alcohol boiling point question

[glk2101]

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why does 1-hexanol have a higher boiling point than 1-butanol?
i thought that with increased alkyl groups, the h-bonding isnt as strong..so wouldn't that mean 1-butanol would have the higher bp?

 

[ZenoVT]

The general trend with these type of questions is that if you have the same functional groups the molecule with the higher molecular weight will have the higher boiling point.

 

[glk2101]

but isnt it true that butanol is more soluble in water than hexanol because of greater degree of H bonding?
wouldnt that mean it should have a higher boiling point as well?

 

[ZenoVT]

but isnt it true that butanol is more soluble in water than hexanol because of greater degree of H bonding?
wouldnt that mean it should have a higher boiling point as well?

Well yes and no. Don't make solubility in water your reasoning why molecules have higher or lower boiling points and you'll be straight.

 

[tranv117]

but isnt it true that butanol is more soluble in water than hexanol because of greater degree of H bonding?
wouldnt that mean it should have a higher boiling point as well?

dont confuse solubility with boiling points. 1-hexanol has greater molecular weight, more dispersion forces so greater boiling point.

 

[glk2101]

ok i get it thanks guys!

 

[pasionatdentist]

How does branching affect B.P?
How about if we are comparing primary, secondary or tertiary alcohols with the same weight? Please help..............

 

[glk2101]

How does branching affect B.P?
How about if we are comparing primary, secondary or tertiary alcohols with the same weight? Please help..............

so if you are looking at constitutional isomers of C4H10, then as branching increases you are essentially lowering the surface area..by doing this you are in turn lowering the van der waals forces b/w molecules..so with weaker forces b/w molecules you will have a lower boiling point

now if you are talking about melting point, this trend sometimes can be opposite..increased branching can actually raise melting point if the branched molecule can fit more easily into lattice form

 

[Doa110]

How does branching affect B.P?
How about if we are comparing primary, secondary or tertiary alcohols with the same weight? Please help..............

Branching decreases Boiling and Melting point.
However B/W Cis and Trans, Trans has higher melting points and Cis has higher Boiling point.

 

[gentile1225]

doa are you sure about that? im a little confused.

 

[doc3232]

Branching decreases Boiling and Melting point.
However B/W Cis and Trans, Trans has higher melting points and Cis has higher Boiling point.

cis has a higher boiling point because it is more polar. Hence more interactions.