If one of the hydrogens in the alkyl side chain of ethanoic acid is replaced with an atom of Chlorine, the acid has a larger Ka value. My book says this is since the Cl "borrows" electron density from the Carbon it is connected to. And, in this example, this carbon borrows some electron density from the Carbon in the acid group, and thus the oxygens of the acid have less charge density. The bold part is what I don't get.
The C to which this 1 chlorine is attached gets a bit electron deficient but not as much deficient as the C in the acid group (since this has two oxygen atoms attached). So how can it borrow density away from the C in the acid group? In my mind, to borrow some charge density you have to be more electronegative than what you're attached to, and the more deficient carbon should have a greater pull.
What am I missing in this?