Nucleophiles and electrophiles are reaction intermediates having electron rich and electron deficient centres respectively. Hence, they tend to attack electron deficient and electron rich centres respectively. Classify the following species as electrophiles and nucleophiles.

Option (i) it can be considered into two groups the methoxy (CH₃O ─) group or the hydroxyl-methyl group (HO ─ CH₂^-). As the charge is mentioned on oxygen the given reagent is a methoxy anion. As the reagent is rich in electron it would tend to donate or share those electrons by acting as nucleophile.

Option (ii) carbonyl carbon is highly electron deficient as it is bonded with two oxygen atom and thus the central atom acts as a site with δ+ charge. This charge implies that carbonyl group acts as an electrophile with carbon as an attacking site.

Even the movement of negative charge seems to imply the molecule being a nucleophile, the concerned site of activity is the central carbon atom and not the negative charge on oxygen atoms which is in itself difficult for attack due to resonance.

Option (iii) chloride radical is electron rich as it contains 7 electrons in its outermost shell and needs only one electron to complete its octate, so it needs an electron implying it to be an electrophile.

*Important Note: free radicals can act as both as an electrophile or nucleophile depending on the attacking site which in turn depend on various factors such as stearic hindrance, electron repulsion, thermodynamic stability, stability of the radical itself, and so on.

So if we consider a relatively linear molecule for attack, Cl radical will act as an electrophile under standard conditions.

Option (iv)

It seems the lone pair is a willing donor of electrons but the outer octate for carbon is complete and has only six electrons with an empty sp³ hybrid orbital giving a planar structure to the molecule, this planar structure enhances its attacking probability. Deficiency in electrons shows it will act as an electrophile and attack an electron rich site of the substrate.

Option (v)

Tertiary carbocation is greatly stabilised by the positive inductive effect form methyl groups and the hyperconjugating structure from 9 α- carbon atoms. This increase in stability and its positive charge implies that it will act as an electrophile as it is an electron deficient species.

Option (vi) Br^- is a nucleophile, due its complete octate and big atomic size, it tends to decrease its stability due to less electronegativity as compared to F and Cl. So the tendency to give electron is more than to receive, thus Br^- acts as an nucleophile

Option (vii)

Undernormalcircumstances oxygen atom in alcohol act as a nucleophile under the influence of strong electrophile. An example is shown above example.

Option (viii) amides are bases that donate electrons and act as a nucleophile.

The lone pair on nitrogen is the donor atom, this tendency to donate the electorns is further emphasized by the alkyl groups if attached to it due to positive inductive effect.