hodges - 24-9-2007 at 15:41
I know that alcohols with multiple OH- groups exist and are in fact common, but I have never run across the description of a single carbon atom
containing multiple OH- groups.
Take methane as a simple example. Methane is CH4. Substitute an OH for one of the hydrogens and you have CH3OH (methanol). But is it possible to
substitute for more of the hydrogens, giving CH2(OH)2, CH(OH)3, and C(OH)4? If not, why not?
Hodges
[Edited on 9/24/07 by hodges]
The_Davster - 24-9-2007 at 15:52
Aldehydes can exist as their 'hydrate' form which are what you describe. 'Hydrated'acetaldehyde is CH3CH(OH)2. But in the gas phase exists as the
aldehyde.
Acetals are the ether version of a dialcohol RCH(OR')2 are stable and are used as protecting groups for aldehydes and ketones in synthesis.
BromicAcid - 24-9-2007 at 16:41
You seem to be overlooking carbonic acid, two OH's on that carbon (though not exactly the example you were looking for, still, if you put some
carbonic acid under pressure in aqueous conditions you might hydrate that C=O and end up with your C(OH)<sub>4</sub>
. Remember that Ketones also have a hydrate form and these hydrate forms have various
stabilities, I'm sure some of them could even be look at as dialcohols that have an aldehyde or ketone form as opposed to the other way around.
The reason you don't get multiple OH's on the same carbon usually is just that he C=O is a more favorable configuration so the two OH groups will
consolidate given the chance. There are a number of compounds out there though where the OH's are separated by one carbon, making a kind of extended
version of what you are talking about.
[Edited on 9/24/2007 by BromicAcid]
JohnWW - 24-9-2007 at 17:16
Such compounds are called gem-diols. They are very liable to lose a molecule of H2O to become ketones or aldehydes, which in aqueous solution exist in
equilibrium with the gem-diols.
Compounds in which the OHs are on adjacent carbons are called vic-diols. This also occurs in some saccharides. If both Cs also have an H atom on them,
they decompose on heating to an alkene plus H2O.
not_important - 24-9-2007 at 18:03
The gem-diol structure can be stablised by electron withdrawing groups on adjacted carbons - chloral CCl3CHO reacts with water to for the stable
chloral hydrate CCl3CH(OH)2 .
Formaldehyde in aqueous solution is mostly in the gem-diol form, but reverts to the aldehyde as water is evaporated or otherwise removed.
Sauron - 24-9-2007 at 19:20
There are also hemiacetals which are a hydroxyl and an OR on same C.
And thioacetals, thioketals, etc that are the S equivalents.
Often used as PGs or masking agents for prep of aldehydes and ketones, as in the fine work of my old prof Al Meyer, See Meyer aldehyde synthesis under
Name Reactions in Merck.
guy - 25-9-2007 at 01:22
Too many oxygens make it hard to form bonds with other things. It will just break off. For example, R-C(OH)3 will just break off into R-H and H2CO3
which easily breaks up into H2O and CO2. In fact, an [R-CO2(OH)]<sup>2-</sup> intermediate may be responsible for decarboxylation
reactions involving NaOH.
sparkgap - 25-9-2007 at 04:22
Hodges.
CH(OH)3, and C(OH)4, as written, don't actually exist; but they do have proper IUPAC names: orthoformic acid and orthocarbonic acid, respectively.
You can have, however, esters of these that are called, not surprisingly enough, orthoformates and orthocarbonates. You can Google on those for more
information.
sparky (~_~)