Organic Chemistry Basics - Result Question 169
####20. Which of the following will have least hindered rotation about carbon-carbon bond?
(a) Ethane
(b) Ethylene
(c) Acetylene
(d) Hexachloroethane
(1987, 1M)
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Answer:
Correct Answer: 20. (b)
Solution:
- Allene is the name given to propdiene, $H _2 C=C=CH _2$
Hybridisation of an atom is determined by determining the number of hybrid orbitals at that atom which is equal to the number of sigma $(\sigma)$ bonds plus number of lone pairs at the concerned atom.
$\operatorname{Pi}(\pi)$ bonds are not formed by hybrid orbitals, therefore, not counted for hybridisation.
Here, the terminal carbons have only three sigma bonds associated with them, therefore, hybridisation of terminal carbons is $s p^{3}$. The central carbon has only two sigma bonds associated, hence hybridisation at central carbon is $s p$.
