Genre
- Journal Article
The reactions of the singlet methylene (la) and dimethylcarbene (1b), with their diazirine precursors, diazirine (2a), and dimethyldiazirine (2b), have been studied theoretically using ab initio and density functional theory. The reaction has no activation barriers for the parent system (la + 2a) and proceeds via a reactive complex and a transition state with a small negative enthalpy of activation (Delta H-298(not equal) = -1.1 kcal mol(-1), Delta S-298(not equal) = -34.4 cal mol(-1) K-1 Delta G(298)(o) = 9.2 kcal mol(-1)) for the dimethyl derivatives (1b + 2b). The formation of N-methylene diazirinium ylides (3a,b) is exothermic by 64-80 kcal mol(-1). The isomer, 1,3-diazabicyclo[1.1.0]butane (4a), is more stable (5-12 kcal mol(-1)) than isomer 3a, but can neither be formed by direct thermal reaction of 1a with 2a nor undergo the direct rearrangement into formaldazine (5a). The rearrangement of ylides 3a,b into azines 5a,b proceeds by conrotatory C-3(-) N-1 ring opening. The predicted activation barrier of ca. 15 kcal mol(-1) for the ring opening in ylide 3b is in excellent agreement with experimental data. The formation of pyridinium ylides from carbenes and pyridine is also studied.
Univ Calif Los Angeles, Dept Chem & Biochem, Los Angeles, CA 90095 USA. Univ Prince Edward Isl, Dept Chem, Charlottetown, PE C1A 4P3, Canada. Univ Calgary, Dept Chem, Calgary, AB T2N 1N4, Canada.; Houk, KN, Univ Calif Los Angeles, Dept Chem & Bi(TRUNCATED)
OTTAWA; RESEARCH JOURNALS, MONTREAL RD, OTTAWA, ONTARIO K1A 0R6, CANADA
NATL RESEARCH COUNCIL CANADA
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Source type: Electronic(1)
Language
- English
Subjects
- pyridinium ylide
- density functional theory
- Insertion
- ab initio MO (molecular orbital) theory
- CIS (singles configuration interaction) transition energies
- Chemistry, Multidisciplinary
- ABSOLUTE KINETICS
- LASER FLASH-PHOTOLYSIS
- ENERGIES
- diazirinium ylide