From the series, #"butane"#; #"methylbutane"#; #"neopentane"#; #"pentane"#, why does pentane have the highest boiling point?

1 Answer
anor277
Sep 4, 2016

Why? Because pentane is the most volatile of the given hydrocarbons.

Explanation:

Consider the normal boiling points of the straight chain alkanes:

#"n-butane"# #1# #""^@C#;

#"n-pentane"# #35# #""^@C#;

#"n-hexane"# #68# #""^@C#;

#"n-heptane"# #98# #""^@C#;

#"n-nonane"# #151# #""^@C#.

The longer the alkyl chain, the greater the opportunity for Van der Waals interactions between chains. Thus as the chain length increases, the boiling point increases. When crude oil is distilled, they use a fractionating tower that may be many meters high. At appropriate heights in the tower they collect off the fractions that boil between #40-60# #""^@C#, the pentanes, and the isomeric hexanes at #60-80# #""^@C# etc.

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