Question

Which of the following statement is correct? (1) Cis alkenes arc polar and hence have more boiling points than trans isomers but trans isomers are non-polar with low boiling points (2) Trans isomers are symmetrical and hencc pack more closcly in crystal lattice causing more melting points than cis isomers (3) \Lambdalkencs arc insoluble in water but soluble in organic solvents (4) \Lambdall are correct

Short answer

Statement (4) is correct.

Step-by-step solution

Analyze statement (1)

Cis alkenes have dipole moments causing them to be polar, while trans alkenes typically have no net dipole moment, making them non-polar. This results in cis alkenes often having higher boiling points than trans alkenes due to stronger intermolecular forces.

Analyze statement (2)

Trans isomers are more symmetrical and can pack closer together in a crystal lattice, resulting in stronger intermolecular forces and typically higher melting points compared to cis isomers.

Analyze statement (3)

Alkenes, including both cis and trans isomers, are non-polar molecules, making them generally insoluble in water (a polar solvent), but soluble in organic solvents (non-polar solvents).

Analyze statement (4)

If statements (1), (2), and (3) are all accurate descriptions, then statement (4) that suggests all previous statements are correct will also be true.

Conclusion

Since statements (1), (2), and (3) are all analytically correct, statement (4) is the most accurate assessment.

Key concepts

Cis-Trans Isomerism

Cis-Trans isomerism is a type of stereoisomerism where compounds have the same structural formula but differ in the spatial orientation of atoms. This kind of isomerism occurs in alkenes due to the presence of a double bond, which restricts the rotation of the molecule.
Cis isomers have similar groups on the same side of the double bond, whereas trans isomers have similar groups on opposite sides.
Cis and trans isomers often have different physical properties due to their shapes and polarity. Cis isomers tend to be more polar than trans isomers, which can affect their boiling and melting points as well as their solubility in different solvents.

Intermolecular Forces

Intermolecular forces are the forces of attraction between molecules. These forces are crucial in determining the physical properties of substances, such as boiling and melting points.
There are different types of intermolecular forces:

• **London dispersion forces**: Weak forces due to temporary dipoles in molecules.
• **Dipole-dipole interactions**: Occur between polar molecules.
• **Hydrogen bonds**: Strong type of dipole-dipole interaction, involving hydrogen and highly electronegative atoms like oxygen, nitrogen, or fluorine.

Cis alkenes are more polar because of the grouping of similar substituents on the same side, resulting in stronger dipole-dipole interactions compared to trans alkenes, which are less polar. Thus, cis isomers generally have higher boiling points due to these stronger intermolecular forces.

Solubility

Solubility is the ability of a solute to dissolve in a given solvent. It depends on the intermolecular forces between the solute and the solvent.
Alkenes, including both cis and trans isomers, are non-polar molecules. Because polar water molecules cannot form strong interactions with non-polar alkenes, alkenes are generally insoluble in water.
However, alkenes are soluble in organic solvents such as hexane or benzene, which are also non-polar. The rule of thumb 'like dissolves like' explains this phenomenon; substances tend to dissolve well in solvents that have similar polarity.

Melting and Boiling Points

Melting point and boiling point are physical properties that give insights into the strength of the intermolecular forces within a substance.
**Melting point** is the temperature at which a solid turns into a liquid.
**Boiling point** is the temperature at which a liquid turns into a vapor.
Trans isomers usually have higher melting points than cis isomers due to their symmetrical shape, which allows them to pack more closely in a solid state. This close packing increases the strength of the intermolecular forces.
Cis isomers often have higher boiling points because they are more polar, leading to stronger dipole-dipole interactions that require more energy to break during the transition from liquid to gas.