Consider the following set of chlorinated compounds: 1. 2. 3. -dichlorobenzene 4. -trichlorobenzene — Haloalkanes and Haloarenes Chemistry Question
Question
Consider the following set of chlorinated compounds: 1. $CCl_4$ 2. $CHCl_3$ 3. $1,4$ -dichlorobenzene 4. $1,3,5$ -trichlorobenzene 5. $1,2,3,4,5,6$ -hexachlorobenzene 6. trans- $1,2$ -dichloroethene 7. cis- $1,2$ -dichloroethene How many of these compounds possess a net dipole moment exactly equal to zero?
💡 Solution & Explanation
To have a net zero dipole moment, the molecule must possess highly symmetrical geometry where all individual bond dipole vectors perfectly cancel. 1. $CCl_4$: Tetrahedral and symmetrical $\rightarrow$ Zero. 2. $CHCl_3$: Tetrahedral but asymmetrical ($C-H$ vs $C-Cl$) $\rightarrow$ Non-zero. 3. $1,4$ -dichlorobenzene ($p$ -dichlorobenzene): Symmetrical, vectors at $180^\circ$ $\rightarrow$ Zero. 4. $1,3,5$ -trichlorobenzene: Symmetrical trigonal planar arrangement, vectors at $120^\circ$ cancel out $\rightarrow$ Zero. 5. Hexachlorobenzene: Fully symmetrical regular hexagon $\rightarrow$ Zero. 6. trans- $1,2$ -dichloroethene: Inversion center, $C-Cl$ vectors cancel $\rightarrow$ Zero. 7. cis- $1,2$ -dichloroethene: Both $C-Cl$ vectors point in the same general direction $\rightarrow$ Non-zero. Total number of compounds with zero dipole moment = 5.