Ketones and aldehydes with electron-withdrawing substituents react more readily with diazoalkanes than those bearing electron-donating substituents (Table 2).  In addition to accelerating the reaction, electron-withdrawing substituents typically increase the amount of epoxide produced (Table 2).
The effects of substituents on the diazoalkanes is reversed relative to the carbonyl reactants: electron-withdrawing substituents decrease the rate of reaction while electron-donating substituents accelerate it.  For example, diazomethane is significantly more reactive than ethyl diazoacetate, though less reactive than its higher alkyl homologs (e.g. diazoethane).   Reaction conditions may also affect the yields of carbonyl product and epoxide product.  In the reactions of o-nitrobenzaldehyde, p-nitrobenzaldehyde,  and phenylacetaldehyde with diazomethane, the ratio of epoxide to carbonyl is increased by the inclusion of methanol in the reaction mixture.  The opposite influence has also been observed in the reaction of piperonal with diazomethane, which exhibits increased carbonyl yield in the presence of methanol.