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Anomalous Properties of NMR 1H Spectra of Haloidbenzens C6H5-Hal
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Abstract: As it was shawn previously, in a series of monosubstituted benzenes the halogen atoms as substituents worsen correlation dependence of para-protons chemical shifts δpН on Brown\'s para-constants σ+p. Point of halogens atoms are remoted at a fairly large distance from the straight line, built for 22 substituent\'s points (including halogens atoms), which has correlation coefficient R = 0.966. If we consider the halogen atoms as a separate group of substituents, the R value for diagram for remaining 18 compounds increases to 0.989. We have introduced for halogen substituents the conception of virtual "spectral Brown\'s para-constants", marked σ+p,sp.. With the aim to calculate σ+p,sp. up to 0.05, the point of halide atoms in diagram are moved horizontally to their intersection with a line built for the remaining 18 compounds. Dropping perpendiculars to the x-axis, we obtain the virtual value σ+p,sp.. σ+p,sp values of all 18 considered substitutes (except Ph and COOH), up to 0.10 coincide with the values ​​of the experimental Brown\'s para-constants σ+p. The difference (σ+p,sp.- σ+p) for halogen substituents is from -0.20 (for iodine) to -0.50 (for fluorine). It is suggested that the "spectral Brown\'s para-constants" σ+p,sp. show the maximum capacity of substituents to conjugate with the reaction center. We tried to justify the decision to consider halogen atoms as a separate group of substituents. The δiН dependences on the number of chemical bonds between the substituent and considered proton are presented graphically. It was found that the substances with electron-donating substituents (other than bromo- and iodobenzene) give graphics in the form of "mountain", which is located below the straight line of benzene ("benzene\'s line"), and the electron-withdrawing substituents give the graphics in the form of "pit", which is located above the "benzene\'s line". Graphics of bromobenzene and iodobenzene instead of the expected form of "low mountain" which located below the "benzene\'s line" and in its vicinity, due to unexplained upfield shift of δmН values ​​have anomalous "very deep pit" form, which is located above and below the "benzene\'s line", "punching" it. Also we discuss some other unexplained properties of halogen elements.