<p>Solvolysis reactions of a range of tertiary substrates in largely aqueous solvents were studied in such respects as β-deuterium kinetic isotope effects, linear free energy relationships and stereochemistry.</p><p>Solvolysis of the fluorene derivatives 9-methyl–9-(2´-X-2´-propyl)fluorene (<b>1-X,</b> X = Cl, Br, OOCCF<sub>3</sub>) involves a very short-lived carbocation intermediate. The fraction of alkene is increased by addition of general bases, which can be expressed by a Brφnsted parameter β = 0.07. The kinetic deuterium isotope effects vary with solvent composition in a way which is not consistent with a common carbocation intermediate which has time to choose between dehydronation and addition of a solvent water molecule. </p><p>In the absence of bases, the reaction of 4-chloro-4-(4´-nitrophenyl)pentan-2-one (<b>2-Cl</b>) proceeds through a short-lived carbocation intermediate yielding 4-(4´-nitrophenyl)-2-oxopent-4-ene (<b>2-</b><b>t</b>-ne)as the main elimination product. Addition of acetate ion and other weak bases results in the base-promoted E2 (or E1cb) reaction to give (<i>E</i>)-4-(4´-nitrophenyl)-2-oxopent-3-ene (<b>2-</b><b>E</b>-ne) and (<i>Z</i>)-4-(4´-nitrophenyl)-2-oxopent-3-ene(<b>2-</b><b>Z</b>-ne). There is no evidence for a water-promoted E2 (or E1cb) reaction.</p><p>The stereochemistry studies of elimination from (<i>R,S</i> and <i>S,R</i>)-[1-(3´-fluoro)phenyl-2-methyl]cyclopentyl-<i>p-</i>nitrobenzoate (<b>3-PNB</b>) and its (<i>R</i>,<i>R</i> and <i>S,S</i>)isomer <b>3´-PNB</b> and (<i>R,S</i> and <i>S,R</i>)-[1´-(3´´-fluoro)phenyl-2´-methylcyclopentyl]-2,2,2-trifluoroacetate(<b>3-OOCCF</b><b>3</b>) exclude the concerted pericyclic elimination mechanism for formation of the alkene 1-(3´-fluoro)phenyl-2-methylcyclopentene(<b>3-</b><b>m</b>-ne). The effects of added thiocyanate ion and halide ions on the solvolysis reaction are discussed.</p><p>Mass spectrometry analysis showed complete incorporation of the labeled oxygen from solvent water into the product 2-hydroxy-2-phenyl-3-butene (<b>4-OH</b>), confirming that it is the tertiary carbon-oxygen bond that is broken in the acid-catalyzed solvolysis of 2-methoxy-2-phenyl-3-butene (<b>4-OMe</b>). The mechanism for the dominant formation of the less stable <b>4-OH</b> is discussed.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-2565 |
| Date | January 2002 |
| Creators | Zeng, Xiaofeng |
| Publisher | Uppsala University, Organic Chemistry, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 743 |
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