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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
Author(s) -
Nazarski Ryszard B.
Publication year - 2007
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1167
Subject(s) - chemistry , isomerization , oxime , protonation , steric effects , furan , carbon 13 nmr , proton nmr , nmr spectra database , spectral line , computational chemistry , photochemistry , stereochemistry , medicinal chemistry , organic chemistry , ion , physics , astronomy , catalysis
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 1 H{ 1 H}‐NOE difference spectra, led to assignment of the E configuration to its predominating form A . The 1 H/ 13 C 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 1 H 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.