LOOKING AHEAD We explain in Chapter 23 that substituents can transmit electronic information through the benzene ring when appropriately positioned. Assessments 14.55–14.59 allow us to use IR spectroscopy to discover this concept and apply it to an example (Assessment 14.60) that we study there. (•••) Justify the carbonyl stretching frequencies for a series of methoxybenzaldehydes. Specifically, why are the 2- and 4-methoxy derivatives similar to each other but different from the 3-methoxy derivative?