Q.2-2-33 - Organic Chemistry (Mcmurry)

Question

Question:Phosgene, Cl₂C=O , has a smaller dipole moment than formaldehyde,H₂C=O  , even though it contains electronegative chlorine atoms in place of hydrogen. Explain.

Step-by-Step Solution

Answer

Answer

 

The dipole moment of fluoromethane is smaller than chloromethane because offluorine’s small size.

 

Step 1: Dipole moment

The dipole moment, $\mathit{\mu }$,tells the net molecular polarity at both ends of the molecular dipole.  The dipole moment depends on the charge transfer between the atoms. If there is symmetry, then the molecules have no net dipole moment.

The direction of the dipole moment is indicated by an arrow toward a more electronegative atom.

Step 2: Factors affecting dipole moment

The dipole moment is defined as the magnitude of the chargeat both ends of the molecular dipole multiplied by the distance r between the costs, which is the bond length. 

$\mu =Q\times r$ 

From the formula, both electronegativity of atoms and the size of a molecule affect dipole moment. More the size more will be the dipole moment.

Step 3: Comparison of the structure of phosgene and formaldehyde

Dipole moment depends on both electronegativities of atoms and the size of the molecule.

 $\mu =Q\times r$

Here, fluorine is more electronegative than chlorine but is much smaller, while chlorine is less electronegative than fluorine but much more prominent in size.

The larger size of chlorine increases the distance between carbon and a chlorine atom, compensating for the higher electronegativity of fluorine even though it is more electronegative.