User talk:Mcpazzo
Conformational problems
Please stop conflating the idea of a "single bond" meaning a bond at one place with a "single bond" meaning a σ bond. The Gold Book is quite clear (and chemistry agrees:) that rotations are in relation to a σ bond, not just a bond. Your latest change confuses all of the ideas: "rotations about single or multiple bonds" suggests that a multiple bond (alkene) can rotate. Likewise, "Rotamers are conformers that differ by rotation about one only a single bond" would include alkene cis/trans isomerism, since the only one bond (a "single bond") is rotating (the "single" here is redundant with σ, the "one" is not redundant with "single"). DMacks (talk) 18:56, 29 September 2008 (UTC)
- n-Butane has gauche+ and gauche– too. Looking down the C2–C3 bond from either direction gives the same sign: the symmetry is an improper rotation not a plane. DMacks (talk) 19:01, 29 September 2008 (UTC)
You're right. I made some further changes to clarify it in Conformational isomerism. One problem was that I was trying to clarify that a rotamer is rotation about one sigma bond, a conformation can involve many. A rotamer is a conformer. I did not mean to multiple bonds sound as though it was a higher bond order. There is rotational barrier about a double bond but I don't think people usually call this a rotamer or conformer. It looked as though we were maybe editing the page at the same time on the 29th, which you may have perceived as me changing things back to my wording when yours was more exact. User:Mcpazzo (talk) 10:51 08-Oct-2008 PDT
I'm sorry but this sentence "The molecular geometry can be determined by various spectroscopic methods (IR or FRET for distances, Microwave for rotations , NMR for angles and distances) and X-ray crystallography for solids" after your recent edit, contains several errors. Microwave spectroscopy in the gas phase gives distances and angles from the rotational lines. IR gives the same from the rotational fine structure. NMR, as usually done, does not give distances and angles. However solid NMR can do so. FRET does not give structure as far as I know. You miss electron and neutron diffraction and Raman spectroscopy which are all commonly used. I have attempted to rewrite the whole section. --Bduke (Discussion) 06:32, 9 October 2008 (UTC)
- Thanks. NMR can give dihedral angles through coupling constants and I was referring to NOE-type experiments to determine relative distance (maybe not very accurately). These things were not discussed before my change, so I am glad you are adding to it. FRET can definitely determine distances. I will find a reference for that when I have the chance. Mcpazzo (talk)Mcpazzo 9:47, 08-Oct-2008
- OK. I think there is a lack of clarity between "molecular structure" meaning the linkages and bonds in the molecule and "molecular structure" meaning the determination of the coordinates of all atoms in the molecule, i.e. bond lengths, bond angles and torsion angles. Spectroscopy can give the former in solids and liquids, but the latter comes from the rotational fine structure only really observed in the gas phase. On a different point, your last edits have made several references as self-references. We do not make references to other wikipedia articles. That is against policy. The wikipedia links should be worked into the article text and not into the references. --Bduke (Discussion) 21:22, 9 October 2008 (UTC)
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