As we have been discussing, in an aldehyde or ketone, because oxygen is substantially more electronegative than the carbonyl carbon to which it is attached, the carbon of a carbonyl group finds itself occupying the positive end of a dipole with the oxygen occupying the negative pole. The situation for carbon in a Grignard reagent is different, however. Here, carbon is bonded to magnesium, which is less electronegative than carbon (1.2 to 2.5), so in the polar bond of carbon and magnesium within a Grignard reagent, carbon represents the negative pole. This means that while the partially positive carbonyl carbon of an aldehyde or ketone is electrophilic, the partially negative Grignard reagent carbon is nucleophilic. It naturally follows that Grignard reagents will react with aldehydes and ketones, allowing the formation of new carbon-carbon bonds.