdots}S^{{\delta}-}-$, are in close vicinity increasing the interaction between nucleophile and leaving group. The inverse secondary kinetic isotope effects ($k_H/k_D$ < 1.0) are observed with deuterated benzylamines $(XC_6H_4CH_2ND_2)$.

Pyridinolysis of O,O-Diphenyl S-Phenyl Phosphorothiolates in Acetonitrile

  • Adhikary, Keshab Kumar;Lumbiny, Bilkis Jahan;Kim, Chan-Kyung;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • 제29권4호
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    • pp.851-855
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    • 2008
  • The reactions of O,O-diphenyl Z-S-phenyl phosphorothiolates with X-pyridines have been studied kinetically in acetonitrile at $35.0{^{\circ}C}$. The Hammett plots for substituent (Z) variations in the leaving group (log $k_2$ vs. $\sigma$ Z) are biphasic concave downwards with breaks at Z = H. The large magnitudes of ${\rho}X(\rho_{nuc})$, ${\beta}X(\rho_{nuc})$, and the cross-interaction constant, $\rho$XZ, suggest frontside nucleophilic attack toward the leaving group. The sign reversal of $\rho$Z from positive in $\sigma$ Z $\leq$ 0 to negative in $\sigma$ Z $\geq$ 0 is interpreted as the change in mechanism from concerted to stepwise with rate-limiting expulsion of the leaving group. The anomalous negative sign of $\rho$ Z for leaving groups with electron-withdrawing substituents is interpreted as the intramolecular ligand exchange process of the leaving group from the equatorial position in the intermediate to the apical position in the TS.

Anilinolysis of Diphenyl Thiophosphinic Chloride and Theoretical Studies on Various R1R2P(O or S)Cl

  • Dey, Nilay Kumar;Han, In-Suk;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • 제28권11호
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    • pp.2003-2008
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    • 2007
  • The aminolysis of diphenyl thiophosphinic chloride (2) with substituted anilines in acetonitrile at 55.0 oC is investigated kinetically. Kinetic results yield large Hammett ρX (ρnuc = ?3.97) and Bronsted βX (βnuc = 1.40) values. A concerted mechanism involving a partial frontside nucleophilic attack through a hydrogen-bonded, four-center type transition state is proposed on the basis of the primary normal kinetic isotope effects (kH/kD = 1.0-1.1) with deuterated aniline (XC6H4ND2) nucleophiles. The natural bond order charges on P and the degrees of distortion of 42 compounds: chlorophosphates [(R1O)(R2O)P(=O)Cl], chlorothiophosphates [(R1O)(R2O)P(=S)Cl], phosphonochloridates [(R1O)R2P(=O)Cl], phosphonochlorothioates [(R1O)R2P(=S)Cl], chlorophosphinates [R1R2P(=O)Cl], and chlorothiophosphinates [R1R2P(=S)Cl] are calculated at the B3LYP/ 6-311+G(d,p) level in the gas phase.

Kinetics and Mechanism of the Pyridinolysis of Diethyl Isothiocyanophosphate in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • 제33권3호
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    • pp.1042-1046
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    • 2012
  • The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of diethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles exhibit the two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with rate-limiting expulsion of the isothiocyanate leaving group from a trigonal bipyramidal pentacoordinated intermediate. The relatively large ${\beta}_x$ values with more basic and less basic pyridines imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb.

Kinetics and Mechanism of the Pyridinolysis of Diisopropyl Chlorothiophosphate in Acetonitrile

  • Hoque, Md. Ehtesham Ul;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • 제33권10호
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    • pp.3203-3207
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    • 2012
  • The nucleophilic substitution reactions of diisopropyl chlorothiophosphate (5) with X-pyridines have been kinetically studied in MeCN at $35.0^{\circ}C$. The Hammett and Br$\ddot{o}$nsted plots for the substituent X variations in the nucleophiles show biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 5 exhibits great negative deviation from the Taft plot. A concerted $S_N2$ mechanism is proposed involving a change of the attacking direction of the X-pyridines from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines.

Kinetics and Mechanism of Anilinolyses of Aryl Methyl and Aryl Propyl Chlorothiophosphates in Acetonitrile

  • Barai, Hasi Rani;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • 제35권9호
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    • pp.2797-2802
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    • 2014
  • Nucleophilic substitution reactions of Y-aryl methyl (8) and Y-aryl propyl (10) chlorothiophosphates with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at $55.0^{\circ}C$. A concerted mechanism is proposed for 8 based on the negative ${\rho}_{XY}$ (= -0.23) value, while a stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed for 10 based on the positive ${\rho}_{XY}$ (= +0.68) value. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are 0.89-1.28 and 0.62-1.20 with 8 and 10, respectively. Primary normal and secondary inverse DKIEs are rationalized by a frontside attack involving hydrogen bonded, four-center-type transition state and backside attack involving in-line-type transition state, respectively.

Kinetics and Mechanism of the Anilinolysis of Aryl Ethyl Isothiocyanophosphates in Acetonitrile

  • Barai, Hasi Rani;Adhikary, Keshab Kumar;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • 제34권6호
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    • pp.1829-1834
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    • 2013
  • The nucleophilic substitution reactions of Y-aryl ethyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines were investigated kinetically in acetonitrile at $75.0^{\circ}C$. The free energy relationships with X in the nucleophiles exhibited biphasic concave downwards with a break point at X = H. A stepwise mechanism with rate-limiting bond formation for strongly basic anilines and with rate-limiting bond breaking for weakly basic anilines is proposed based on the negative and positive ${\rho}_{XY}$ values, respectively. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) changed gradually from primary normal with strongly basic anilines, via primary normal and secondary inverse with aniline, to secondary inverse with weakly basic anilines. The primary normal and secondary inverse DKIEs were rationalized by frontside attack involving hydrogen bonded, four-center-type TSf and backside attack involving in-line-type TSb, respectively.

Kinetics and Mechanism of Anilinolyses of Ethyl Methyl, Ethyl Propyl and Diisopropyl Chlorothiophosphates in Acetonitrile

  • Barai, Hasi Rani;Hoque, Md. Ehtesham Ul;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • 제34권12호
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    • pp.3811-3816
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    • 2013
  • Nucleophilic substitution reactions of ethyl methyl (2), ethyl propyl (4) and diisopropyl (7) chlorothiophosphates with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at $55.0^{\circ}C$. A concerted mechanism is proposed based on the selectivity parameters. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are secondary inverse ($k_H/k_D=0.66-0.99$) with 2, primary normal and secondary inverse ($k_H/k_D=0.78-1.19$) with 4, and primary normal ($k_H/k_D=1.06-1.21$) with 7. The primary normal and secondary inverse DKIEs are rationalized by frontside attack involving hydrogen bonded, four-center-type transition state, and backside attack involving in-line-type transition state, respectively. The anilinolyses of ten chlorothiophosphates are examined based on the reactivity, steric effect of the two ligands, thio effect, reaction mechanism, DKIE and activation parameter.

Kinetics and Mechanism of the Pyridinolysis of Diisopropyl Thiophosphinic Chloride in Acetonitrile

  • Hoque, Md. Ehtesham Ul;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • 제32권12호
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    • pp.4387-4391
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    • 2011
  • The kinetic studies on the pyridinolysis of diisopropyl thiophosphinic chloride have been carried out in acetonitrile at $55.0^{\circ}C$. The free energy correlations for substituent X variations in the X-pyridines are biphasic concave upwards with a break point at X = 3-Ph. A concerted SN2 mechanism is proposed with a change of the attacking direction of the X-pyridine from a frontside attack for the strongly basic pyridines to a backside attack for the weakly basic pyridines. The factors to determine the rates and thio effects on the rates for the pyridinolyses of thiophophinic chloride, chlorothiophosphate, phosphinic chloride, phosphonochloridothioate, and chlorophosphate systems are briefly reviewed on the basis of the magnitude of the positive charge of the reaction center P atom and steric effects of the two ligands.

Kinetics and Mechanism of the Pyridinolysis of Dimethyl Isothiocyanophosphate in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • 제33권7호
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    • pp.2260-2264
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    • 2012
  • The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of dimethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Br$\ddot{o}$nsted plots for substituent X variations in the nucleophiles exhibit two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with a rate-limiting expulsion of the isothiocyanate leaving group from the intermediate. The relatively large ${\beta}x$ values imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb. The steric effects of the two ligands play an important role to determine the pyridinolysis rates of isothiocyanophosphates.