This question involves analyzing stable conformers of 1,2-dichloroethane (Cl-CH₂-CH₂-Cl) and identifying how many have a non-zero dipole moment. Conformers are different spatial arrangements of atoms resulting from rotation around single bonds.

Key Concepts:

1,2-dichloroethane can exist in several conformations due to rotation around the C-C bond. The main stable conformers are:

• Staggered (anti): Chlorine atoms are 180° apart.
• Staggered (gauche): Chlorine atoms are 60° apart.
• Eclipsed: Chlorine atoms are 0° or 120° apart (less stable due to steric strain).

Dipole Moment Consideration:

The dipole moment depends on the vector sum of individual bond dipoles (C-Cl bonds have significant dipole moments). For the dipole moment to be non-zero, the molecular geometry must not have perfect symmetry canceling out the dipoles.

Analysis of Stable Conformers:

Only staggered conformers are considered stable (minimized torsional strain):

• Anti conformer: The two C-Cl bond dipoles are anti-parallel and cancel each other perfectly. Net dipole moment = 0.
• Gauche conformer: The dipoles are at an angle (60°), so they do not cancel completely. Net dipole moment ≠ 0.

There are two equivalent gauche conformers (clockwise and anticlockwise rotation), but both have identical non-zero dipole moments. However, the question asks for the number of stable conformers with non-zero dipole moment, not the distinct values. Since both gauche conformers are stable and have non-zero dipole moment, the answer is 2.

Final Answer: 2 stable conformers (both gauche) have non-zero dipole moment.

Related Topics & Formulae

Conformational Isomerism: Study of different arrangements of atoms in a molecule that can be interconverted by rotation around single bonds.

Dipole Moment (μ): A measure of molecular polarity, calculated as the vector sum of individual bond dipoles. μ = q × d, where q is charge magnitude and d is distance.

Stability Order: Staggered (anti and gauche) > Eclipsed. Anti is most stable due to minimized steric and electronic repulsions, but gauche has higher energy due to chlorine clash.