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Consider the following two statements about the dipole moments of dichlorobenzene isomers: Statement 1: The dipole moment of para-dichlorobenzene is zero because of its symmetrical structure. Statement 2: ortho-dichlorobenzene has a larger dipole moment than meta-dichlorobenzene because of the smaller angle between the two C-Cl bond dipoles in the ortho isomer. Which of the following is correct?

1. (A) Both Statement 1 and Statement 2 are correct
2. (B) Statement 1 is correct but Statement 2 is incorrect
3. (C) Statement 1 is incorrect but Statement 2 is correct
4. (D) Both Statement 1 and Statement 2 are incorrect

Correct answer: (A) Both Statement 1 and Statement 2 are correct

Solution

Statement 1: In para-DCB the two C-Cl bonds point in exactly opposite directions (180 deg apart), so the vector sum of their dipole moments is zero. Statement 1 is correct. Statement 2: The resultant of two equal vectors of magnitude mu at angle theta is 2*mu*cos(theta/2). For ortho (theta ≈ 60 deg): 2*mu*cos 30 ≈ 1.73*mu. For meta (theta ≈ 120 deg): 2*mu*cos 60 = mu. So ortho > meta, and the reason (smaller angle between bond dipoles) is correct. Both statements are correct.

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