Final answer:
The strongest electron-attracting species among the given options is -CN (cyano group), mainly due to the high electronegativity of nitrogen and the presence of a triple bond in the CN group.
Step-by-step explanation:
The question seeks to identify which of the given species is the strongest electron-attracting group. To answer this, it's important to understand that molecules or ions attract electrons based on their ability to stabilize negative charges, typically through electronegativity or resonance stabilization.
Looking at the options provided, we have -CN, -NH2, -NHR, and -NHOR. Among these, -CN (cyano group) is known to be a very strong electron-attracting group. This is due to the triple bond between carbon and nitrogen, where nitrogen is highly electronegative. Moreover, the cyano group is present at the end of the spectrochemical series, indicating that it has a high ligand field strength and, consequently, a strong ability to attract electrons.