Question

Which of the following has the highest boiling point?
A.1-Chloropentane
B.2-chloropentane
C.3-chloropentane
D.All have equal boiling point

Answer 1

Hint: To find out the highest boiling point among different organic compounds we should know the boiling points shows the strength of forces between molecules. The more they stick together, the more energy it will require to transform liquid into vapours.

Complete answer:
We should first understand the concept of boiling point. We should know about important trends that we should consider in determining the relation between boiling points of different compounds.
We should know about three important trends:
1.We should know about the relative strength of the four intermolecular forces: Ionic > Hydrogen bonding > dipole > Van der Waals dispersion forces. The influence of each of these attractive forces will depend on the functional groups present.
2.Boiling points increase as the number of carbons is increased.
3.Branching decreases boiling point.
In determining the boiling point of the above options, we should note that all the options are derivative of chloro pentane. In each option, chlorine is present at a different position in pentane.
Molecules with a given functional group, boiling point increases with molecular weight. We should know that the key force that is acting here are Van der Waals dispersion forces, which are proportional to surface area. So as we increase the length of the chain, there is also an increase in the surface area, which means that it increases the ability of individual molecules to attract each other.
2−chloropentane is branched. So, its surface area is lower than that of 1−chloropentane. We know from the above discussion that surface area decreases the ability of molecules to interact through Van der waal forces. So, it will decrease the boiling point also.
So, 1−chloro−pentane has the highest boiling point.
So, from the above discussion we can say that 1−chloro−pentane has the highest boiling point. So, from this we can say that option A is correct and it has high boiling point.

Note: We should know that cycloalkanes have boiling points that are approximately 20 K higher than the corresponding straight chain alkane.
We should note that the boiling point of a liquid varies with the surrounding atmospheric pressure. A liquid at a higher pressure has a higher boiling point than when that liquid is at lower atmospheric pressure.
We should know that the normal boiling point of a compound is an indicator of the volatility of that compound. The higher the boiling point, the less volatile is the compound. Conversely, the lower the boiling point, the more highly volatile is the compound. At a given temperature, if a compound’s normal boiling point is lower, then that compound will generally exist as a gas at atmospheric pressure. If the boiling point of the compound is higher, it then exists as a liquid or a solid.