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Arrange the followig compounds in increasing order of boiling points: (a) pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, methanol. (b) pentan-1-ol, n-butane, pentanal, ethoxyethane. |
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Answer» Solution :(a) Boiling points increase REGULARLY as the molecular mass increases due to the corresponding increase in their van der waals forces of ATTRACTION. Thus, boiling points increase in the order: METHANOL, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol. Among ISOMERIC alcohols, `2^(@)` alcohols have lower boiling points than `1^(@)` alcohols due to a corresponding decrease in the extent of H-bonding because of steric hindrance. thus, the b.p. of butan-2-ol is lower methanolltethanolltpropan-1-olltbutan-2-olltbutan-1-olltpentan-1-ol (b) Boiling points of ethers having molecular mass equal to or less than n-butane (i.e., 58 g `mol^(-1)`) are higher than those of the corresponding n-alkanes. however, the boiling points of ethers having molecular mass equal to or higher than n-pentane (i.e., 72 g `mol^(-1)`) are lower than the corresponding n-alkanes . thus, b.p. of n-butane is lower than that of ethoxyethane. further, the b.ps of alcohols are much higher than those of alkanes, and ethers of comparable molecular masses due to intermoleclar H-bonding. however, b.ps of aldehydes are lower than those of corresponding alcohols due to absence of H-bonding but are still higher than those of alkanes and ethers of comparable molecular mass. thus, the overall INCREASING order of b.ps is n-butanltethoxyethaneltpentanalltpentan-1-ol. |
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