AMMRL: diastereotopic?

Jeff Simpson (jsimpson@mit.edu)
Fri, 8 Feb 2008 16:30:58 -0500 

This is a multi-part message in MIME format.

------=_NextPart_000_00A7_01C86A6F.FCEF1460
Content-Type: text/plain;
	charset="US-ASCII"
Content-Transfer-Encoding: 7bit

Hey all,

 

I am teaching a class in NMR and I was pondering the differences between
homotopic, enantiotopic, and diastereotopic atoms and groups.

 

If I have t-butyllcyclohexane (with the t-butyl group equatorial at the 1
position of the ring), are the H's on C4 diastereotopic?  The definition I
am getting for diastereotopicity is that there has to be a chiral center in
the molecule somewhere else for diastereotopicity to occur.

 

It is clear that the axial and equatorial H's on C4 should have different
chemical shifts, but are they diastereotopic?  Is there another, perhaps
better, term to describe this proton pair?  Do I just say they are
"chemically distinct" because of the ring's chair conformation but NOT
diastereotopic?  Clearly the two cannot be separated into pro-R and pro-S.

 

Send me your vote/explanation, and I'll post a summary if there is
sufficient interest.

 

Jeff

 

Jeff Simpson, Director

Department of Chemistry Instrumentation Facility 

Massachusetts Institute of Technology

77 Massachusetts Avenue, 18-0090

Cambridge, MA, 02139

617-253-2016 (1806 lab)

 


------=_NextPart_000_00A7_01C86A6F.FCEF1460
Content-Type: text/html;
	charset="US-ASCII"
Content-Transfer-Encoding: quoted-printable























Hey all,



 



I am teaching a class in NMR and I was pondering the =
differences
between homotopic, enantiotopic, and diastereotopic atoms and =
groups.



 



If I have t-butyllcyclohexane (with the t-butyl group
equatorial at the 1 position of the ring), are the H’s on C4
diastereotopic?  The definition I am getting for diastereotopicity =
is that
there has to be a chiral center in the molecule somewhere else for =
diastereotopicity
to occur.



 



It is clear that the axial and equatorial H’s =
on C4
should have different chemical shifts, but are they =
diastereotopic?  Is
there another, perhaps better, term to describe this proton pair?  =
Do I
just say they are “chemically distinct” because of the =
ring’s
chair conformation but NOT diastereotopic?  Clearly the two cannot =
be
separated into pro-R and pro-S.



 



Send me your vote/explanation, and I’ll post a =
summary
if there is sufficient interest.



 



Jeff



 



Jeff Simpson, Director



Department of Chemistry Instrumentation Facility =




Massachusetts Institute of =
Technology



77 =
Massachusetts
  Avenue, =
18-0090



Cambridge, MA, 02139


617-253-2016 (1806 lab)



 









------=_NextPart_000_00A7_01C86A6F.FCEF1460--