~ : ; 



670 Mr. N. P. McCleland on the 



3. If in the case of two electrons u = v, L==N, we find 



•Hi 



L + M 



If p is the frequency of the least refrangible absorption 



band of the molecule p 2 = ^ ^, where c is the rigidity 



coefficient, and consequently $ = 2a 2 \ ~¥a \ ' 



From this it may be deduced that in the symmetrical, and 

 probably in not too asymmetrical cases, if in substances of the 

 same kind we find one where the less refrangible band has an 

 unexpectedly small frequency, the "vibration group" will be 

 more reactive than is usual in that substance. 



For example, the absorption bands of the aliphatic 

 aldehydes are markedly on the less-refrangible side of those 

 of the ketones (and this is most marked in the case of 

 formaldehyde), although the absorption is in each case due 

 to the carbonyl group, and the methyl group usually shifts 

 the band in the opposite direction : the ease with which the 

 carbonyl group of aldehydes, particularly formaldehyde, 

 reacts (in particular, polymerizes) is well known. 



4. Thiele's theory is easily deduced from the above con- 

 siderations. 



In a substance of the type 



C=CH— OH=(T 



E/l 2 3 4 X E, 4 



it is easy to see that from the considerations given above the 

 stabilizing influence on the unsaturated carbons 2, 3 is 

 greater than on 1 and 4, provided none of the R 3 groups are 

 themselves unsaturated. Therefore addition will take place 

 more readily on to carbons 1 and 4 than on to 2 or 3, which 

 i.s Thiele's theory. 



It may be remarked that substances like 



C 6 H r .\ /CbH 



> = CH-CH=< 



L 5 



are exceptions to the theory, which is just what one would 

 expect from the proviso stated above. 



Also the above does not apply to a substance like 



D X C = CH— CH 2 —CH = c' ' 

 *Vl 2 3 4 5 R i 



