Find the odd one out.-OH,-OR-,NH2,-COOH,-NHCOR

The atoms or substituent groups, which represent +R or -R electron displacement effects are as follows ;+R-effect: - halogen, -OH,-OR,-OCOR,-NH2 -NHR,-NR2,-NHCOR-R-effect; -COOH,-CHO,>C==O,-CN,-NO2Thus, -COOH is a - R effect showing group while other show +R effect.