Question

& For each pair of species, predict which is the stronger base? NH (6) & Rank the following from most stable to least stable. CH ON CH₂CH CH₂CH2

Answer 1

5.

a)

Base can accept proton by sharing unshared pair of electrons.

NH₃ has one unshared electron pair whereas NH₄⁺ has no unshared electrons, hence NH₃ (B) can donate its unshared pair of electrons to a proton.So NH₃ (B) is strongest base.

b)

Phenoxide ion (A) has unshared pair of electrons ( formal charge is -1) so it can accept proton (H⁺) readily.

But Compound B is neutral, oxygen has already fulfilled its valency (2).

Hence phenoxide ion (A) is the strongest base .

c)

The anion a is more stabilized through resonance by the benzene ring than that of b. Hence the anion a can not donate easily its lone pair to a proton. Therefore anion b is strongest base.

6.

Stability of carbocation increases with increasing number of alpha hydrogens due to hyperconjugation.

H H CH (2) (1 CH3 H3 5 d-Hydrogens 2 d-Hy drogeng CH3 (3 CH2 H-C-H 8 -Hy drogeS CH3 (4) NO -HY dnogen I I

order of increasing stability is

4 < 2 < 1 < 3