Assessment of substituent effects for ortho-nitrobenzenes and 2,4-dinitrobenzenes by IR and 17O NMR spectroscopy

• Published in: Journal of molecular structure Vol. 382; no. 2; pp. 93 - 99
• Main Authors: Perjéssy, Alexander, Rasala, Danuta, Gawinecki, Ryszard, Boykin, David W.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.1996
• Subjects: Hydrogen bonding; Infrared spectroscopy; NMR spectroscopy; Substituent effects; Substituted nitrobenzenes; Substituent effects; Infrared spectroscopy; Substituted nitrobenzenes; NMR spectroscopy; Hydrogen bonding
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/0022-2860(96)09256-3

Natural abundance 17O NMR chemical shift data in acetonitrile and infrared stretching frequency data in chloroform for 28 ortho-substituted nitrobenzenes (series I) and for 22 2,4-dinitrosubstituted benzenes (series II) are reported. A plot of 17O NMR chemical shift data versus the infrared stretching frequency data for compounds in series I gives a graph which is interpreted as yielding two lines, one for hydrogen bonding substituents and one for non-hydrogen bonding ones. A plot of the 17O NMR chemical shift data for the 4-nitro group of series II versus the literature values for 4-substituted nitrobenzenes gave an excellent straight line with a slope which reflected an 18% reduction in substituent effects as expected due to steric inhibition of resonance. Despite this result, correlation of the data by the dual substituent parameter approach involving σ R+ indicates that resonance effects remain important. The plot of 17O NMR chemical shift data versus the infrared stretching frequency data for compounds in series II also gives a graph which is interpreted as yielding two lines, one for hydrogen bonding substituents and one for non-hydrogen bonding ones.