happyana

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ok, so double bonding causing a compound to have a lower boiling and melting point right? kaplan and destroyer are telling me two different things. it says that for unsaturated fatty acids, the BP is lower since the kinks in the compound make it fluid-like which makes it easier to boil than saturated compounds. But Kaplan says that double bonding causes a little bit more polarity so it causes compounds to have a higher BP.
 

doc3232

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ok, so double bonding causing a compound to have a lower boiling and melting point right? kaplan and destroyer are telling me two different things. it says that for unsaturated fatty acids, the BP is lower since the kinks in the compound make it fluid-like which makes it easier to boil than saturated compounds. But Kaplan says that double bonding causes a little bit more polarity so it causes compounds to have a higher BP.
They are both true. Polarity from a double bond causes a higher BP, but the double bond in the fats causes weaker stacking and hence a lower BP.

You need to understand each point of view, to sum it up:
Stacking of molecules (non-branching) causes a higher BP due to interactions
Polarity causes a higher BP due to interactions
Higher Molecular weights causes lower BP
 

happyana

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ok, so for example, between n-butane and n-butene, butene would have a higher BP then? or i mean wouldn't this prevent stacking too? ah! does that only occur in fatty acids?
 
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doc3232

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ok, so for example, between n-butane and n-butene, butene would have a higher BP then? or i mean wouldn't this prevent stacking too? ah! does that only occur in fatty acids?
Well, the double bond would allow for some dipole interactions which would higher the BP.

Fatty acid chains are about 12 carbons long so the angle difference created by the 1 double bond has a big effect on the stacking.
From a plasma membrane you would notice this a lot more because it affects the permeability.

I think the questions on the actual DAT will be very clear, just know the basics and reason you way through it on the test.
 

sciencegod

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there's no such thing as a dumb questiinhere. some know a little more than others but were all students studying for dat. no one should feel ashamed to ask what they don't know. were all here to help each ither and were glad to answer anything that u don't understand. together we can murder this dat. (this almost brings tears to my eyes :) )
 

Danny289

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as doc said in previous post both statements are true, in fats usually you are dealing with the chain over 16-18 carbons but what kaplan says, you have small numbers like 2-4 carbons.
hahahaa there is a German saying:" there is not stupid question, but the answer can be stupid." :laugh:
 
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