238 Proceedings of the Royal Irish Academy. 



compounds are heated to 154° C. with acetic acid, the main products of the 

 reaction are unsaturated hydrocarbons. The alcohols prepared by us reacted 

 with acetyl chloride, forming esters. These were oily liquids which solidified 

 when placed in iced water. 



We also studied the action of acetic anhydride and sodium acetate on two 

 of the alcohols, namely, dimethyl-pentadecyl-earbinol and diethyl-heptadecyl- 

 carbinol ; and it was found that in both cases the product was a mixture of 

 esters and unsaturated hydrocarbons. While the quantity of unsaturated 

 hydrocarbon in the reaction product, as determined from the " Hubl- Waller 

 iodine number " appeared to be about the same in both cases, the quantity of 

 ester formed was much greater in the case of the dimethyl compound. Thus 

 the products of reaction of the latter substance gave an ester number repre- 

 senting about 77 per cent, of dimethyl-pentadecyl-carbinyl acetate ; while the 

 corresponding figure for the diethyl-heptadecyl alcohol was equivalent to only 

 13 per cent, of ester. The iodine numbers indicate the presence of 10 per 

 cent, of unsaturated hydrocarbon in the dimethyl derivatives, and 6 per cent, 

 in those of the diethyl compound. The total reaction was therefore greater 

 with the dimethyl compound ; while the ratio of unsaturated hydrocarbon to 

 ester formed was greater in the case of the diethyl compound. 



These facts are in complete accord with Bischoff's ' dynamic hypothesis of 

 steric hindrance. That hypothesis assumes that the open chain compounds 

 are more or less cyclic in structure and that the curvature of the chain is such 

 that the fifth or sixth carbon atom in the series approaches the first. It is 

 also postulated that the products of a reaction will be such as to give freest 

 scope for the vibrations of the carbon atoms, and hence molecules with 

 branching chains will not readily form compounds in which one atom is 

 placed in the one-five or " critical " position with respect to several others. 



Now, if we compare the formulae of the esters of the two alcohols under 

 consideration, it will be seen that the hypothesis affords an explanation of the 

 difference between the two reactions. 



I II 



C„H2, . C^Hj . C^Hj -C'- 0^ • CO • CH3' C,5 • H3, • C^Ho • C'Hj • C'- 0' • CO • CH3 



CH3, CH3-CH, 



In Formula I (dimethyl-pentadecyl-cai'binyl acetate) only one carbon atom 

 is placed in the one-five position with respect to the CO group ; whereas in 

 Formula II (diethyl-heptadecyl-carbinyl acetate) three atoms are so placed. 



1 Berichte, xxiv. (1891), p. 1087. 



