melting point question

[jayballer125]

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Which has the highest melting point

a) 3 carbon chain and 3 carbons branching
b) 2 carbon chain and 4 carbons branching

I was thinking its B bc the more branching there is, the higher the melting point. but bc A has a longer chain, can that make that one the higher mp???

 

[DentalDeac]

I thought high branching meant a lower MP.

 

[Mstoothlady2012]

It all depends on the molecules actually.

But generally branching increases the melting point. Basically melting point increases when the molecule can pack tightly and branched molecules can do this job better. But there are molecules that don't follow this rule.

 

[DentalDeac]

It all depends on the molecules actually.

But generally branching increases the melting point. Basically melting point increases when the molecule can pack tightly and branched molecules can do this job better. But there are molecules that don't follow this rule.

This doesn't make sense to me, linear molecules should be able to pack more tightly than branched molecules.

 

[Mstoothlady2012]

This doesn't make sense to me, linear molecules should be able to pack more tightly than branched molecules.

Refer to this thread...

http://forums.studentdoctor.net/showthread.php?t=543003

 

[jayballer125]

so would it be A or B????

 

[Mstoothlady2012]

so would it be A or B????

dude your molecules don't make sense to me. Give me real molecules to work with and i will try my best.

How can you have 2 carbons with 4 branching carbons? Sorry but i am not able to draw it out....

 

[flycd05]

i think it would be B b/c MP really emphasizes symmetry. so the more symmetry a molecule has, the higher its melting point.

 

[jayballer125]

2 carbon with 4 carbons branching would be like 1,1 dimethyl 2,2 dimethyl ethane 2(CH3)CH - CH(CH3)2. i think...........

 

[Mstoothlady2012]

2 carbon with 4 carbons branching would be like 1,1 dimethyl 2,2 dimethyl ethane 2(CH3)CH - CH(CH3)2. i think...........

that's same as 2,3 -dimethyl butane

 

[Mstoothlady2012]

Anyways let me just compare between these 2

A) looks like 3-methyl pentane
B) looks like 2,3,-dimethyl butane

Between these B would have higher melting point, b/c it has more branching and it is more symmetrical.