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Q. The Lewis structure of allene is

Question

Which of the following statements correctly gives answers for all 3 parts:

(a) Is the molecule planar?

(b) Does 1, 3 - dichloro propadiene show geometrical isomerism?

(c) Is the molecule 1, 3 - dichloro propadiene polar?

NTA AbhyasNTA Abhyas 2020Chemical Bonding and Molecular Structure

Solution:

Hybridization of central carbon is sp and two of its unhybridized p -orbitals are involved in π - bonding. Also p - orbitals at an atom are orthogonal (at 90ο angle), the two π - bonds at central carbon are also orthogonal. Let these p - orbitals, involved in π - bonding, at central carbon be py and pz , then

Solution

Hybridization at the terminal carbons are both sp2 . The two p - orbitals involved in sp2 hybridization are px and py at left terminal and px and pz at right terminals. Therefore, the three sp2 hybrid orbitals at left terminal carbon are in xy plane, while the same at right terminal carbon are in xz

plane. As a result, the two triangular planes at terminals are at right angles as shown below:

Solution

The two H - C - H planes at terminals are perpendicular to each other. ( π - bonds are also perpendicular to each other.)

Hence, (a) Molecule is non - planar. (b) It doesn't show geometrical isomerism because two H and chlorine are in different planes. (c) polar.