Which of the following allotropes of sulphur exists as an `S_(6)` molecule having the chair conformation?

Options

A. `alpha` -sulphur
B. `beta` -sulphur
C. `gamma` -sulphur
D. `epsilon` -sulphur

Answer

4

Explanation

Sulphuric has more allotropic forms than any other element. These different forms arise partly from the extent to which `S` has polymerzed,and partly from the crystal structure adopted.
The two common crystallite forms are `alpha`or rhombic sulphur which is stable at room temperature and `beta` or monoclinic sulphur which is stable above `95.6^(@)`. These two forms change reverisbly with slow hearing or slow cooling.
Rhombic `S` occur naturally as large yellow crystals in volcanic area. A third modification known as `gamma-`monoclinic sulphur is nacreous (looks like mothr -of pearl). It can be made by chilling hot concentrated solutions of `S` in solvents such as `CS_(2)`, toluene or ethanol. All these forms contain puckered `S_(8)` rings with a crown conformation and differ only in the overall packing of the rings in the crystal. This affects their densities:
`{:(alpha-"rhombic," 2.069" g cm"^(-3)),(beta-"monoclinic," 1.94-2.01" g cm"^(-3)),(gamma-"monoclinic," 2.91" g cm"^(-3)):}`
The entalpy of transition from `alpha -S` to `beta-S` us small. Engel's Sulphur (`epsilon-`sulher) is unstable and contains `S_(6)` rings arranged in the chair conformation.