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Molecule which is NOT capable to show optical isomerism is:

Molecule which is NOT capable to show optical isomerism is: Correct Answer <img alt="F1 Utkarsh Shraddha 28.11.2020 D13" src="//storage.googleapis.com/tb-img/production/20/12/F1_Utkarsh_Shraddha_28.11.2020_D13.png" style="width: 163px; height: 92px;">

Concept:

Super impossibility of images-

  • Two images are said to be superimposable on each other if their corresponding parts coincide when one is placed upon the other. 
  • If they do not coincide, then they are called non-superimposable on its mirror image.

 

[ alt="F1 Utkarsha 30.12.20 Pallavi D8" src="//storage.googleapis.com/tb-img/production/21/01/F1_Utkarsha_30.12.20_Pallavi_D8.png" style="width: 330px; height: 397px;">

Optical isomerism:

  • When two isomers rotate plane polarised light in different directions, then they are known as optical isomers.
  • The phenomenon is known as optical isomerism.

​​Criteria to show optical isomerism-

  • Absence of center of Symmetry- when a line is drawn from the centre of a molecule towards the corner of each atom, it should not encounter similar atoms.
  • Absence of plane of symmetry- A real or imaginary plane, vertical or horizontal when passed through a molecule, bisects it so that the one half of the molecule should not be the mirror image of the other half.
  • The presence of Chiral centre-An object or molecule which has no plane of symmetry and is not superimposable on its mirror image is said to be chiral or dissymmetric.

​Explanation:

Let us examine the given molecules for chiral centres

[ alt="F1 Utkarsha 30.12.20 Pallavi D9" src="//storage.googleapis.com/tb-img/production/21/01/F1_Utkarsha_30.12.20_Pallavi_D9.png" style="width: 230px; height: 148px;">

  • Alkenes are planar molecules. 
  • They have a horizontal plane (the plane of the paper) bisecting it in two similar halves (up and below).

Hence is not chiral and will not show optical isomerism.

[ alt="F1 Utkarsha 30.12.20 Pallavi D11" src="//storage.googleapis.com/tb-img/production/21/01/F1_Utkarsha_30.12.20_Pallavi_D11.png" style="width: 321px; height: 209px;">

[ alt="F1 Puja.J 28-01-21 Savita D4" src="//storage.googleapis.com/tb-img/production/21/01/F1_Puja.J_28-01-21_Savita_D4.png" style="width: 166px; height: 92px;">

  • The molecule given above is an allene molecule.
  • The Central carbon atom is sp hybridised.
  • The two pi bonds lie perpendicular to each other and thus there exists no element of symmetry.

The molecule thus becomes optically active and is capable of showing optical isomerism.

[ alt="F1 Puja.J 28-01-21 Savita D3" src="//storage.googleapis.com/tb-img/production/21/01/F1_Puja.J_28-01-21_Savita_D3.png" style="width: 120px; height: 120px;">

  • The molecule has four different groups tetrahedrally attached to it. 
  • No symmetrical elements are present and also the carbon centre is chiral.
  • The mirror images are also not superimposable on each other.

Hence, it will show optical isomerism.

Thus, the molecule which is NOT capable to show optical isomerism is [ alt="F1 Utkarsh Shraddha 28.11.2020 D13" src="//storage.googleapis.com/tb-img/production/20/12/F1_Utkarsh_Shraddha_28.11.2020_D13.png" style="width: 163px; height: 92px;">.

 

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