US EPA

4181455 

Journal Article 

ACIDITIES AND HOMOLYTIC BOND-DISSOCIATION ENTHALPIES (BDES) OF THE ACIDIC H-A BONDS IN ACYCLIC AND CYCLIC ALKOXYCARBONYL COMPOUNDS (ESTERS AND CARBAMATES) 

Zhang, XM; Bordwell, FG 

1994 

Yes 

Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 

59 

21 

6456-6458 

English 

10.1021/jo00100a058 

WOS:A1994PN67400058 

The equilibrium C-H bond acidities of three cyclic carboxylic esters wherein the alkoxycarbonyl group is locked into an E conformation have been shown to be about 4 PKHA units greater than those of their acyclic analogues. Also, replacement of an alpha-methylene group in 2-indanone by an oxygen atom to form a cyclic ester of this type has been shown to cause an acidity increase of a comparable magnitude. These acidity increases are roughly one-half that observed for Meldrum's acid, a similarly constituted cyclic diester, relative to that of an acyclic analogue, dimethyl malonate. A similar increase in the N-H acidity of an acyclic carbamate was found to occur when its alkoxycarbonyl moiety was locked into a five-membered (2-oxazolidone) ring. These structural changes were found to cause little or no change in the BDEs of the acidic C-H or N-H bonds in these esters or carbamates. On the other hand, introduction of a C=C bond into 2-oxazolidone caused a 15 kcal/mol decrease in BDE.