Indanone and Other Keto Derivatives of Indane

Returning now to the discussion of other carbocyclic species, we will consider the process involving 1-indanone and other keto derivatives of indane. We expect no special stabilization or destabilization over that of indane - none of these species may be expected to be aromatic or antiaromatic save that of the benzene ring therein. Starting with 1-indanone itself (X = CO, Y = Z = CH2)  

Using the enthalpy of formation of 1-indanone from [29], we find this reaction is exothermic by 8.1 kJ mol 1. We are not surprised that this reaction is less exothermic than the earlier one (1) because we have lost the conjugation energy associated with conjugation of a carbonyl group attached to a benzene ring. 

Consider now the related reaction with the isomeric 2-indanone [29] (X = Z = CH2, Y = CO)  

This reaction is exothermic by only 14.6 kJ mol 1, in line with our expectations, since 2-indanone lacks the conjugation found in its 1-isomer. The exothermicity for 2-indanone is not the same as it is for indane. Then again, do we really expect the strain energy for 2-indanone to be the same as for indane Are our concepts really precise to that degree of thermochemical resolution  

Finally, consider indane-1,3-dione [29] (X = Z = CO, Y = CH2) (XVII), where we make use of the value for 2,4-pentanedione, the tautomer specified [30], and not the enol-majority mixture that is usually named this species (or even more commonly, but strictly speaking misnamed, acetylacetone )  

---