German
Harmless
Posts: 44
Registered: 13-5-2009
Member Is Offline
Mood: No Mood
|
|
Do I retain stereochemistry, alcohol>tosylate>halide?
I know I retain stereo-chemistry going from alcohol to tosylate. And I know I retain stereo-chemistry going from PRIMARY alcohol to alkyl halide. But
do I retain stereo chemistry going from a primary alcohol to the tosylate then to the alkyl halide? Since the tosylate attaches at the oxygen I feel
that when the iodine replaces the oxygen that an inversion occurs???? Or no? Could someone please help me here. Thank you (I'm aware this is a dumb
question I should know).
[Edited on 5-8-2023 by German]
|
|
|
SyntheticFunk
Harmless
Posts: 21
Registered: 30-12-2022
Member Is Offline
|
|
It’s an inversion.
When substituting a functional group, it will either racemize due to a carbocation intermediate, or invert due to following an SN2 mechanism.
Primary carbocations (as one would expect for an SN1 mechanism) are quite unstable. Therefore, it is more likely that the reaction will proceed via an
SN2 mechanism and invert the stereochemistry.
The reason tosylate retains the stereochemistry Of the alcohol is because the alcohol isn’t being substituted by OTs. Rather, it is acting as a
nucleophile and attacking TsCl
|
|
|
Texium
Administrator
Posts: 4521
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
SF is correct, but more importantly, there’s no stereochemistry to speak of if you’re working with a primary alcohol! Unless you have an
asymmetric secondary alcohol, you don’t have a stereocenter.
|
|
|
SyntheticFunk
Harmless
Posts: 21
Registered: 30-12-2022
Member Is Offline
|
|
Good point Texium, I had overlooked the fact that **the carbon of** primary alcohols can’t be chiral.
Edit: technically this is not 100% true either, as one could possible have a compound like fluorochlorobromomethanol, which would be chiral, though
unlikely to exist.
[Edited on 7-8-2023 by SyntheticFunk]
|
|
|
DraconicAcid
International Hazard
Posts: 4280
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
Well, they can be, but the stereocentre will be in another part of the molecule, and won't be affected by the reaction of the alcohol.
For example, (R)-2-methyl-1-butanol will give (R)-1-bromo-2-methylbutane.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
