I didn't recognise the spiroketal as such, but knew it was a ketal. It was rather hard to expect a second year student to work out the enantiomeric form without some molecular models. I've even forgotten about the anomeric effect. But in all fairness, todays students have the internet to help them. In my day, there was no internet. Only difficult textbooks and even more difficult research papers. I can remember the Newman projection though. It's always a problem though. What you don't use you forget. But learning is a lifelong activity. Always try and learn something new. My question to the Prof was how were the conformations studied (H-nmr at low temps?). It would be nice to see some evidence. It was a trip down memory lane. The students must by now have graduated a long time ago. I wish them well.
