Physical image vs structure relation: part 12 – structure of 2,2,5,5‐tetramethyl‐dihydro‐furan‐3‐one oxime and its protonated forms through isomerization and NMR spectra |
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Authors: | Ryszard B Nazarski |
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Institution: | Department of Organic Chemistry, Institute of Chemistry, University of ?ód?, Narutowicza 68, 90‐136 ?ód?, PolandDepartment of Organic Chemistry, University of ?ód?, Narutowicza 68, 90‐136 ?ód?, Poland.=== |
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Abstract: | The study of an isomeric A / B mixture of the title oxime 1 , by photolytic or thermal E,Z‐isomerization and NMR measurement including 1H{1H}‐NOE difference spectra, led to assignment of the E configuration to its predominating form A . The 1H/13C data were interpreted in terms of steric overcrowding of both forms, especially of the thermolabile photoproduct B . Four classical (empirical) NMR methods of elucidating the oxime geometry were critically tested on these results. Unexpected vapor‐phase photoconversion A → B in the window glass‐filtered solar UV and spectroscopic findings on their protonated states were discussed, as well. The kinetically controlled formation of the N‐protonated species (Z)‐ 5 + was proved experimentally. In addition, some 1H NMR assignments reported for structurally similar systems were rationalized ( 3 and 4 ) or revised ( 1 and 7–9 ) with the GIAO‐DFT(B3LYP) and/or GIAO‐HF calculational results. Copyright © 2007 John Wiley & Sons, Ltd. |
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Keywords: | gas‐phase photoreactions E/Z‐isomerization solar UV protonated oximes solvent effects nuclear Overhauser effect LIS analysis GIAO method |
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