The structures of tetrasulphur tetranitride (a) and tetrathiazyl tetrafluoride (b) are given below. The statement that correctly describes the structures is :
Compound (b) satisfies Hückel rule and is more stable than (a)
The stem carries drawn structures with marked bond lengths; the four options are text and are reproduced in full above.
Compound (a) is S4N4, tetrasulphur tetranitride. It is not a planar aromatic ring at all but a cradle-shaped cage: the eight-membered S-N ring folds so that the two pairs of sulphur atoms bend towards each other, giving cross-ring S···S contacts of about 2.58 Å. The S-N distances are all similar (around 1.62-1.63 Å), showing delocalisation around the ring, but the folded geometry means the π system is not a planar Hückel system. S4N4 is also endothermic and shock sensitive — it detonates on grinding or heating.
Compound (b) is S4N4F4, tetrathiazyl tetrafluoride, obtained by fluorinating S4N4. Adding fluorine to each sulphur uses up the sulphur lone pairs and converts the cage into an eight-membered ring that adopts a puckered, crown-like conformation. The alternating bond lengths marked on the structure (about 1.54 Å and 1.66 Å) are the diagnostic point: unequal, alternating S-N distances mean localised single and double bonds rather than a delocalised system.
So neither compound is a genuine planar aromatic ring obeying the Hückel 4n+2 rule, and the bond-length alternation in (b) specifically rules out extensive delocalisation there.
Per the official final answer key the answer is option (C).
Similar Questions
The species that contain a vacant d x2 - y2 orbital is :
FeCl2 . 4H2O and FeCl3 . 6H2O can be distinguished by 57Fe Mössbauer spectroscopy. The INCORRECT statement from the following is :
The solutions of
(i) [Cr(OH2)6]3+ ions are pale blue-green, but the chromite ion
(ii) [CrO4]2- is an intense yellow due to :
The major product of the following reaction in :
In an axially symmetric field, the first NQR transition energy for I = $\frac{3}{2}$ is :
In the 19F NMR spectrum of ClF3, the number of signals and multiplicity at room temperature are (19F; I = \(\tfrac{1}{2}\)) :
Between NF3 and NH3 :
Identify (X) and (Y) in the following transformation :
The oxyacids of sulphur having direct S-S bonds are :
The point group of Cis - [PtCl2(NH3)2] is :
Important Questions from Structure of Atom
According to J.J. Thomson model of atom, positive charge is - Idenfity
- How many moles of He atoms are present in its 20 u mass ?
Which of the following electron transition in hydrogen atom will require largest amount of energy?
A species having 8 electrons in the third shell is very reactive while the other species having 8 electrons in the third shell is very inactive they are :
Which of the following is the general formula for saturated hydrocarbons?
