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13) The correct order of melting points of isomeric pentanes is (A) n-Pentane > iso-Pentane > neo - Pentane (B) neo-Pentane > n-Pentane > iso-Pentane (C) neo-Pentane > iso-Pentane > n-Pentane (D) n-Pentane > neo-Pentane > iso-Pentane Explain the ansss plzzz.....









13)




The correct order of melting points of isomeric pentanes is





(A)  

n-Pentane > iso-Pentane > neo - Pentane





(B)  

neo-Pentane > n-Pentane > iso-Pentane





(C)  

neo-Pentane > iso-Pentane > n-Pentane





(D)  

n-Pentane > neo-Pentane > iso-Pentane





 


Explain the ansss plzzz.....

Grade:12

4 Answers

sushant singh
66 Points
11 years ago

hey geoff,

the answer to your question is option B

(B)  

neo-Pentane > n-Pentane > iso-Pentane

with incresing order of melting points...

as :

isomers          Melting point(Co)  

n-pentane                −129.8

isopentane               −159.9

neopentane              −16.6

Geoffrey Richards
34 Points
11 years ago

Hey thank you for the ans but can u say how to predict it ....???

Ashwin Sinha
520 Points
11 years ago

Correct answer is (A)., bcoz, chain with no branch has more vanderwaal attractions. This declines with inc. in branching!!!!!!!

 

           Good Luck!!!!!!!

   Plz. approve!!!!  Plz!!!!!!!!

sushant singh
66 Points
11 years ago

yeah geoff, 

 if you consider the Rotation about two central single C-C bonds of n-pentane produces four different conformations.

Even, the melting point of neopentane, the most heavily branched of the three, is 100 °C higher that of isopentane. The anomalously high melting point of neopentane has been attributed to the better solid-state packing assumed to be possible with its tetrahedral molecule; but this explanation has been challenged on account of it having a lower density than the other two isomers. The branched isomers are more stable (have lower heat of formation and heat of combustion) than normal pentane.

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