i6 SCIENCE PROGRESS 



a cyclopentane ring, making the same assumption as before, 

 the angle between the remaining valency directions which do 

 not take part in ring formation is 109° 46' — that is, differs by 

 but a few minutes from the normal angle. It would be expected, 

 therefore, that derivatives from cyclopentane would bear a 

 closer resemblance to those in which there was no ring present 

 than to the corresponding cyclohexane compounds, although 

 the latter more closely follow them in molecular weight. Here 

 again the experimental facts are in accordance with the pre- 

 diction. 



Ethyl aa'-dibromo-cyclopentane —1:1- diacetate [VII] like 

 the corresponding derivative of dimethyl glutaric acid, can be 

 distilled under reduced pressure practically unchanged, only 

 some 10 per cent, being converted into the bromo-lactone ester 

 [IX] though in similar circumstances the cyclo-hexane-bromo- 

 ester [I] is completely changed to the bromo-lactone ester [II]. 



CH, • CH2. /CH Br • COaEt CH, • CHg^ /CHCCOgEt) • O 



CH2 • CHa^ ^CH Br • COgEt CHa • CHa-^ Vh Br CO 



[VII] [IX] 



Similarly cyclopentane-spiro-cyclopropane -1:2 — dicarbo- 

 xylic acid [X] resembles caronic acid [V] in its action with 

 5 per cent, hydrochloric acid at 200° and differs from the corre- 

 sponding cyclohexane derivative, which is unaffected. 



CHg-CHav XH-COaH 



CHa • CHa"^ X:H • CO2H 

 [X] 



More recently, Ingold {Trans. Chem. Soc, 192 1, 119, 305) 

 has suggested an explanation of the failure of Baeyer's strain 

 theory to account for the ease of formation and for the stability 

 of some carbon rings. The heats absorbed in ring formation of 

 similarly constituted compounds by removal of two atoms 

 of hydrogen from the open-chain compounds are, according to 

 Stohmann and Kleber : 



The thermo-chemical data indicate that cyclobutane is the 

 least stable ring, and cyclohexane more stable than cyclo- 

 pentane, a state of affairs quite at variance with the predictions 

 of Baeyer's theory, but in accord with a number of experi- 

 mental observations. 



