Q10.71CP - Chemistry: Molecular Nature Of Matter And Change

Question

Chloral, ${\mathbf{Cl}}_3\mathbf{CCH}\mathbf{=}\mathbf{O}$ , reacts with water to form the sedative and hypnotic agent chloral hydrate,  ${\mathbf{Cl}}_3\mathbf{CCH}\mathbf{(}\mathbf{OH}{\mathbf{)}}_2$  . Draw Lewis structures for these substances, and describe the change in molecular shape, if any, that occurs around each of the carbon atoms during the reaction.

 

Step-by-Step Solution

Answer

The Lewis structures for the given substances.

The change in molecular shape:

Here, the ${\mathbf{sp}}^2$  carbon (in chloral) changes to   ${\mathbf{sp}}^3$ carbon (in chloral hydrate) and the bond angle changes from  $\mathbf{120}\mathbf{°}$ to  $\mathbf{109}\mathbf{.}\mathbf{5}\mathbf{°}$.

 

Step 1: Structure of chloral.

In chloral, one carbon is attached with three chlorine atoms and one carbon atom. hence the hybridization of this carbon is ${\mathbf{sp}}^3$  and the geometry will be tetrahedral. Another carbon atom is bonded with one hydrogen and one carbon atom with a single bond and with one oxygen atom with a double bond. Hence the hybridization of this carbon is  ${\mathbf{sp}}^2$ and the geometry will be trigonal planar. 

 

The bond angle is   $\mathbf{120}\mathbf{°}$.

 

Step 2: Structure of chloral hydrate

In chlorate hydrate one carbon is attached with three chlorine atoms and one carbon atom. Hence the hybridization of this carbon is ${\mathbf{sp}}^3$  and the geometry will be tetrahedral. Other carbon atom is bonded with two -OH group, one carbon atom, and one hydrogen atom. Hence the hybridization is  ${\mathbf{sp}}^2$  and the geometry will be tetrahedral.

 

The bond angle is   $\mathbf{109}\mathbf{.}\mathbf{5}\mathbf{°}$.

Step 3: Deviations or the change in molecular shape.

The ${\mathbf{sp}}^2$  carbon of chloral changes to  ${\mathbf{sp}}^{\mathbf{3}}$ carbon in chloral hydrate and the bond angle changes from $\mathbf{120}\mathbf{°}$  to $\mathbf{109}\mathbf{.}\mathbf{5}\mathbf{°}$ .

So, the geometry changes form trigonal planar to tetrahedral.