[Hubert]

Can octanol be considered as a polar solvent? If yes, Do they deactivate the Nucleophile?

[Donaldson Tan]

octanol is a polar solvent, in virtue of its -OH group. Being a protic solvent, the H of -OH bonds to the (negatively charged) nucleophile. This makes the nucleophile very bulky and thus kinetically hinder nucleophilic behavior. This deactives the nucleophile, and in some cases, favours other possible pathway consequently (eg. elimination vs substitution in halogenoalkanes)

[Hubert]

since u say Octanol is a polar solvent, then why does it not dissolve in polar solvent fer eg water...if it is not a polar solvent, then how does octanol deactivate the nucleophile? pls reply asap...coz i realli want to understand this part...thanks!

[lemonoman]

For chain alcohols, I was always taught that the molecule could be considered polar (dissolvable in water) if it had 5 or less carbons per hydroxyl (OH) group.  So octanol which has 8 carbons would NOT dissolve in water...

It seems like an arbitrary rule, but there are reasons to do with dipoles, etc.

Hope this helps.

[Hubert]

so...erm does it deactivate the nucleophile and help to stablize the carbocation? btw do can i help your email? send your email to my email...Exterminator_hubert@hotmail.com

[Donaldson Tan]

Like dissolve like is a general rule of the thumb. The fact is the carbon chain in Octanol is so big that the -OH is insiginificant in terms solute-solvent interaction with water. Overall, octanol is insoluble in water.

However, the -OH group of octanol allows it to be bonded to the nucleophile. It makes the nucleophile very bulky, thus providing kinetic hindrance to nucleophillic reaction. The nucleophile is consequently less mobile, thus its nucleophillic strength is reduced.

[Hubert]

i thought the polar bonds will bond to the carboncation instead of the nucleophile?

[movies]

Polar things will bind to both positively and negatively charged ions.  However, their binding effectiveness is not always the same for the two.

Saying that a particular molecule is "polar" or "non-polar" is a very subjective description.  Solvent polarity is more of a coninuum than two distinct groups.  The test of a whether or not a molcule is "polar" should not be whether or not it is soluble in water.  As we have agreed in this thread, octanol is not miscible with water but I don't think anyone here would argue that octanol is "non-polar" when compared to something like hexane.

Einstein had it right: it's all relative.

[Hubert]

so u are meant that octanol is still a polar solvent when relative to water? however it is not soluble in it because of the insignificance of the -OH?

[movies]

Octanol is less polar than water.  The insolubility is due to the large alkyl (non-polar) domain.  There is still a hydroxyl group, which is certainly a polar functional group.

[arnyk]

The only thing that is completely covalent would be diatomics according the electronegativities, the rest can be classified to different "degrees" of polarity.  Like sugar won't conduct electricity but that doesn't make it covalent,  we could probably say low polar.

[movies]

Technically atoms would also be non-polar.

[arnyk]

Individual atoms?  

[movies]

Sure.  It doesn't get much less polar than helium!

Although I suppose you could argue that helium isn't organic and shouldn't be considered in this context....

[Hubert]

huh?