Question

Which of the given statements is/are correct:

• A. The $C-Cl$ bond length in $C{H}_{3}C{H}_{2}Cl$ is $1.76\stackrel{\circ }{A}$ and $C{H}_2=CHCl$ is $1.69\stackrel{\circ }{A}$
• B. The $C=C$ bond length in $C{H}_2=C{H}_2$ is $1.34\stackrel{\circ }{A}$ and $C{H}_2=CHCl$ is $1.38\stackrel{\circ }{A}$
• C. The $C-C$ bond length in $C{H}_2=C{H}_2,C{H}_{3}C{H}_2-Cl$ and $C{H}_2=CHCl$ is $1.54\stackrel{\circ }{A}$
• D. The dipole moment of $C{H}_{3}C{H}_{2}Cl$ is greater than $C{H}_2=CHCl$

Answer 1

Answer: (A), (B), (D)

The correct options are
A The $C-Cl$ bond length in $C{H}_{3}C{H}_{2}Cl$ is $1.76\stackrel{\circ }{A}$ and $C{H}_2=CHCl$ is $1.69\stackrel{\circ }{A}$
B The $C=C$ bond length in $C{H}_2=C{H}_2$ is $1.34\stackrel{\circ }{A}$ and $C{H}_2=CHCl$ is $1.38\stackrel{\circ }{A}$
D The dipole moment of $C{H}_{3}C{H}_{2}Cl$ is greater than $C{H}_2=CHCl$

A)
In $C{H}_{3}C{H}_{2}Cl$, the carbon bonded with $Cl$ is $s{p}^3$ hybridised whereas in $C{H}_2=CHCl$, the carbon bonded with $Cl$ is $s{p}^2$ hybridised. As we know electronegativity is higher for $s{p}^2$ hybrisidisation than $s{p}^3$. Higher the electronegativity, greater will the tendency to pull the bond electrons towards itself which in turn leads to reduction of bond length. Hence, bond length is shorter in $C{H}_2=CHCl$.

(B) In $C{H}_2=C{H}_2$, there is no resonance whereas in $C{H}_2=CHCl$, there is a resonance and also lone pair of electron on $Cl$, which leads to slight single bond character in the $C-C$ bond, which in turns results in longer bond length.

(C) The $C-C$ bond length in $C{H}_2=C{H}_2,C{H}_{3}C{H}_2-Cl$ and $C{H}_2=CHCl$ is different in all three cases.


(D)

We know that dipole moment is calculated as $charge\times distance$, as discussed in (A) part bond length is larger in $C{H}_{3}C{H}_{2}Cl$ and also due to lesser electronegativity difference in $C-s{p}^2$ and $Cl$ as compared to $C-s{p}^3$ and $Cl$, charge separation is less in $C{H}_2=CHCl$. Hence, dipole moment is higher in $C{H}_{3}C{H}_{2}Cl$.