# Beta lactone query

While studying lactones I read that usually gamma and delta lactones are formed. Why aren't beta lactones formed. The first thought that came into my mind was angle strain. But then I thought of epoxides which have more angle strain and still are more stable. Please help.

Now similarly in the above reaction why isn't beta lactone formed?

• Two things. 1) the lactone has an additional sp2 carbons, whereas epoxides do not have sp2 carbons, so the analogy is not accurate. 2) 3-membered rings are not more thermodynamically stable than 4-membered rings - see the sections on ring strain in any (proper) org chem textbook e.g. Clayden or March. However, their formation is kinetically favoured - that means they are easy to form. – orthocresol Jan 1 '16 at 5:44
• @orthocresol could u explain y 3 mannered ring is thermodynamically stable? – Aditya Kumar Jan 1 '16 at 6:25
• I said it was not thermodynamically stable. That's mostly because of angle and torsional strain. – orthocresol Jan 1 '16 at 7:34
• @AdityaKumar. Which book is this? Please, tell me book name and its writer. – solanki... Jan 1 '16 at 7:41
• $\beta$-Lactones can be prepared by cycloaddition of ketenes with aldehydes – K_P Jan 2 '16 at 1:16

You also seem to have an incorrect assumption about the stability of epoxides. Epoxides are generally not stable with respect to nucleophilic subsitution. In fact, the Baeyer strain is so high that epoxides are commonly taught as the only aliphatic oxygen that can be displaced in an $\mathrm{S_N2}$ reaction to give the alcoholate anion and which does not need to be protonated first.