Question

Which of the following statements are correct

• A. $\stackrel{\ominus }{O}H$ is weaker nucleophile than $H_{2}O$
• B. $R-\ddot{\underset{..}{S}}H$ is a stronger nucleophile than $R-\ddot{\underset{..}{O}}H$ in polar protic solvent such as ethanol
• C. $\ddot{N}{H}_3$ is a weaker nucleophile than $H_2\ddot{N}-\ddot{\underset{..}{O}}H$
• D. is a stronger nucleophile than ${\left(C_2{H}_5\right)}_3\ddot{N}$ (II)

Answer 1

Answer: (B), (C), (D)

a. Stronger the base stronger is the nucleophile therefore $\stackrel{\ominus }{\mathrm{OH}}$ is a stronger nucleohile than $H_{2}O$. Statement (a) is wrong
b. RSH is a stronger acid than ROH (except $MeOH$ ). $R{S}^{\ominus }$ is a weaker base and weaker nucleophile (stronger the acid, weaker is its conjugate base)
Therefore $R{S}^{\ominus }$ should be a weaker uncleophilethan $R{O}^{\ominus }$. But in polar protic solvent such as ethanol, RSH is less solvated than ROH (due to H-bonding)
Therefore, $R{S}^{\ominus }$ is a stronger uncleophile than $R{O}^{\ominus }$ statement (b) is correct
c. $H_2\ddot{N}-\ddot{OH}$ is a stronger base and hence a stronger nucleophile than $N{H}_3$. Statement (c) is correct
d. In (I), all $\beta -C$ are tied up with a $C$ atom, while in (II), the substituents bonded to $N$ atom are almost free to rotate and causesteric hindrance during approach of LP $\overline{\bar{e}}$ 's to the attacking site
In other words, LP ${\bar{e}}^{\prime }$ s on $N$ in (I) are easily available but in (II) they are stericallyhindered
Thus, (I) is a stronger base and hence a stronger nucleophile than (II)
Statement (d) is correct