Question

Hexane gives two monochloro alkanes on chlorination

Answer 1

$\huge{He¥ MaTe!!!}$

☆☞ Here is ur answer ☜☆

✔✔ Yes, generally alkenes have higher melting and boiling point than alkanes.

✔✔ The rule of thumb is “Higher the intermolecular forces (the force by which molecules attract molecules), higher is the melting and boiling point”.

✔✔ Alkanes are apolar i.e their molecules have negligible dipole moment because of almost equal electronegativity of C and H atoms. The only attractive force between alkane molecules is induced dipole-induced dipole weak Van der Wall’s forces. That’s why their melting and boiling point is very low.

✔✔ Alkenes have little dipole moment in them. Their intermolecular forces is dipole-induced dipole-dipole Van der Wall’s forces. However these dipole moments are low, so the melting and boiling points of alkenes are only little higher than alkanes.

✔✔ Then the question rises why alkenes possess little dipole moments as they have also C and H only? The answer is the π bond of alkenes are loosely held and move more freely than σ bond. The alkyl group attached to carbon containing double bond pushes its electron during momentarily absence of the π electron from the vicinity of C atom containing double bond. Hence the alkyl group shows +I (pushing Inductive effect) when attached to double bonded C atom. This gives a little dipole moment to the alkene molecule.

As we can see,

Dipole moment of Propane is 0.08 D

Dipole moment of Propene is 0.36 D

and,

Dipole moment of cis But-2–ene is 0.33 D

Dipole moment of trans But-2-ene is negligible.

HOPE IT HELPS!

Answer 2

Yes, generally alkenes have higher melting and boiling point than alkanes.