It helps me to think of EAS (electrophilic aromatic substitution) groups like this. The charges listed are not really there-the carbons are not actually fully charged, the charge labels are there to illustrate areas of low electron density (+) and areas of high electron density (-). Recall that nucleophiles go for the (+) areas. This is why groups direct. Electron donating groups=EDG Electron withdrawing groups=EWG Halides are technically EWG, but they act as ortho/para directors anyways.
N--Acetyl Cysteine (NAC) is an amino acid that is commonly used as an antioxidant and as a mucolytic agent. Antioxidants are a group of substances that are capable of reducing oxidation in the body. Antioxidants are able to do this by donating an electron to free radicals (and thereby neutralizing the free radical). This process is on-going and never ending....for flushing out heavy metals