LACTOBACILLIC ACID 23 



D and L configuration are hydrogen bonded into dimers 

 through the centers of symmetry. The trans cyclopropane 

 ring fits compactly into the regular arrangement of the 

 methylene groups along the chain. 



The unit cell dimensions of the dl-cw-9,10- and 11,12- 

 acids and of the DL-^rrt7z^-9,10- and 11,12-acids, respectively, 

 are identical within the limits of the experimental proce- 

 dures. The crystal lattices are nearly identical (isomor- 

 phous) because of the closely related arrangement of geo- 

 metrically similar structural subunits. Single crystal and 

 powder x-ray diffraction data show that dihydrosterculic and 

 DL-ci\j-9,10-methyleneoctadecanoic acid are identical (30). 



The crystal structure analysis of lactobacillic acid (33) 

 carried to the stage of locating the carbon and oxygen atoms 

 in one projection with sufficient precision to establish the 

 general stereochemistry is shown on Fig. 1.13. Taken in 

 conjunction with the chemical evidence (see Chapter 2, 

 section 4) and the crystal structure analysis of the cis-\\,\2,- 

 methyleneoctadecanoic acid racemate (32) the electron 

 density map provides conclusive evidence that lactobacillic 

 acid is D or L czVl 1,12-methyleneoctadecanoic acid. Indi- 

 vidual molecules in the racemate and the naturally occur- 

 ring species appear to have the same characteristic boom- 

 erang-like shape with the bend about the cis substituted 

 cyclopropane ring, but the packing of individual molecules 

 within the crystal lattice of the natural acid is significantly 

 different from that which occurs in the synthetic racemate. 

 The packing is less compact when all the molecules have 

 the same sense as exemplified by the lower melting point and 

 density (29° versus 37°; 0.97 g./cm.^ versus 1.005 g./cm.s) 

 of lactobacillic acid compared to DL-a5-ll,12-methyleneocta- 

 decanoic acid. In place of the centro symmetrically related 

 left- and right-handed molecules which form the hydrogen- 



