Question

For a given alkyl group, the boiling points of alkyl halides follow the order:
A. \[{\rm{RI}}\,\,{\rm{ > }}\,\,{\rm{RBr}}\,\,{\rm{ > }}\,\,{\rm{RCl}}\]
B. \[{\rm{RCl}}\,\,{\rm{ > }}\,\,{\rm{RBr}}\,\,{\rm{ > }}\,\,{\rm{RI}}\]
C. \[{\rm{RI}}\,\,{\rm{ > }}\,\,{\rm{RCl}}\,\,{\rm{ > }}\,\,{\rm{RBr}}\]
D. \[{\rm{RBr}}\,\,{\rm{ > }}\,\,{\rm{RI}}\,\,{\rm{ > }}\,\,{\rm{RCl}}\]

Answer 1

Hint: Alkyl halides are the derivatives of alkanes in which a hydrogen atom is replaced by a halogen atom \[{\rm{(F,}}\,\,{\rm{Cl,}}\,\,{\rm{Br,}}\,\,{\rm{or}}\,\,{\rm{I)}}\]. They are called alkyl halides because their molecules are made of an alkyl group attached to a halogen atom. They are represented by the formula \[{\rm{R}} - {\rm{X}}\], where \[{\rm{R}}\]is an alkyl group and \[{\rm{X}}\]is a halogen atom.

Complete Step by Step Solution:
In general, it can be said that the compounds containing a halogen atom bonded to a saturated carbon are referred to as alkyl halides. These can be divided into three classes according to the halogen attached to a primary, secondary or tertiary carbon.

Alkyl halides do not occur free in nature and yet they are amongst the most useful of the aliphatic compounds. They are frequently used for introducing alkyl groups into other molecules and thus form the basis for the synthesis of innumerable organic compounds. Alkyl halides are excellent solvents for many organic materials and are much used in industry.

The boiling points of alkyl halides are much higher than those of alkanes with the same carbon skeleton. In general, the boiling points rise with an increase in molecular weight and decrease with the branching of the alkyl group. For the various types of alkyl halides, the boiling points are in the order \[{\rm{RI}}\,\,{\rm{ > }}\,\,{\rm{RBr}}\,\,{\rm{ > }}\,\,{\rm{RCl}}\].
Therefore, option A is correct.

Note: The properties of alkyl halides essentially depend upon the nature and strength of the carbon-halogen bond \[{\rm{(C}} - {\rm{X)}}\]. Alkyl halides are generally quite toxic substances and need to be handled with care. Although they are slightly polar, alkyl halides are insoluble in water because of their inability to form hydrogen bonds. They are readily soluble in organic solvents.