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Ab initio calculation of NMR shielding in phosphaalkenes X—PCY 2
Author(s) -
Rozhenko A. B.,
Schoeller W. W.,
Povolotskii M. I.
Publication year - 1999
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199908)37:8<551::aid-mrc503>3.0.co;2-3
Subject(s) - chemistry , chemical shift , electromagnetic shielding , excited state , ab initio , atomic orbital , carbon 13 nmr , computational chemistry , analytical chemistry (journal) , atomic physics , stereochemistry , organic chemistry , physics , nuclear physics , quantum mechanics , electron
31 P and 13 C chemical shielding values, σ iso , were calculated for a series of phosphaalkenes X—PCY 2 with a variety of substituents such as XH, CH 3 , F, Cl, Br, OH, NH 2 , PH 2 , SiH 3 , CN and YH, CH 3 , NH 2 , SiH 3 , using the GIAO procedure at the RHF/6–311 + G(d,p) and RHF/6–311 + G(2d,2p) levels. The trends governing the variation of the geometric parameters and the natural charges and Wiberg indices are discussed. The contributions of the various molecular orbitals in 31 P and 13 C chemical shielding in the phosphaalkene H—PCH 2 and ethylene, respectively, were compared. The 31 P chemical shielding variation was determined by mixing of the ground and excited states. Good correlations were found between the experimentally measured δ C and δ P values in the series X′—PC(SiMe 3 ) 2 and those calculated for the series X—PC(SiH 3 ) 2 , but on average the calculated 31 P chemical shifts seem to be overestimated. A comparison with the calculated data (at the same level) for X—PC(SiMe 3 ) 2 indicates only a partial improvement. The 13 C chemical shifts in phophaalkenes correlate within the subseries X—PCH 2 , X—PC(CH 3 ) 2 and X—PC(SiH 3 ) 2 with the charge variation at the corresponding carbon atom, reflecting the X—(PC) π‐mesomeric interactions. The absence of the corresponding correlation with all phophaalkenes investigated manifestates limited validity of this generally used approach. Copyright © 1999 John Wiley & Sons, Ltd.