ISSN:
0030-4921
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
17O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para-substituted acetophenones, X—C4H6—COCH3, where X = NH2, OCH3, F, Cl, CH3, H, COCH3, CN, NO2. The 17O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σI and σR+ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρI and ρR indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π-electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λmsxn→π* values are also reported, and the role of the average excitation energy, ΔE, in determining 17O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ-electron density is the dominant feature controlling 17O SCS values.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/omr.1270211005
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