MCQ
The following bimolecular elimination reaction $(E_2)$ is carried out with different halogen leaving groups. The per cent yield of the two products ($2$ -hexene and $1$-hexene) for each leaving group is listed below.
| Leaving group | Conj. Acid $pK_a$ | $\%$ -yield of $2$-hexene | $\%$ -yield of $1$ -hexene |
| $X = I$ | $- 10$ | $81\%$ | $19\%$ |
| $X = Br$ | $-9$ | $72\%$ | $28\%$ |
| $X = Cl$ | $-7$ | $67\%$ | $33\%$ |
| $X = F$ | $3.2$ | $30\%$ | $70\%$ |
Which of the following statement is (are) true concerning this series of $E_2$ reactions ?
- ABased on the $pK_a$ 's of the conjugate acid, $I^-$ is the best leaving group and $F^-$ is the poorest leaving group
- BWhen $I^-, Br^-$ and $Cl^-$ are used as leaving groups, Zaitsev's rule is followed
- C$F^-$ is the strongest base (and therefore the poorest leaving group) and the transition state for reaction with fluoride as the leaving group has the least double bond character
- ✓$a, b, c$ are true