When will organometallics act as base or nucleophile?
Grignard is a base as well as an nucleophile. When there's a strong electron deficient group it'll attack there, when there' a very acidic group it'll attack there. For other bases it depends upon their relative basicity and nucleophilicity. BAsicity is thermodynamically related while nucleophiicity is kinetically decide. They're silent about each other. You need to practice and gather examples and an experience too :D