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Dynamic 1 H NMR investigation along with a theoretical study around the C–C and C = C bonds in a particular phosphorus ylide
Author(s) -
HabibiKhorassani Sayyed Mostafa,
Maghsoodlou Malek Taher,
Ebrahimi Ali,
Mohammadi Marzyeh,
Shahraki Mehdi,
Aghdaei Elham
Publication year - 2012
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.3029
Subject(s) - chemistry , single bond , kinetic energy , carbon 13 nmr , computational chemistry , bond length , ab initio , double bond , ylide , molecular geometry , crystallography , stereochemistry , molecule , organic chemistry , crystal structure , alkyl , physics , quantum mechanics
In the present work, the dynamic 1 H NMR effects were investigated at variable temperatures within a particular phosphorus ylide involving a 2‐benzoxazolinone around the carbon–carbon single bond and also partial carbon–carbon double bond in two Z ‐ and E ‐rotational isomers. Activation and kinetic parameters including ΔH ≠ , ΔG ≠ , ΔS ≠ and E a were determined in accord with the dynamic 1 H NMR data for three rotational processes. In addition, theoretical studies based upon rotation around the same bonds were investigated using ab initio and DFT methods at the HF/6‐31G(d,p) and B3LYP/6‐31G(d,p) levels of theory. Theoretical activation and kinetic parameters including ΔH ≠ , ΔG ≠ , ΔS ≠ and E a were calculated at 298 K and experimental temperatures for five rotational processes. These results (experimental and theoretical), taken together, indicate that the rotational energy barrier around the C = C double bond was considerably high and the observation of the two rotational isomers was impossible (seen as a single isomer) at the high temperatures, in this case rotation around the C = C bond was too fast on the NMR time scale. When the temperature was relatively low, the rate of rotation was sufficiently slow; therefore, observation of the two Z ‐ and E ‐isomers was possible. In addition, calculations at the HF/6‐31G(d,p) level of theory showed very favorable results in agreement with the experimental data on rotation around the C = C bond. While, B3LYP level using the 6‐31G(d,p) basis set was provided the reasonable data for the restricted rotations around the C–C and C–N single bond. Copyright © 2012 John Wiley & Sons, Ltd.