ORGANIC CHEMISTRY 15 



directions of a carbon atom in a cyclohexane ring distribute 

 themselves equally in the remaining space the angle between 

 them will be 107° 15' — that is, the groups attached, as side- 

 chains, to such a carbon atom will be closer together than in a 

 corresponding open-chain compound. In these circumstances 

 there should be a marked difference in the reactions involving 

 further ring formation between compounds of types a and h, 



Z-Z C CH3^ /C 



X— C^ X CHs-^ X 



{a) (b) 



and the spiro-compound containing the trimethylene ring 

 prepared from type {a) should be more stable than the cor- 

 responding derivative from type (b). 



Experimental evidence has shown that this is the case. 

 For example, the dibromo-ester of cyclohexane — i : i — diacetic 

 acid [I] is unstable, readily eliminating ethyl bromide to give 

 the bromo-lactone ester [II] unlike the corresponding dibromo- 

 ester of /S/3-dimethyl glutaric acid [III] 



XH Br . CO2 Et /CH (COaEt) . O 



CeHiox CeHio 



/^li Ul . V.W2 -C-L A 



io\ CeHioK 

 XH Br . CO2 Et XH Br . CO 



[I] [11] 



Me. /CHBr.COaEt 



Me^ Vh BrXOgEt 

 [III] 



Again, cyclohexane-spiro-cyclopropane-dicarboxylic acid [IV] 

 resists the action of concentrated hydrochloric acid at 240°, 

 whereas caronic acid [V] is transformed into terebic acid [VI] 

 by 5 per cent, acid at 200°. 



/CH . CO2H Me. /CH . CO2H 



C6H,o< I >C< I 



XH . CO2H Me^ XH . CO2H 



[IV] [V] 



O CMca 



I I 



COXH2XH.CO2H 



[VI] 



In the latest paper on this subject the derivatives of 

 cyclopentane are considered. In the case of a carbon atom in 



