Esters (1 Viewer)

[randhi]

Okay, i'm really confused

are esters polar or non-polar
because one person says that its polar and the other says that it isn't??
is it cos the C=O bond is surrounded by the non-polar hydrocarbon bonds that neutralises its effect making it non-polar. is that right

 

[mervvyn]

Okay, i'm really confused

are esters polar or non-polar
because one person says that its polar and the other says that it isn't??
is it cos the C=O bond is surrounded by the non-polar hydrocarbon bonds that neutralises its effect making it non-polar. is that right

Esters are polar because of the C=O and C-O bonds, but they are only dipole-dipole and thus not as strong as hydrogen bonds. p170 of conquering chem if you need more.

 

[tennille]

They differ to alkanoic acids and alkanols which can form hydrogen bonding with water, etc. Esters form dipole dipole bonds which are weaker. This results in a lower boiling pt. to the corresponding alkanols and alkanoic acids which form the ester. So yeah, they are polar. Alkanes and alkenes are non- polar.

 

[tennille]

I know ethanol is like that- both non- polar and polar. The alkyl chain is non- polar whilst hte hydroxy end is polar making it a suitable solvent.

 

[randhi]

okay thanks guys, i guess four against one are good odds.

 

[xiao1985]

ester does not have a dipole...

yes, there is a tendency for electrons to be drawn to the middle of the molecule, but that only leaves ester postively charged on both ends... so the ester molecule will really look liek this:

+ - +

since the ends do not have opposite charges, there will be minimal dipole interactions...

 

[tennille]

The point is that it is polar. I don't think we need to know it in too much depth.

 

[Xayma]

Not in any significant capacity.

Really its only as polar (well not really but you get the idea) as C-C=C-C is.

 

[sHin]

While on the topic of esters..

I remember seeing a trial question like this:
A solution mixture of ester, alkanol, alkanoic acid and water is in a container. What are the layers?

How does an ester's density compare to alkanols and alkanoic acids?

 

[Tommy_Lamp]

you would see which are soluble in each other and which arent etc.

then determine the layers

 

[mervvyn]

While on the topic of esters..

I remember seeing a trial question like this:
A solution mixture of ester, alkanol, alkanoic acid and water is in a container. What are the layers?

How does an ester's density compare to alkanols and alkanoic acids?

my guess is that the alkanol would be soluble in water, esp. if it was a small hydrocarbon one, and the acid might go either way, depending on how big the carbon chain was, and then the ester will be by itself or with the acid. that's only a guess though.

 

[xiao1985]

acid will go either way dependin on size of alkonaic acid/acidity of the soln...
alkanol again depend on size of molecule and if a strong base is present.
ester probably won't

 

[mr EaZy]

esters will be in the insoluble layer, wont they? i read somewhere theat they are insoluble in water.

there will be a clear (h20) layer and a yellow organic layer where the ester will be (in the liebig condenser)

 

[randhi]

Yeh, they are. the ester is on the layer above the water. okay so a ester is polar but then doesn't that mean it would soluble in water. or would u for this instance say that it is non-polar to justify why it is doesn't dissolve in water

 

[tennille]

In Conquering chemistry, it says it's polar- im just going by that. Or maybe the textbook stuffed up on that as well as hte eutrophication stuff...

 

[tina_goes_doo]

The point is that it is polar. I don't think we need to know it in too much depth.

Although all you need to know is wether an ester is polar or not, it is still a good idea to know why etc. in case they ask you a similar question. It never hurts to have a sound learning of things esp in chem.

 

[McBean88]

hmm...i was thinking...maybe the polarity of an ester depends on the location of the C=O bond in the molecule. so if it appears in the middle of the ester it would be polar, as demonstrated by xiao1985. but if it wasn't than it would be polar. the occurrence of this type of ester is much more common so thats probably why textbooks generally say its polar...
and maybe it isn't very soluable in water because of the C=O bond. even though the ester is polar, the water molecules may not be "strong" enough to break this bond...

don't take my word for it though...just thoughts...=/