Question

2. Circle the better leaving group in each pair. SH : ОН Нон HO O Br CH3 3. Circle the stronger nucleophile in each pair. НОн ОН SH HO N H H CH3 .N H ОН OH

Answer 1

2.The leaving group is the functional group that is eliminated with electrons of the sigma bond in a reaction.

Better the leaving group faster is the sN1 and sN2 reactions.

The relative ability of leaving group Y in R-Y bond is influenced by the strength of the R-Y bond and the stability of Y^- .

Good leaving groups are weak bases or the conjuagte bases of strong acids.

Between Br^- and Cl^-, bromide Br^- is the better leaving group due to its larger size and hence, Br^- is stabilised more.

Between OH^- and H₂O , WATER H₂O is the better leaving group. Because water is a weak conjugate base of strong acid, hydronium ion. As OH^- is a strong base, therefore it is a bad leaving group.

Between acetate CH₃COO^- and CH₃SO₃^- (MESYLATE ION) , mesylate ion is the better leaving group.

The reason is the ion is more stabilised by resonance.

Between SH^- and OH^- , SH^- is the better leaving group.

Since sulfur is larger than oxygen and hence, the negative charge on SH^- is more stabilised.

3. A nucleophile is a species which can donate a pair of electrons to an electrophile. It is a Lewis base.

Between OH^- AND H₂O , OH^- ion is the better nucleophile due to its more electron density on OXYGEN.

Between SH^- AND OH^- (hydroxide ion) , SH^- is the better nucleophile. Since oxygen is more electronegative than sulphur ,so its ability to donate electrons decreases.Hence, SH^- is more nucleophilic in nature.

Between acetic acid and ethanol, ethanol is the better nucleophile.

Due to existence of resonance in acetic acid,makes the electrons on oxygen less available for donation. Hence, ethanol is the better nucleophile between ethanol and acetic acid.

Between methyl amine CH₃NH₂ and the other given amine, steric hinderence is more in the second amine.Due to this its donation of electrons (nucleophilicity)is poor. Due to this, it is a poor nucleophile than methyl amine.Hence, methyl amine is the better nucleophile.