Question

Which of the following statements are correct

• A. $\overset{\ominus}{O}H$ is weaker nucleophile than $H_2O$
• 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 $\overset{\ominus}{ OH }$ is a stronger nucleohile than $H _2 O$. Statement (a) is wrong
b. RSH is a stronger acid than ROH (except $MeOH$ ). $RS ^{\ominus}$ is a weaker base and weaker nucleophile (stronger the acid, weaker is its conjugate base)
Therefore $RS ^{\ominus}$ should be a weaker uncleophilethan $RO ^{\ominus}$. But in polar protic solvent such as ethanol, RSH is less solvated than ROH (due to H-bonding)
Therefore, $RS ^{\ominus}$ is a stronger uncleophile than $RO ^{\ominus}$ statement (b) is correct
c. $H _2 \ddot{N} -\ddot{ O H}$ is a stronger base and hence a stronger nucleophile than $NH _3$. 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