Talk:Mod:smistry77
Comments
Cyclopentadiene (0.20)
Just mention that the hydrogenation reaction is thermodyncamically controlled. You imply it, but you don't state it.
Taxol (0.25)
what is an atropisomer?
NMR:
You are completely right about the rotation at room temperature. Nice way of representing it, but putting the averaged values into the table might be easier to read at one glance.
Also, please order the table by shift, not by atom number. The atom numbers are arbitrary, ordering by shift will be more to how one perceives an experimental spectra.
"An explanation for this is the position of the proton inside the ring rather than statically outside the ring." Or, in more general terms, the shift of the methylidyne group is highly sensitive to changes in conformation/orientation.
Carbon 1:
Buzzword bingo?!
You'd have to explain what the anomeric effect is and how it physically takes place:
donation of electron density from which to which orbital?
Where is your donating moiety?
Do you have any experimental values to support your bond lengths.
One more physical explanation for origin of the bond length, is the heavy atom effect. The calculational method used (i.e. the basis set) is not precise enough to describe the heavier sulfur atoms and their orbital interactions.
You need to be more precise.!
Epoxide (0.05)
Again, please be more detailed. Maybe explain the anomeric effect in a bit more detail, show which bonds (atom numberS?) you're talking about and/or add them to your graphic. Which one is the "methylene" - all the carbon atoms are sp3-hybridized?
Why do you put two structures? Are they the same, are they different?
NMR (0.05)
You should not expect any difference in NMR for different enantiomers. Go back to your lecture notes on enantiomerism - I'm sure they cover that.
The NMR of (S)-styrene should be absolutely identical to the (R) conformer.
If you draw two structures and optimise them, you'll always end up with slightly different relaxed geometries. In order to get the exact opposite structure, you can use Gaussviews "mirror invert" option.
Optical Rotation and TS (0.35)
Yes, it looks nice, but:
There's many more data points for the methyl styrene (scan reaxys for optical rotation) between -39° and -144°, you need to discuss this. And while the data looks nice you'll need to consider the reliability of the method for alpha values below 100° and discuss it accordingly. (It's stated in the wiki.)
Also, reaxys shows different values between for the Trans-β-methyl Styrene Oxide between 0 and 50°).
You cannot just state (or imply) that all those experimental values that don't fit your calculation are wrong. You're doing this by giving those values in your table which implies that everything worked right. Seemingly only as a side note you mention in the text that the values in table are not actually very reliable.
There's a number of reasons: It could be that your calculation was not completely right (geom. structure slightly off, no solvent molecules considered). There could also be any number of reasons for the experimental data to be off (temperature, impurities, enantiomeric mixtures, someone doing a mistake etc.)
You have to phrase your discussion carefully.
In the end, all you can say is that "probably" these data points are correct, but you cannot be 100% sure. Your conclusion could also explain how to best find out (e.g. by using a combined experimental/calculational approach where you take care not to do any of the possible errors I mentioned above).
enantionmeric excess:
How does that compare to literature? You need to verify your findings!
QTAIM and NCI (0.10)
"This large interaction may be controlling the stereochemistry "
Well, better to first state the things that you can say with certainty: The large interactions stabilizes the intermediate complex. THen you can go ahead and state your assumptions.
Also be careful, bond critical points do not directly correlate to either a bond or an NCI. They can, but they don't have to. try to be more precise please!