Determination and interrelation of bond heterolysis and homolysis energies in solution

Arnett, Edward M.; Amarnath, Kalyani; Harvey, Noel G.; Cheng, Jiang

doi:10.1021/ja00157a053

Cited by 107 publications

(63 citation statements)

References 11 publications

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“…Usually the potassium salt of the carbanion is used, and the tetrafluoroborate salt of the cation is prepared by standard methods (27)(28)(29). The solution of one of the ions is charged to the argonpurged calorimeter vessel inside the dry box and transferred to the calorimeter under argon pressure.…”

Section: Experimental Methodsmentioning

confidence: 99%

Chemical Bond-Making, Bond-Breaking, and Electron Transfer in Solution

Arnett

Amarnath

Harvey

et al. 1990

Science

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A method is described for determining heats of heterolysis, DeltaH(het), from the heats of reaction of resonancestabilized carbenium ions with carbanions in solution. These results can be converted into heats of homolysis, DeltaH(homo), for the same bonds by combining DeltaH(het) values with electron transfer energies, deltaG(ET) (deltaG(ET) approximately deltaH(ET)), obtained from redox potentials of the reacting ions. The results provide a comprehensive tabulation of DeltaH(het), DeltaH(homo), and DeltaG(ET) values for an extended series of organic compounds and are examined in terms of their interrelationships and a number of related properties of the ions and radicals.

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Section: Experimental Methodsmentioning

confidence: 99%

Chemical Bond-Making, Bond-Breaking, and Electron Transfer in Solution

Arnett

Amarnath

Harvey

et al. 1990

Science

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“…The oxidation potentials of the catechol and hydroquinone derivatives (E ox ) were determined by using second harmonic ac voltammetry (SHACV) and the E ox values obtained are listed in Table 1 in which the HOMO energies were calculated by DFT methods at the B3LYP/6-31G* level. [33] The singlet excited-state energy (S 1 ) of [H 4 DPP]Cl 2 was determined from the fluorescence maximum (731 nm) and the absorption maximum (712 nm) in argon-bubbled CH 2 Cl 2 was 1.72 eV ( Figure S2 in the Supporting Information). [34] The triplet excited-state energy (T 1 ) was determined from the phosphorescence (838 nm) at 77 K as 1.48 eV ( Figure S3 in the Supporting Information).…”

Section: Energetics Of Petmentioning

confidence: 99%

Selective Inclusion of Electron‐Donating Molecules into Porphyrin Nanochannels Derived from the Self‐Assembly of Saddle‐Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

Kojima

Nakanishi

Harada

et al. 2007

Chemistry A European J

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A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at lambda>340 nm at room temperature) of the PNC that contains p-hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively.

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“…[8]- [13]) are given in Table 2. We have assumed that the bond energy for ' 1-methylnaphthalene derivatives is not dependent on ring ' substitution (AH0, = 85 kcal mol-'; AGO, = 77 kcal mol-I i (31)).…”

Section: Substituent Effects On Derived Thermochemical Parametersmentioning

confidence: 99%

Substituent and charge distribution effects on the redox potentials of radicals. Thermodynamics for homolytic versus heterolytic cleavage in the 1-naphthylmethyl system

Milne¹,

Wayner²,

DeCosta³

et al. 1992

Can. J. Chem.

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Can. J. Chem. 70, 121 (1992). The electrochemical oxidation and reduction potentials of a number of substituted 1-methylnaphthalenes (la-1) and 1-naphthylmethyl radicals (2a-1') as well as 2-methylnaphthalene (3) and the 2-naphthylmethyl radical (4') have been measured by cyclic voltammetry and photomodulation voltammetry. The oxidation potentials correlate with a+ (p+ = -7.1 and -8.4 for 1 and 2' respectively) while the reduction potentials correlate with a (p-= 10.1 and 13.0 for 1 and 2' respectively). The relative magnitude of the p values can be rationalized when the charge density distribution in these systems is considered. This leads to the interesting conclusion that even though a full charge is placed in the IT-system of 1 when it is oxidized or reduced, the fraction of the charge that accumulates at C, is actually less than in 2+ or 2-where only 50-70% of the charge is delocalized into the ring. A correlation between p for the redox reactions of 1 , 2', benzyl, diphenylmethyl, and cumyl and the calculated (AMI) charge density at C, is established, implying that the sensitivity of the corresponding ions to substituent effects increases as the fraction of charge at that site increases. The redox data have been used in thermochemical cycles in order to estimate the substituent effect on the homolytic, mesolytic, and heterolytic cleavage reactions of 1 and its corresponding radical ions. The implication of these results on the C-C cleavage versus deprotonation of radical cations and on the photochemical homolysis versus heterolysis of naphthylmethyl halides and-acetates is discussed.

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Determination and interrelation of bond heterolysis and homolysis energies in solution

Cited by 107 publications

References 11 publications

Chemical Bond-Making, Bond-Breaking, and Electron Transfer in Solution

Chemical Bond-Making, Bond-Breaking, and Electron Transfer in Solution

Selective Inclusion of Electron‐Donating Molecules into Porphyrin Nanochannels Derived from the Self‐Assembly of Saddle‐Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

Substituent and charge distribution effects on the redox potentials of radicals. Thermodynamics for homolytic versus heterolytic cleavage in the 1-naphthylmethyl system

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