Grignard reagents (and their relatives, organolithium reagents) are extremely important nucleophiles.
Let’s look at why they’re nucleophiles first. (Remember: nucleophilicity = nucleus-loving, i.e. seeks out positive charge).
Compare the electronegativities of Mg and C. Or Li for that matter.
See how the partial negative charge is on the carbon? That means it’s going to seek out positive charge.
Grignard reagents will react with many electrophiles (positively charged species) which you have already met, such as ketones (or aldehydes), epoxides, or acids. Here are some examples.
Note: for the first reaction, it’s OK to gnore the “ether”. That’s just the solvent here. It makes no key difference to the reaction.
Tomorrow: All about this weird thing we call “conjugation”
Thanks for reading! James