For each alkene, indicate the direction of the dipole moment. For each pair, determine which compound has the larger dipole moment.
a. cis-1,2-difluoroethene or trans-1,2-difluoroethene

Verified step by step guidance

1. Identify the molecular structure of cis-1,2-difluoroethene and trans-1,2-difluoroethene. In the cis isomer, both fluorine atoms are on the same side of the double bond, while in the trans isomer, they are on opposite sides.
2. Understand that the dipole moment is a vector quantity that depends on the difference in electronegativity between atoms and the geometry of the molecule. Fluorine is more electronegative than carbon, creating a dipole in the C-F bond.
3. For cis-1,2-difluoroethene, the dipole moments of the two C-F bonds add up because they are in the same direction, resulting in a net dipole moment pointing from the hydrogen side towards the fluorine side.
4. For trans-1,2-difluoroethene, the dipole moments of the two C-F bonds cancel each other out because they are in opposite directions, resulting in a net dipole moment of zero.
5. Compare the net dipole moments: cis-1,2-difluoroethene has a larger dipole moment than trans-1,2-difluoroethene because the dipoles in the trans isomer cancel out, while in the cis isomer, they reinforce each other.

Key Concepts

Dipole Moment

The dipole moment is a measure of the separation of positive and negative charges in a molecule. It is a vector quantity, having both magnitude and direction, and is influenced by the electronegativity of atoms and the geometry of the molecule. In alkenes, the dipole moment is determined by the arrangement of substituents around the double bond.

Cis-Trans Isomerism

Cis-trans isomerism, also known as geometric isomerism, occurs in alkenes due to restricted rotation around the double bond. In cis isomers, similar groups are on the same side of the double bond, while in trans isomers, they are on opposite sides. This spatial arrangement affects the dipole moment, as cis isomers often have a higher dipole moment due to the additive effect of the dipoles.

Electronegativity

Electronegativity is the tendency of an atom to attract electrons towards itself in a chemical bond. In molecules like difluoroethene, fluorine's high electronegativity creates a polar bond with carbon, contributing to the molecule's overall dipole moment. The difference in electronegativity between bonded atoms is a key factor in determining the direction and magnitude of the dipole moment.