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Electrophilic Selenium Catalysis with Electrophilic N
Electrophilic Selenium Catalysis with Electrophilic N

Organic synthesis and methodology related to the malaria drug artemisinin
Organic synthesis and methodology related to the malaria drug artemisinin

... Figure 64: Initial Substrate Screening with MeCN ..................................... 121 Figure 65: Initial Substrate Screening with CH2Cl2 .................................... 122 Figure 66: Use of Electron-Rich Ethoxyacetylene ..................................... 123 Figure 67: Qualitative Scre ...
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IOSR Journal of Applied Chemistry (IOSR-JAC)
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NAME Chem 204 Spring, 1990 Final Exam FINAL EXAM: Chaps. 1
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... ? Fe(H2 O) 6 ? 2? , ?J. Chem. Phys. 120, 9473 ?2004?? to include a second compound—namely, the hexaminoferrous cation, ? Fe(NH3 ) 6 ? 2? —and several additional functionals. In particular, the present study includes the highly parametrized generalized gradient approximations ?GGAs? known as HCTH and ...
< 1 2 3 4 5 6 7 8 ... 73 >

Woodward–Hoffmann rules



The Woodward–Hoffmann rules, devised by Robert Burns Woodward and Roald Hoffmann, are a set of rules in organic chemistry predicting the barrier heights of pericyclic reactions based upon conservation of orbital symmetry. The Woodward–Hoffmann rules can be applied to understand electrocyclic reactions, cycloadditions (including cheletropic reactions), sigmatropic reactions, and group transfer reactions. Reactions are classified as allowed if the electronic barrier is low, and forbidden if the barrier is high. Forbidden reactions can still take place but require significantly more energy.The Woodward–Hoffmann rules were first formulated to explain the striking stereospecificity of electrocyclic reactions under thermal and photochemical control. Thermolysis of the substituted cyclobutene trans-1,2,3,4-tetramethylcyclobutene (1) gave only one diastereomer, the (E,E)-3,4-dimethyl-2,4-hexadiene (2) as shown below; the (Z,Z) and the (E,Z) diastereomers were not detected in the reaction. Similarly, thermolysis of cis-1,2,3,4-tetramethylcyclobutene (3) gave only the (E,Z) diastereomer (4).Due to their elegance and simplicity, the Woodward–Hoffmann rules are credited with first exemplifying the power of molecular orbital theory to experimental chemists. Hoffmann was awarded the 1981 Nobel Prize in Chemistry for this work, shared with Kenichi Fukui who developed a similar model using frontier molecular orbital (FMO) theory; because Woodward had died two years before, he was not eligible to win what would have been his second Nobel Prize for Chemistry.
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