Question

For the compound having molecular formula $\mathrm{C_4H_9Br}$, write :
(a) the isomer which is most reactive towards $\mathrm{S_N1}$ displacement.
(b) the isomer which, on reacting with Na metal in the presence of dry ether, gives 2,5-Dimethylhexane.

Hint:

(a) most stable 3° carbocation = tert-butyl bromide; (b) Wurtz couples two isobutyl halves.

Answer 1

(i)
For naming a complex we list the ligands in alphabetical order, add the metal with its oxidation state in brackets, and finish with the counter ion. In $\mathrm{[PtCl_2(en)_2]SO_4}$ the ligands inside are two chlorides and two 'en' groups. Working out the metal's charge, the two 'en' are neutral and the two chlorides give $-2$, while the outside sulphate is $-2$, so the complex ion is $+2$ and platinum must be $+4$. Alphabetically chlorido comes before the ethanediamine, so the name is dichloridobis(ethane-1,2-diamine)platinum(IV) sulphate.

(ii)
Here the complex part is the negative ion $\mathrm{[CoF_4]^{2-}}$, with ammonium acting as the positive counter ion outside. When the complex ion is negative, the metal's name takes the '-ate' ending, so cobalt becomes cobaltate. Four fluorides give $-4$ and the whole ion is $-2$, so cobalt is $+2$. Putting the positive ammonium first, the name is ammonium tetrafluoridocobaltate(II).