Transient carbocations and carbanions generated by laser flash photolysis and pulse radiolysis. [Ultraviolet radiation]
- Univ. of Notre Dame, IN (United States). Radiation Lab.
Closed-shell carbocations and carbanions have long been implicated as well-defined intermediates in ionic reaction mechanisms involving organic compounds. There is plentiful spectroscopic and other evidence for formation of stable or metastable carbocations in acidic media. Similarly, stabilized carbanions formed as a result of deprotonation mediated by a strong base in deaerated nonprotic solvents are easily recognized by their color and absorption spectra. Depending on the electronic makeup of a molecule as well as its environment (solvent), the heterolysis of an appropriate bond leading to carbocations or carbanions can be as important as homolysis producing radicals. An understanding of the structure and reactivity of carbon-centered ions is of pivotal importance to kinetics and mechanisms of organic reactions, including ionic polymerization. Resonance-stabilized carbocations and carbanions are responsible for certain photochromic phenomena (e.g., photodissociation of triphenylmethane leuco derivatives into colored ion pairs and UV-induced color changes of nitrotoluenes). Furthermore, as the present review will provide many examples, these species often constitute spectrally observable, relatively long-lived intermediates in the course of radiation--chemical charge separation. Contents include the generation of carbocations and carbanions; time-resolved detection, spectroscopic properties; ground-state electrophilic reactivity of carbocations; ground-state nucleophilic reactivity of carbanions; singlet excited-state electrophilic reactivity of carbocations; electron-transfer reactions of carbocations; electron transfer involving carbanions; and triplets of carbocations. 200 refs.
- OSTI ID:
- 6234439
- Journal Information:
- Chemical Reviews; (United States), Journal Name: Chemical Reviews; (United States) Vol. 93:1; ISSN CHREAY; ISSN 0009-2665
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400500* -- Photochemistry
ANIONS
CARBON COMPOUNDS
CARBON IONS
CATIONS
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DECOMPOSITION
DOCUMENT TYPES
ELECTROMAGNETIC RADIATION
ELECTRON TRANSFER
ENERGY LEVELS
EXCITED STATES
IONS
KINETICS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATIONS
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
REVIEWS
ULTRAVIOLET RADIATION