1
$\begingroup$

Is this Newman projection energy profile for 2,3-dihydroxypropanal correct?

Also, I was to identify R/S configuration for the initial Newman projection. I am pretty sure it is R, but I need help here as well.

|improve this question
$\endgroup$
  • $\begingroup$ This is too tough to answer as is. There may be hydrogen bonding, so the energy profile could be highly dependent on solvent. (R)- is correct though. $\endgroup$ – Zhe Jan 16 '17 at 14:47
  • $\begingroup$ I think fifth structure (in which OH is gauch to both CHO and OH) is most stable and has minimum energy . It is due to H bonding of OH with both O of CHO and H of OH. $\endgroup$ – narendra kumar Jan 16 '17 at 14:55
1
$\begingroup$

There seems to be only one problem. The 240° conformer* will be lower in energy as compared to the 120° conformer as there will be hydrogen bonding between the two hydroxyl groups . Rest all looks good.

|improve this answer
$\endgroup$
  • $\begingroup$ *a conformer is also called a rotamer or rotational isomer. Anyways R is correct $\endgroup$ – Raghav Jan 16 '17 at 14:52
  • $\begingroup$ Perfect, my professor had not mentioned anything apart from steric conditions, so I had not even considered it! Would you mind telling me what steps I should go through to assign the relative energies when plotting the diagram? I really struggle with more complicated examples and I am afraid I will not have time on the final exam. All comments appreciated! $\endgroup$ – Bee Jan 16 '17 at 16:14
  • $\begingroup$ Actually I think your professor is quite right. Steric and torsional strains are the fundamental factors that affect energy. Things such as H bonds arise only as exceptions. The standard approach would be to do what you have done above in your drawing and then look for any additional factors that could change your graph $\endgroup$ – Raghav Jan 16 '17 at 16:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.