Comparison of σ and σ’ Hammett equation








for meta-directing groups (electron withdrawing group or ewg), σmeta , σpara more positive σ’. (the superscript, c, in table denotes data hammett, 1940.) ortho-para directing groups (electron donating group or edg), σ’ more positive σmeta , σpara. difference between σpara , σ’ (σpara – σ’) greater between σmeta , σ’(σmeta − σ’). expected electron resonance effects felt more @ p-positions. (σ – σ’) values can taken reasonable measurement of resonance effects.








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