Substituent-induced chemical shifts in 3- and 4-substituted styrenes: factor analysis of the styrene data matrix

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Abstract
The techniques of factor analysis are used to investigate a data matrix constructed from magnetic resonance parameters for seventy-five 4-substituted styrenes, α-methylstyrenes, and α-tert-butylstyrenes and 3-substituted styrenes and α-methylstyrenes (with fifteen common substituents for each series). Two substituent factors (parameters) are clearly both necessary and sufficient to predict long-range chemical shifts within experimental uncertainty. Target testing indicates that Taft's σ1 and [Formula: see text] constants are appropriate for this purpose. One additional major factor is required for each of ipso and ortho carbons and a minor factor is apparently required for meta carbons.Conclusions do not appear to be sensitive to the weighting of individual variables and the specific variables included in the data matrix. However, the use of an extensive and well-chosen substituent set is essential.

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