﻿202 Mr. N. McCleland on the Absorption Spectra of 



If, however, the new centre is such and so situated that 

 sr is small, yu, , 'fxm, (i. p negligible, the frequency equation 

 reduces to 



(d-^A-^yA^O, . . . (xiii.) 



where, introducing the numerical values of the constants, 



A=(l-6'25 i > 2 )(l-4-17p 2 ) 2 (l-2-59/) 2 (l-l-8^ 2 ), 

 A > = ;V60/> 2 (l-5'14 i > 2 )(l-3-14 i ; 2 )(l-3-00/9 2 )(l-4:-17 7 ) 2 )(l-2-59p 2 ). 

 Hence the /3 and 7 bands should appear and 



(A) If the new centre is on the near side of jr= ^- 



5-14 



i.e. X227, two bands will be seen in the normal 

 region [e.g. anilines 4 - n >" 22 ). 



(B) If it is on the far side of \227, only one band 

 [e.g. phenols 9 ' 10 ). 



We can also work out the cases of two centres attached to 

 one ring in the same way. The para case is the only one 

 which factorizes, and hence we expect (p. 201 note) para 

 derivatives to show narrow bands more readily than the 

 ortho and meta. This is found correct. 



VII. A u group" attached to a benzene ring, e.g. C 6 H 5 . CHO, 



benzaldehyde. 



If -33- and ^ are the inductions between the atoms of the 

 group and the carbon to which they are attached, and 

 the approximation holds, the equation is 



+ ^r 2 (Jip 2 — c'i) — 2'57yjrm l2 jr}=0 . (xiv.) 



There will be tw r o bands on the near side of A, 227 and 

 sometimes a third very near X227, e.g. benzaldehyde 21 , 

 st} r rol, methylazobenzene 25 . 



VIII. Two similar groups each united to a ring, 



C 6 H 5 N=N>-C e H 5 . 

 If 6 is the mutual coefficient of the two nearest carbons of 

 the rings, the frequency equation breaks up into 



{c 1 -(/ 1 ±m) i ; 2 }(A±^A , )=+/r(^±^) 2 A'. . (xv.) 



It follows that if the group between the phenyls gives rise 

 to a band on the near side of \250, at least two bands appear, 

 otherwise only one, e. g. azobenzene 25 , hydrazobenzene 18 , 

 and stilbene. 



