Q.Arrange the following in increasing order of boiling points.
a. 1-Bromopropane
b. 2-Bromopropane
c. 1-Bromobutane
d. 1-Bromo-2-methylpropane

The physical properties of alkyl and aryl halides follow from the polarity and size of the C-X bond. Because every halogen is more electronegative than carbon, C-X is a polar covalent bond (C-delta+, X-delta-), making alkyl halides moderately polar; going down the halogen group, C-X bond length increases and bond strength (bond enthalpy) decreases, because a larger halogen's more diffuse p-orbital overlaps less effectively with carbon (for the methyl halides: C-F 139 pm/452 kJ/mol down to C-I 214 pm/234 kJ/mol). Boiling points of alkyl halides are considerably higher than the parent alkane's, and within a series they rise with the atomic mass of the halogen (RI>RBr>RCl>RF, since van der Waals attraction grows with the halogen's size/mass), rise with increasing carbon-chain length for a given halogen (more surface area, stronger van der Waals attraction), and fall with increased branching among isomers (a more compact, sphere-like molecule has less surface area and hence weaker van der Waals attraction than its straight-chain isomer). Despite being moderately polar, alkyl halides …